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WO2017108311A1 - Système et procédé lithographiques - Google Patents

Système et procédé lithographiques Download PDF

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Publication number
WO2017108311A1
WO2017108311A1 PCT/EP2016/078482 EP2016078482W WO2017108311A1 WO 2017108311 A1 WO2017108311 A1 WO 2017108311A1 EP 2016078482 W EP2016078482 W EP 2016078482W WO 2017108311 A1 WO2017108311 A1 WO 2017108311A1
Authority
WO
WIPO (PCT)
Prior art keywords
sub
radiation
beams
configuration
assembly
Prior art date
Application number
PCT/EP2016/078482
Other languages
English (en)
Inventor
Vadim Yevgenyevich Banine
Wilfred Edward ENDENDIJK
Han-Kwang Nienhuys
Rilpho Ludovicus DONKER
Erik Roelof Loopstra
Original Assignee
Asml Netherlands B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Asml Netherlands B.V. filed Critical Asml Netherlands B.V.
Publication of WO2017108311A1 publication Critical patent/WO2017108311A1/fr

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/70991—Connection with other apparatus, e.g. multiple exposure stations, particular arrangement of exposure apparatus and pre-exposure and/or post-exposure apparatus; Shared apparatus, e.g. having shared radiation source, shared mask or workpiece stage, shared base-plate; Utilities, e.g. cable, pipe or wireless arrangements for data, power, fluids or vacuum
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70008—Production of exposure light, i.e. light sources
    • G03F7/7005—Production of exposure light, i.e. light sources by multiple sources, e.g. light-emitting diodes [LED] or light source arrays
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70058—Mask illumination systems
    • G03F7/70208—Multiple illumination paths, e.g. radiation distribution devices, microlens illumination systems, multiplexers or demultiplexers for single or multiple projection systems
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/0903—Free-electron laser

Definitions

  • the present invention relates to a lithographic system.
  • the present invention may relate to a lithographic system comprising two or more free electron laser radiation sources.
  • a lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate.
  • a lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
  • a lithographic apparatus may for example project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.
  • a patterning device e.g. a mask
  • a layer of radiation-sensitive material resist
  • the wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features which can be formed on that substrate.
  • a lithographic apparatus which uses extreme ultraviolet (EUV) radiation being electromagnetic radiation having a wavelength within the range 4-20 nm, may be used to form smaller features on a substrate than a conventional lithographic apparatus (which may for example use electromagnetic radiation with a wavelength of 193 nm).
  • EUV extreme ultraviolet
  • a lithographic system may comprise one or more radiation sources, a beam delivery system and one or more lithographic apparatuses.
  • the one or more radiation sources may comprise a free electron laser.
  • the beam delivery system may be arranged to deliver radiation from one or more of the radiation sources to each of the lithographic apparatuses.
  • a Free Electron Laser or FEL may be a good candidate for an EUV lithography source.
  • current projectable FEL uptime may be of the order of 94% to 98%.
  • the downtime of an FEL may cause a complete fab down, i.e. a complete cessation of a fabrication facility.
  • a system comprising a first radiation source configured to provide a first radiation beam; at least one splitter configured to split the first radiation beam into a first plurality of sub-beams; a second radiation source configured to provide a second radiation beam; at least one further splitter configured to split the second radiation beam into a second plurality of sub-beams; and a switch assembly moveable between first and second configurations, wherein the switch assembly is configured to: receive at least one of a first sub-beam which is one of the first plurality of sub-beams and a second sub-beam which is one of the second plurality of sub- beams; in a first configuration, transmit the first sub-beam along a desired path; in a second configuration, transmit the second sub-beam along said desired path.
  • the first radiation source and/or the second radiation source may comprise a free electron laser.
  • the switch assembly may be further configured to in the first configuration dump the second sub-beam, and/or in the second configuration dump the first sub-beam.
  • the transmitting of the first sub-beam or the second sub-beam along the desired path may comprise transmitting the first sub-beam or second sub-beam to a lithographic apparatus.
  • a first sub-beam from the first radiation beam or a second sub-beam from the second radiation beam may be supplied to the lithographic apparatus.
  • a switch assembly or switch assemblies after the beams are split by beam splitters a separate switch assembly may be provided for the sub-beam supplied to each lithographic apparatus. Therefore, if there is a problem with a function of one switch assembly, it may only affect the sub-beam supplied to one lithographic apparatus, and the rest of the fabrication facility may not be affected.
  • Providing switch assemblies which operate on sub-beams may allow switch assembly configurations to be set differently for some lithographic apparatuses than for others. For example, some lithographic apparatuses may be supplied by the first radiation beam and some by the second radiation beam.
  • the switch assemblies may allow the radiation beam supplying a given lithographic apparatus to be quickly changed, minimizing the down time of that lithographic apparatus.
  • a plurality of switch assemblies may be used to switch a plurality of lithographic apparatuses (for example, all lithographic apparatuses in a facility) from sub- beams from one radiation beam to sub-beams from another radiation beam.
  • the lithographic apparatuses may be switched from sub-beams of a first radiation beam supplied by a first FEL to sub-beams of a second radiation beam supplied by a second FEL when the first FEL is going to be shut down for maintenance.
  • the switch assembly may comprise at least one reflector for reflecting at least one of the first sub-beam and the second sub-beam and/or at least one beam dump for dumping the second sub-beam in the first configuration and/or for dumping the first sub-beam in the first configuration.
  • the switch assembly may comprise at least one moveable component configured such that movement of the at least one moveable component transitions the switch assembly between the first configuration and the second configuration.
  • the movement of the at least one moveable component may comprise a translation.
  • the at least one moveable component may be mounted on rails, and the translation may comprise a translation along the rails.
  • the movement of the at least one moveable component may comprise a rotation.
  • the at least one moveable component may comprise the at least one beam dump.
  • the movement of the at least one moveable component may comprise moving the at least one beam dump from a first position in which the second sub-beam is dumped into the at least one beam dump to a second position in which the second sub-beam is dumped into the at least one beam dump.
  • the at least one beam dump may be further moveable into a third position in which both the first sub-beam and second sub-beam are dumped into the at least one beam dump.
  • the at least one moveable component may comprise the at least one reflector.
  • the switch assembly may further comprise one or more further reflectors for reflecting the first sub-beam and/or for reflecting the second sub-beam, wherein the one or more further reflectors are not part of the at least one moveable component.
  • the one or more further reflectors may be substantially static.
  • the one or more further reflectors may occupy the same position in the first configuration as in the second configuration. In some circumstances, the number of moveable parts may be minimized by using some further reflectors that are not part of the moveable assembly or moveable assemblies.
  • the at least one moveable component may comprise a single moveable unit.
  • the switch assembly may be a single moveable assembly. Transitioning from the first configuration to the second configuration may comprise moving the single moveable assembly or unit from a first position to a second position. Providing a switch that is a single moveable assembly may reduce complexity.
  • the at least one moveable component may comprise a first moveable assembly and a second moveable assembly.
  • the movement of the at least one moveable component may comprise a movement of the first moveable assembly and a different movement of the second moveable assembly.
  • the movement of the first moveable assembly may comprise a translation.
  • the movement of the second moveable assembly may comprise a translation in a different direction, for example an opposite direction, from that of the first moveable assembly.
  • the first moveable assembly may comprise the at least one beam dump and the second moveable assembly may comprise the at least one mirror.
  • the first moveable assembly and second moveable assembly may be configured such that movement of the first moveable assembly changes a path of the first sub-beam, and movement of the second moveable assembly changes a path of the second sub-beam. Movement of the first moveable assembly may not change the path of the second sub-beam. Movement of the second moveable assembly may not change the path of the first sub-beam.
  • the reflector or at least one of the reflectors, or at least one other optical component may be further configured to change the shape of the first sub-beam and/or the second sub-beam. Changing the shape of the first sub-beam and/or second sub-beam may comprise expanding the first sub-beam or second sub-beam.
  • Beam shaping may be provided within the switch assembly. Providing beam shaping within the switch assembly may reduce the amount of beam shaping required in other parts of the lithographic assembly.
  • the or each reflector may be configured to receive the first and/or second sub-beam at a grazing incidence angle.
  • the or each grazing incidence angle may be less than 20°, optionally less than 10°, further optionally less than 5°.
  • Each splitter may comprise at least one diffraction grating.
  • Each of the radiation beams may comprise extreme ultraviolet (EUV) radiation.
  • EUV extreme ultraviolet
  • the first sub-beam and the second sub-beam as received by the switch assembly may be not parallel.
  • the first sub-beam and the second sub-beam as received by the switch assembly may have a relative angle between 5° and 30°.
  • the first radiation source and the second radiation source may be spaced apart, and the system may further comprise at least one optical component configured to bring the first radiation beam and second radiation beam into closer proximity than the spacing of the first and second radiation sources before the first radiation beam and second radiation beam are received by the first and second plurality of splitters.
  • the first radiation source and the second radiation source may be spaced apart by at least 5 metres, optionally at least 10 metres.
  • the system may further comprise at least one further switch assembly, the or each further switch assembly configured to receive a respective first sub-beam which is one of the first plurality of sub-beams, receive a respective second sub-beam which is one of the second plurality of sub-beams, in a first configuration transmit the respective first sub-beam along a desired path, in a second configuration transmit the respective second sub-beam along said desired path.
  • Transmitting the first sub-beam along the desired path may comprise transmitting a part of the first sub-beam along the desired path.
  • Transmitting the second sub-beam along the desired path may comprise transmitting a part of the second sub-beam along the desired path.
  • the switch assembly may comprise a switch- splitter assembly.
  • the switch assembly may be further configured to: in the first configuration of the switch assembly, transmit a further part of the first sub-beam along a further path; and in the second configuration of the switch assembly, transmit a further part of the second sub-beam along the further path.
  • the transmitting of the further part of the first sub-beam or second sub-beam along the further path may comprise transmitting the further part of the first sub-beam or second sub-beam to a further lithographic apparatus, such that if one of the first or second sub-beam ceases to be provided, the other one of the first or second sub-beam provides radiation to the lithographic apparatus and to the further lithographic apparatus.
  • the switch assembly may be moveable to a third configuration in which the switch assembly is configured to transmit the first sub-beam along the desired path and, simultaneously, to transmit the second sub-beam along the further path.
  • a lithographic system comprising: a plurality of lithographic apparatuses; a first radiation source configured to provide a first radiation beam; at least one splitter configured to split the first radiation beam into a first plurality of sub-beams; a second radiation source configured to provide a second radiation beam; at least one further splitter configured to split the second radiation beam into a second plurality of sub-beams; and a switch assembly moveable between first and second configurations, wherein the switch assembly is configured to: receive at least one of a first sub-beam which is one of the first plurality of sub-beams and a second sub-beam which is one of the second plurality of sub-beams; in the first configuration of the switch assembly, transmit the first sub-beam to one of the plurality of lithographic apparatuses; and in the second configuration of the switch assembly, transmit the second sub-beam to said one of the plurality of lithographic apparatuses
  • Each of the plurality of lithographic apparatuses may comprise: an illumination system configured to condition a respective sub-beam received from a respective switch assembly; a support structure constructed to support a patterning device, the patterning device being capable of imparting the sub-beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table configured to hold a substrate; and a projection system configured to project the patterned radiation beam onto the substrate.
  • a switch assembly configured to: receive a first sub-beam which is one of a first plurality of sub-beams obtained by splitting a first radiation beam from a first radiation source using at least one splitter; receive a second sub-beam which is one of a second plurality of sub-beams obtained by splitting a second radiation beam from a second radiation source using at least one further splitter; in a first configuration, to transmit the first sub-beam along a desired path; and in a second configuration, to transmit the second sub-beam along said desired path.
  • the first radiation source and/or the second radiation source may comprise a free electron laser.
  • a method comprising: providing by a first radiation source a first radiation beam; providing by a second radiation source a second radiation beam; splitting by at least one splitter the first radiation beam into a first plurality of sub-beams; splitting by at least one further splitter the second radiation beam into a second plurality of sub-beams; and, using a switch assembly to: receive a first sub-beam which is one of the first plurality of sub-beams; receiving a second sub-beam which is one of the second plurality of sub-beams; in a first configuration, transmit the first sub-beam along a desired path; and in a second configuration, transmit the second sub-beam along said desired path.
  • the first radiation source and/or the second radiation source may comprise a free electron laser.
  • the switch assembly may comprise at least one moveable assembly.
  • the method may further comprise transitioning between the first configuration and the second configuration by moving the at least one moveable assembly.
  • the method may further comprise turning off the respective first and second sub- beams before moving the at least one moveable assembly.
  • the method may further comprise, before moving the at least one moveable assembly, turning off the first radiation beam and second radiation beam.
  • a system comprising: a first radiation source configured to provide a first radiation beam; at least one splitter configured to split the first radiation beam into a first plurality of sub-beams; a second radiation source configured to provide a second radiation beam; at least one further splitter configured to split the second radiation beam into a second plurality of sub-beams; and a switch assembly or mixer assembly configured to: receive a first sub-beam which is one of the first plurality of sub-beams and a second sub-beam which is one of the second plurality of sub-beams; wherein the switch assembly or mixer assembly is configured such that, if one of the first sub-beam and second sub-beam ceases to be provided, the switch assembly or mixer assembly transmits at least part of the other of the first sub-beam and second sub-beam along a desired path.
  • the first radiation source and/or the second radiation source may comprise a free electron laser.
  • the mixer assembly may be configured to transmit part of the first sub-beam and part of the second sub-beam along the desired path.
  • the mixer assembly may be configured to transmit a further part of the second sub-beam along a further path.
  • the transmitting of the part of the first sub-beam and part of the second sub-beam along the first path may comprise transmitting the first part of the first sub-beam or second part of the second sub-beam to a lithographic apparatus and the transmitting of the part of the first sub-beam and part of the second sub-beam along the second path may comprise transmitting the second part of the first sub-beam or first part of the second sub-beam to a further lithographic apparatus, such that if one of the first and second sub-beam ceases to be provided, the other one of the first or second sub-beam provides radiation to the lithographic apparatus and to the further lithographic apparatus.
  • Each of the lithographic apparatus or further lithographic apparatus may be supplied by part of the radiation from the first sub-beam and/or part of the radiation from the second sub-beam. If one of the first radiation source and second radiation source ceases to operate, the first and second lithographic apparatuses may both be driven by radiation from the other of the first radiation source and second radiation source. If the at least one splitter splitting a beam from a radiation source into a plurality of sub-beams ceases to operate, the lithographic apparatuses may be driven by radiation from the other radiation source. [0054] By providing the switch assembly or mixer assembly after the beams are split by beam splitters, a separate assembly may be provided for the sub-beams supplied to each pair of lithographic apparatuses. Therefore, if there is a problem with a function of one assembly, it may only affect the sub-beams supplied to one pair of lithographic apparatuses. The rest of the fabrication facility may not be affected.
  • the switch assembly or mixer assembly may comprise at least one grating.
  • the switch assembly or mixer assembly may comprise at least one facet mirror.
  • the mixer apparatus may not comprise moving parts.
  • the system may further comprise at least one beam shaper, wherein the at least one beam shaper is configured to shape the first sub-beam and/or second sub-beam such that the first sub-beam and/or second sub-beam has a predetermined elliptical cross section on arrival at the assembly.
  • the predetermined elliptical cross section may be such that, when output from the switch assembly or mixer assembly, a cross section of a part of the first sub-beam transmitted along the desired path substantially overlaps a cross section of a part of the second sub-beam transmitted along the desired path.
  • the at least one beam shaper may comprise, for each of the first and second sub- beam, a first beam shaper configured to change a cross section of the sub-beam from an initial elliptical cross section to a substantially circular cross section, and a second beam shaper configured to change the substantially circular cross section to the predetermined elliptical cross section.
  • the predetermined elliptical cross section may differ from the initial elliptical cross section in at least one of aspect ratio, orientation.
  • the switch assembly or mixer assembly may comprise a grating.
  • a first part of the first sub-beam and a first part of the second sub-beam may each be specularly reflected from the grating.
  • a second part of the first sub-beam and a second part of the second sub-beam may each be diffracted from the grating.
  • Each of the first sub-beam and second sub-beam may have a first diameter on exiting the at least one splitter and/or at least one further splitter.
  • the system may further comprise at least one beam expander configured to expand each of the first sub-beam and second sub-beam to a second, larger diameter on entering the assembly.
  • the switch assembly or mixer assembly may comprise a grating.
  • the assembly may be arranged such that beam-pointing errors due to wavelength shifts in the first sub-beam and/or wavelength shifts in the second sub-beam are aligned with an axis of the mixer grating that is substantially insensitive to beam-pointing angle.
  • a lithographic system comprising a plurality of lithographic apparatuses; a first radiation source configured to provide a first radiation beam; at least one splitter configured to split the first radiation beam into a first plurality of sub-beams; a second radiation source configured to provide a second radiation beam; at least one further splitter configured to split the second radiation beam into a second plurality of sub-beams; and a switch assembly or mixer assembly configured to receive a first sub-beam which is one of the first plurality of sub-beams and a second sub-beam which is one of the second plurality of sub-beams;
  • switch assembly or mixer assembly is configured such that, if one of the first sub-beam and second sub-beam ceases to be provided, the switch assembly or mixer assembly transmits at least part of the other of the first sub-beam and second sub-beam along a desired path to one of the plurality of lithographic apparatuses.
  • a switch assembly or mixer assembly configured to receive a first sub-beam which is one of a first plurality of sub-beams obtained by splitting a first radiation beam from a first radiation source using at least one splitter and a second sub-beam which is one of a second plurality of sub-beams obtained by splitting a second radiation beam from a second radiation source using at least one further splitter; wherein the switch assembly or mixer assembly is configured such that, if one of the first sub-beam and second sub-beam ceases to be provided, the switch assembly or mixer assembly transmits at least part of the other of the first sub- beam and second sub-beam along a desired path to one of the plurality of lithographic apparatuses.
  • a method comprising: providing by a first radiation source a first radiation beam; providing by a second radiation source a second radiation beam; splitting by at least one splitter the first radiation beam into a first plurality of sub-beams; splitting by at least one further splitter the second radiation beam into a second plurality of sub-beams; and, using a switch assembly or mixer assembly to receive a first sub-beam which is one of the first plurality of sub-beams and a second sub-beam which is one of the second plurality of sub- beams; wherein the switch assembly or mixer assembly is configured such that, if one of the first sub-beam and second sub-beam ceases to be provided, the switch assembly or mixer assembly transmits at least part of the other of the first sub-beam and second sub-beam along a desired path to one of the plurality of lithographic apparatuses.
  • FIG. 1 is a schematic illustration of a lithographic system according to an embodiment of the invention
  • Figure 2 is a schematic illustration of a lithographic apparatus that may form part of the lithographic system of Figure 1 ;
  • Figure 3 is a schematic illustration of a free electron laser that may form part of the lithographic system of Figure 1 ;
  • Figures 4a and 4b are schematic illustrations of a switch according to an embodiment, Figure 4a illustrating the switch in a first configuration and Figure 4b illustrating the switch in a second configuration;
  • Figures 5 a and 5b are schematic illustrations of a switch according to an embodiment, Figure 5 a illustrating the switch in a first configuration and Figure 5b illustrating the switch in a second configuration;
  • Figures 6a and 6b are schematic illustrations of a switch according to an embodiment, Figure 6a illustrating the switch in a first configuration and Figure 6b illustrating the switch in a second configuration;
  • FIGS. 7a and 7b are schematic illustrations of a switch according to an embodiment, Figure 7a illustrating the switch in a first configuration and Figure 7b illustrating the switch in a second configuration;
  • Figures 8 a and 8b are schematic illustrations of a switch according to an embodiment, Figure 8a illustrating the switch in a first configuration and Figure 8b illustrating the switch in a second configuration;
  • Figures 9 a and 9b are schematic illustrations of a switch according to an embodiment, Figure 9a illustrating the switch in a first configuration and Figure 9b illustrating the switch in a second configuration;
  • Figures 10a and 10b are schematic illustrations of a switch according to an embodiment, Figure 10a illustrating the switch in a first configuration and Figure 10b illustrating the switch in a second configuration;
  • FIGS. 10c and lOd are schematic illustrations of a switch similar to that of 10a and 10b, showing further details of implementation.
  • FIGS 11a, l ib, 11c and l id are schematic illustrations of a switch according to an embodiment, Figures 11a and l ib illustrating the switch in a first configuration and Figures 11c and l id illustrating the switch in a second configuration;
  • Figures 12a and 12b are schematic illustrations of a switch according to an embodiment, Figure 12a illustrating the switch in a first configuration and Figure 12b illustrating the switch in a second configuration;
  • Figures 13a and 13b are schematic illustrations of a switch according to an embodiment, Figure 13a illustrating the switch in a first configuration and Figure 13b illustrating the switch in a second configuration;
  • FIG. 14 is a schematic illustration of a lithography system in which two FELs each drive N scanners;
  • Figure 15 is a schematic illustration of a lithography system in which a switch-splitter connects 2 FELs to 2N scanners;
  • Figure 16 is a schematic illustration of three states of a switch-splitter
  • FIG. 17 is a schematic illustration of a lithography system in accordance with an embodiment, in which two FELs serve N scanners;
  • Figure 18 is a schematic illustration of two states of a switch
  • Figure 19 is a schematic illustration of a lithography system in accordance with a further embodiment, in which two FELs serve N scanners;
  • FIG. 20 is a schematic illustration of a combiner
  • FIG. 21 is a schematic illustration of a lithography system in accordance with an embodiment, in which two FELs serve N scanners using 3-state switch-splitters;
  • Figure 22 is a schematic illustration of three states of a switch-splitter
  • Figure 23 is a schematic illustration of a lithography system in accordance with an embodiment, in which two FELs serve N scanners using mixers;
  • Figure 24 is a schematic illustration of a mixer
  • Figure 25 is a schematic illustration of a top view of a grating-based mixer
  • Figure 26 is a schematic illustration of a single facet mirror
  • Figure 27 is a schematic illustration of a mixer based on facet mirrors
  • Figure 28 is a schematic illustration of a mixer grating with input beams of circular cross-section, resulting in mixed output beams
  • Figure 29 is a schematic illustration of a symmetric mixer layout
  • Figure 30 is a schematic illustration of input-beam angles for a splitter/mixer grating
  • - Figure 31 is a schematic illustration of a beam path from an FEL to a litho scanner, in which squares next to the beam indicate the cross-section at various locations;
  • Figure 32 is a schematic illustration of beam parameters for a symmetric 3-way splitter grating.
  • FIG 1 shows a lithographic system LS according to one embodiment of the invention.
  • the lithographic system LS comprises a plurality of lithographic apparatuses LA a - LA n (e.g. ten lithographic apparatuses), of which three LA a , LA b , LA n are shown in Figure 1.
  • the lithographic system LS comprises two radiation sources 30 and 40 which are each configured to provide extreme ultraviolet (EUV) radiation to the lithographic apparatuses.
  • Radiation source 30 is configured to generate a first EUV radiation beam RB 1 (which may be referred to as a first main beam).
  • Radiation source 40 is configured to generate a second EUV radiation beam RB2 (which may be referred to as a second main beam).
  • each of the radiation sources 30 and 40 comprises a free electron laser (FEL).
  • FEL free electron laser
  • the first radiation beam RB I from the first FEL 30 is passed through an EUV- reflective mirror 31 that separates gamma radiation from EUV radiation, hereinafter called a gamma mirror 31.
  • a gamma mirror 31 that separates gamma radiation from EUV radiation
  • the radiation beam RB 1 is passed through a beam shaper 32.
  • Beam shaper 32 may comprise beam expanding optics that are arranged to increase a cross section of the main radiation beam RB.
  • this may decrease the heat load on mirrors downstream of the beam shaper 32, for example mirrors within the lithographic apparatus LA a -LA n .
  • This may allow these mirrors to be of a lower specification, with less cooling, and therefore less expensive. Additionally or alternatively, it may allow the downstream mirrors to be nearer to normal incidence.
  • the lithographic system LS may further comprise one or more further beam shapers, for example beam shapers comprising beam expanding optics that are arranged to increase a cross-section of branch radiation beams B a -B n .
  • beam shaper 32 may be positioned further upstream or downstream than in the embodiment of Figure 1.
  • Radiation beam RBI is then passed into a splitter assembly 33.
  • the splitter assembly 33 splits the first radiation beam RB I into a plurality of sub-beams SBl a -SB l n , one sub-beam for each of the plurality of lithographic apparatuses LA a -LA n .
  • the splitter assembly 33 comprises a plurality of splitters, each splitting off at least one respective sub-beam. Any appropriate splitters may be used.
  • each splitter comprises at least one diffraction grating. For gratings, one may split off the +1 order and -1 order diffracted beams and lead the 0* order beam to the next grating. However, in some of the diagrams below, the splitting off of only one beam is illustrated, for clarity of illustration.
  • Grazing incidence diffraction gratings are used to separate radiation beam RB 1 into the plurality of sub-beams SB l a -SBl n .
  • the splitters are shown as being part of a splitter assembly 33, in other embodiments the splitters may be discrete components.
  • the lithographic system may comprise a plurality of splitters, each splitting off one or more sub-beams from the main beam. For example, each splitter may split off a first sub-beam having an upwards trajectory with respect to the main beam, and a second sub-beam having a downwards trajectory with respect to the main beam.
  • the second radiation beam RB2 from the second FEL undulator 40 is passed through a gamma mirror 41 , through a beam shaper 42, and into a splitter assembly 43.
  • the splitter assembly 43 splits the second radiation beam RB2 into a plurality of radiation sub- beams SB2 a -SB2 n , one for each lithographic apparatus LA a -LA n .
  • Each of FEL 40, gamma mirror 41 , beam shaper 42 and splitter assembly 43 may be as described above with reference to the corresponding components for the first radiation beam (i.e. FEL 30, gamma mirror 31 , beam shaper 32 and splitter assembly 33).
  • splitter assemblies 33 and 43 are illustrated as being straight, in reality they may be curved, since each beam- splitting grating may deflect the beam by a small angle.
  • the lithographic system LS further comprises a plurality of switches 50a to 50n, one for each of the plurality of lithographic apparatuses LA a -LA n .
  • Each switch is configured to receive one sub-beam from the first radiation beam and one sub-beam from the second radiation beam.
  • Each switch is configured to output one of its received sub-beams to its corresponding lithographic apparatus, and to dump the other of its received sub-beams into a beam dump.
  • Each switch may comprise at least one beam dump. These beam dumps may be in addition to the beam dump 27 which is described below with reference to Figure 3, and is used to dump electrons.
  • each switch The beam dumps that are part of each switch are required to dump an EUV sub-beam (which may be a EUV beam having a power higher than 1 kW) if it is not used.
  • the beam dump(s) of each switch may comprise any suitable material.
  • each beam dump in a switch comprises copper. Copper may be used because of its excellent thermal conductivity.
  • each beam dump in a switch comprises copper with a suitable surface treatment for vacuum compatibility and improved EUV absorption.
  • switch 50a receives sub-beams SBl a from splitter assembly 33 and receives sub-beam SB2 a from splitter assembly 43.
  • Switch 50a transmits one of sub-beam SBl a and sub-beam SB2 a to the first lithographic apparatus LA a .
  • Switch 50a dumps the other of sub-beam SB l a and sub-beam SB2 a into a beam dump.
  • the transmitted sub-beam may be called a branch radiation beam, and may be designated B a .
  • switch 50b receives sub-beams SB l and SB2 b , and transmits one of SB l and SB2 b to lithographic apparatus LA b while dumping the other of SB l b or SB2 b into a beam dump.
  • the transmitted sub-beam from switch 50b is designated as branch radiation beam B b .
  • Each of the switches 50a-50n outputs a respective branch radiation beam B a -B n along a respective desired path to a respective lithographic apparatus LA a -LA n .
  • Each branch radiation beam B a -B n may be either a sub-beam SB l a -SBl n of the first radiation beam RBI, or a sub-beam SB2 a -SB2 n of the second radiation beam RB2, depending on the position of each switch 50a to 50n.
  • all the lithographic apparatuses LA a -LA n may receive radiation sub-beams from the same radiation source.
  • switches 50a to 50n may be configured so as to transmit radiation sub-beams SB l a to SBl n from the first radiation source 30.
  • different lithographic apparatuses LA a -LA n may receive radiation sub-beams from different radiation sources.
  • switch 50a may be broken such that lithographic apparatus LA a can only use the radiation from splitter 43 (originating from radiation beam RB2), whereas at the same time some optics in the splitter are broken such that only the beam SB2 n is available to switch 50n.
  • Other lithographic apparatuses may be operated using sub-beams from radiation beam RB 1.
  • each branch radiation beam B a -B n is passed through a respective bender 51a-51n.
  • the purpose of each bender 51a-51n is to turn the beam upwards.
  • each radiation source 30, 40 is arranged such that each main radiation beam RBI, RB2 propagates generally horizontally.
  • Each lithographic apparatus LA a -LA n is arranged to accept a branch radiation beam B a -B n that propagates in a generally vertical direction. Therefore, benders 51a-51n are arranged to bend each branch radiation beam B a -B n so as to change its direction from a generally horizontal to a generally vertical direction using bending optics.
  • the bending optics of each bender 51a-51n may comprise a plurality of grazing incidence mirrors that are collectively arranged to bend a branch radiation beam through an angle of around 90°.
  • the branch radiation beams B a -B n are each directed through a respective attenuator 52a to 52n.
  • Each attenuator 52a to 52n is arranged to adjust the intensity of a respective branch radiation beam B a -B n before the branch radiation beam B a -B n passes into its corresponding lithographic apparatus LA a -LA n .
  • Each attenuator 52a to 52n may reduce the intensity of its respective branch radiation beam B a -B n to compensate for fluctuations in intensity.
  • each branch radiation beam B a -B n is passed through a respective scanner delivery system 53a to 53n.
  • the scanner delivery system 53a- 53n may comprise suitable directing mirrors and/or a beam expander.
  • the scanner delivery system 53a-53n may be configured to make the branch radiation beam B a -B n that is delivered to each lithographic apparatus LA a -LA n have similar properties to a radiation beam that may be received from a laser-produced plasma (LPP source).
  • the radiation beam may be matched in terms of intermediate focus (IF) size, etendue at IF, and angular distribution of the light after IF.
  • each lithographic apparatus LA a -LA n is capable of receiving radiation from either an FEL radiation source or an LPP radiation source.
  • each lithographic apparatus LA a -LA n comprises a respective scanner.
  • An example of a lithographic apparatus is described below with reference to Figure 2.
  • lithographic system LS may be constructed and arranged such that they can be isolated from the external environment.
  • a vacuum may be provided in at least part of the lithographic system LS so as to minimise the absorption of EUV radiation.
  • Different parts of the lithographic system LS may be provided with vacuums at different pressures (i.e. held at different pressures which are below atmospheric pressure).
  • the vacuum environment that contains the reflective surface of the mirrors may be isolated from the environment of the actuators and sensors, for the purposes of eliminating sources of contamination. Having one atmosphere of pressure difference between the front and back of a mirror may be undesirable.
  • One possible implementation is to have some parts of some components (for example, actuators and sensors) encapsulated in a vacuum box inside a clean vacuum environment.
  • two radiation sources are provided, and switches are provided that select for each lithographic apparatus either a sub-beam from the first radiation source, or a sub-beam from the second radiation source.
  • the switches are positioned after the splitter apparatus 33. Therefore, the switches operate at the level of the sub-beams rather than at the level of the main radiation beams RB 1 , RB2.
  • the embodiment of Figure 1 may provide fast switching of EUV radiation delivered by different FELs, where the switching is operated on a per-apparatus basis.
  • the time taken to switch from one sub-beam to another may be far less than the start-up time of an FEL.
  • a fault in the switch could result in no radiation beam being provided to any of the lithographic apparatuses.
  • the switch may act as a single point of failure. By positioning the switch after the splitter assembly 33, a fault in a switch (or a fault in a splitter) may stop only one scanner from operating.
  • the embodiment of Figure 1 provides two radiation sources with the ability to select which of the radiation sources provides radiation to each lithographic apparatus on a per- apparatus basis. By providing more than one radiation source, redundancy may be added to the system. If one FEL is to go offline, for example for scheduled maintenance, the other FEL may be brought into operation. In some circumstances, the other FEL may be brought into operation with very little down-time. For example, if a component (for example, a component of a FEL) breaks unexpectedly then it may be necessary to bring the other FEL into operation quickly. Having the switch beyond the splitters may reduce single points of failure. Single points of failure may lead to multiple scanners being down as a result of a single failure.
  • a component for example, a component of a FEL
  • each switch operates to select between a sub-beam from the first radiation source and a sub-beam from the second radiation source.
  • more than two radiation sources may be provided.
  • each switch may select between more than two sub-beams.
  • FIG. 2 shows a lithographic apparatus LA a , which comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS and a substrate table WT configured to support a substrate W.
  • the illumination system IL is configured to condition the branch radiation beam B a that is received by that lithographic apparatus LA a before it is incident upon the patterning device MA.
  • the projection system PS is configured to project the radiation beam B a ' (now patterned by the patterning device MA) onto the substrate W.
  • the substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus aligns the patterned radiation beam B a ' with a pattern previously formed on the substrate W.
  • the branch radiation beam B a that is received by the lithographic apparatus LA a passes into the illumination system IL from the scanner delivery system 53a though an opening 8 in an enclosing structure of the illumination system IL.
  • the branch radiation beam B a is focused to form an intermediate focus 9 at or near to the opening 8.
  • the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11.
  • the faceted field mirror device 10 and faceted pupil mirror device 11 together provide the radiation beam B a with a desired cross-sectional shape and a desired angular distribution.
  • the radiation beam B a passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT.
  • the patterning device MA reflects and patterns the radiation beam to form a patterned beam B a '.
  • the illumination system IL may include other mirrors or devices in addition to or instead of the faceted field mirror device 10 and faceted pupil mirror device 11.
  • the illumination system IL may for example include an array of independently moveable mirrors.
  • the independently moveable mirrors may for example measure less than 1mm across.
  • the independently moveable mirrors may for example be microelectromechanical systems (MEMS) devices.
  • MEMS microelectromechanical systems
  • the projection system PS comprises a plurality of mirrors 13, 14 which are configured to project the radiation beam B a ' onto a substrate W held by the substrate table WT.
  • the projection system PS may apply a reduction factor to the radiation beam, forming an image with features that are smaller than corresponding features on the patterning device MA. A reduction factor of 4 may for example be applied.
  • the projection system PS has two mirrors in Figure 2, the projection system may include any number of mirrors (e.g. six mirrors).
  • the lithographic apparatus LA a is operable to impart a radiation beam B a with a pattern in its cross-section and project the patterned radiation beam onto a target portion of a substrate thereby exposing a target portion of the substrate to the patterned radiation.
  • the lithographic apparatus LA a may, for example, be used in a scan mode, wherein the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B a ' is projected onto a substrate W (i.e. a dynamic exposure).
  • the velocity and direction of the substrate table WT relative to the support structure MT may be determined by the demagnification and image reversal characteristics of the projection system PS.
  • the patterned radiation beam B a ' which is incident upon the substrate W may comprise a band of radiation.
  • the band of radiation may be referred to as an exposure slit.
  • the movement of the substrate table WT and the support structure MT are such that the exposure slit travels over a target portion of substrate W in a scan direction, thereby exposing the target portion of the substrate W to patterned radiation.
  • a dose of radiation to which a given location within the target portion of the substrate W is exposed depends on the power of the radiation beam B a ' and the amount of time for which that location is exposed to radiation as the exposure slit is scanned over the location (the effect of the pattern is neglected in this instance).
  • the term "target location” may be used to denote a location on the substrate which is exposed to radiation (and for which the dose of received radiation may be calculated).
  • Figure 3 is a schematic depiction of a free electron laser FEL comprising an injector 21, a linear accelerator 22, a bunch compressor 23, an undulator 24, an electron decelerator 26 and a beam dump 27.
  • the free electron laser FEL may be, for example, radiation source 30 or 40 of the lithographic system of Figure 1.
  • the injector 21 is arranged to produce a bunched electron beam E and may comprise an electron source and an electron beam chopper.
  • the electron source may, for example, comprise a thermionic cathode or a photo-cathode arranged to emit electrons and an accelerating electric field arranged to accelerate said electrons so as to form an electron beam.
  • the linear accelerator 22 may comprise a plurality of radio frequency cavities, which are axially spaced along a common axis, and one or more radio frequency power sources, which are operable to control the electromagnetic fields along the common axis as bunches of electrons pass between them so as to accelerate each bunch of electrons.
  • the cavities may be superconducting radio frequency cavities.
  • this allows: relatively large electromagnetic fields to be applied at high duty cycles; larger beam apertures, resulting in fewer losses due to wakefields; and for the fraction of radio frequency energy that is transmitted to the beam (as opposed to dissipated through the cavity walls) to be increased.
  • the cavities may be conventionally conducting (i.e. not superconducting), and may be formed from, for example, copper.
  • linear accelerators may be used such as, for example, laser wake-field accelerators or inverse free electron laser accelerators.
  • the electron beam E passes through a bunch compressor 23, disposed between the linear accelerator 22 and the undulator 24.
  • the bunch compressor 23 is configured to spatially compress existing bunches of electrons in the electron beam E.
  • One type of bunch compressor 23 comprises a radiation field directed transverse to the electron beam E. An electron in the electron beam E interacts with the radiation and bunches with other electrons nearby.
  • Another type of bunch compressor 23 comprises a magnetic chicane, wherein the length of a path followed by an electron as it passes through the chicane is dependent upon its energy.
  • This type of bunch compressor may be used to compress bunches of electrons which have been accelerated in a linear accelerator 22 by a plurality of resonant cavities.
  • the electron beam E then passes through the undulator 24.
  • the undulator 24 comprises a plurality of modules.
  • Each module comprises a periodic magnet structure, which is operable to produce a periodic magnetic field and is arranged so as to guide the relativistic electron beam E produced by the injector 21 and linear accelerator 22 along a periodic path within that module.
  • the periodic magnetic field produced by each undulator module causes the electrons to follow an oscillating path about a central axis.
  • the electrons radiate electromagnetic radiation generally in the direction of the central axis of that undulator module.
  • the path followed by the electrons may be sinusoidal and planar, with the electrons periodically traversing the central axis.
  • the path may be helical, with the electrons rotating about the central axis.
  • the type of oscillating path may affect the polarization of radiation emitted by the free electron laser.
  • a free electron laser which causes the electrons to propagate along a helical path may emit elliptically polarized radiation, which may be desirable for exposure of a substrate W by some lithographic apparatus.
  • each undulator module As electrons move through each undulator module, they interact with the electric field of the radiation, exchanging energy with the radiation. In general the amount of energy exchanged between the electrons and the radiation will oscillate rapidly unless conditions are close to a resonance condition. Under resonance conditions, the interaction between the electrons and the radiation causes the electrons to bunch together into microbunches, modulated at the wavelength of radiation within the undulator, and coherent emission of radiation along the central axis is stimulated.
  • the resonance condition may be given by:
  • X em is the wavelength of the radiation
  • X u is the undulator period for the undulator module that the electrons are propagating through
  • ⁇ is the Lorentz factor of the electrons
  • K is the undulator parameter.
  • each bunch of electrons will have a spread of energies although this spread may be minimized as far as possible (by producing an electron beam E with low emittance).
  • the undulator parameter K is typically approximately 1 and is given by:
  • the resonant wavelength X em is equal to the first harmonic wavelength spontaneously radiated by electrons moving through each undulator module.
  • the free electron laser FEL may operate in self-amplified spontaneous emission (SASE) mode. Operation in SASE mode may require a low energy spread of the electron bunches in the electron beam E before it enters each undulator module.
  • the free electron laser FEL may comprise a seed radiation source, which may be amplified by stimulated emission within the undulator 24.
  • the free electron laser FEL may operate as a recirculating amplifier free electron laser (RAFEL), wherein a portion of the radiation generated by the free electron laser FEL is used to seed further generation of radiation.
  • RAFEL recirculating amplifier free electron laser
  • Electrons moving through the undulator 24 may cause the amplitude of radiation to increase, i.e. the free electron laser FEL may have a non-zero gain. Maximum gain may be achieved when the resonance condition is met or when conditions are close to but slightly off resonance.
  • the undulator 24 may be tapered. That is, the amplitude of the periodic magnetic field and/or the undulator period u may vary along the length of the undulator 24 in order to keep bunches of electrons at or close to resonance as they are guided though the undulator 24.
  • the tapering may be achieved by varying the amplitude of the periodic magnetic field and/or the undulator period X u within each undulator module and/or from module to module. Additionally or alternatively tapering may be achieved by varying the helicity of the undulator 24 (by varying the parameter A) within each undulator module and/or from module to module.
  • a region around the central axis of each undulator module may be considered to be a "good field region".
  • the good field region may be a volume around the central axis wherein, for a given position along the central axis of the undulator module, the magnitude and direction of the magnetic field within the volume are substantially constant.
  • An electron bunch propagating within the good field region may satisfy the resonant condition of Eq. (1) and will therefore amplify radiation. Further, an electron beam E propagating within the good field region should not experience significant unexpected disruption due to uncompensated magnetic fields. That is, an electron propagating through the good field region should remain within the good field region.
  • Each undulator module may have a range of acceptable initial trajectories. Electrons entering an undulator module with an initial trajectory within this range of acceptable initial trajectories may satisfy the resonant condition of Eq. (1) and interact with radiation in that undulator module to stimulate emission of coherent radiation. In contrast, electrons entering an undulator module with other trajectories may not stimulate significant emission of coherent radiation.
  • the electron beam E should be substantially aligned with the central axis of the undulator module.
  • a tilt or angle between the electron beam E and the central axis of the undulator module (in radians) should generally not exceed p/10, where p is the FEL Pierce parameter. Otherwise the conversion efficiency of the undulator module (i.e. the portion of the energy of the electron beam E which is converted to radiation in that module) may drop below a desired amount (or may drop almost to zero).
  • the FEL Pierce parameter of an EUV helical undulator module may be of the order of 0.001, indicating that the tilt of the electron beam E with respect to the central axis of the undulator module should be less than 100 ⁇ rad.
  • a greater range of initial trajectories may be acceptable.
  • the electron beam E remains substantially perpendicular to the magnetic field of a planar undulator module and remains within the good field region of the planar undulator module, coherent emission of radiation may be stimulated.
  • the electrons of the electron beam E move through a drift space between each undulator module, the electrons do not follow a periodic path. Therefore, in this drift space, although the electrons overlap spatially with the radiation, they do not exchange any significant energy with the radiation and are therefore effectively decoupled from the radiation.
  • the bunched electron beam E has a finite emittance and will therefore increase in diameter unless refocused.
  • the undulator 24 may further comprise a mechanism for refocusing the electron beam E in between one or more pairs of adjacent undulator modules.
  • a quadrupole magnet may be provided between each pair of adjacent modules. The quadrupole magnets reduce the size of the electron bunches. This improves the coupling between the electrons and the radiation within the next undulator module, increasing the stimulation of emission of radiation.
  • the undulator 24 may further comprise an electron beam steering unit in between each adjacent pair of undulator modules which is arranged to provide fine adjustment of the electron beam E as it passes through the undulator 24.
  • each beam steering unit may be arranged to ensure that the electron beam remains within the good field region and enters the next undulator module with a trajectory from the range of acceptable initial trajectories for that undulator module.
  • the beam steering unit may include a transverse beam position sensor.
  • Radiation produced within the undulator 24 is output as a radiation beam BFEL (which may, for example, correspond to the first radiation beam RB I or second radiation beam RB2 of Figure 1).
  • the electron beam E is absorbed by a dump 27.
  • the dump 27 may comprise a sufficient quantity of material to absorb the electron beam E.
  • the material may have a threshold energy for induction of radioactivity. Electrons entering the dump 27 with an energy below the threshold energy may produce only gamma ray showers but will not induce any significant level of radioactivity.
  • the material may have a high threshold energy for induction of radioactivity by electron impact.
  • the beam dump may comprise aluminium (Al), which has a threshold energy of around 17 MeV. It may be desirable to reduce the energy of electrons in the electron beam E before they enter the dump 27. This removes, or at least reduces, the need to remove and dispose of radioactive waste from the dump 27.
  • the energy of electrons in the electron beam E may be reduced before they enter the dump 27 by directing the electron beam E through a decelerator 26 disposed between the undulator 24 and the beam dump 27.
  • the electron beam E which exits the undulator 24 may be decelerated by passing the electrons back through the linear accelerator 22 with a phase difference of approximately 180 degrees relative to the electron beam produced by the injector 21.
  • the RF fields in the linear accelerator therefore serve to decelerate the electrons which are output from the undulator 24 and to accelerate electrons output from the injector 21.
  • Such an arrangement is known as an energy recovery linear accelerator (ERL).
  • switches 50a-50n are each configured to receive a pair of sub-beams (one from the first radiation beam RB 1 and one from the first second radiation beam RB2), to transmit one of the pair of sub-beams to a lithographic apparatus, and to dump the other of the pair of sub-beams.
  • switches 50a-50n may comprise a switch assembly as described below with reference to any of Figures 4a to 13b.
  • switches may be used for different switches in the lithographic system of Figure 1.
  • different pairs of sub-beams may enter their respective switches at different relative angles. Therefore, switches may be designed differently to accommodate the different angles of incidence.
  • the angle between sub-beams SB l a and SB2 a on entering switch 50a is around 26°, while the angle between sub-beams SBl n and SB2 n on entering switch 50n is around 6°.
  • sub-beams are parallel on entering at least one of the switches.
  • FIGs 4a and 4b illustrate a switch assembly 50a which is configured to receive two sub-beams SB l a and SB2 a , to transmit one of the sub-beams (SBl a or SB2 a ) along a desired path, and to dump the other of the sub-beams (SB2 a or SB l a ).
  • the switch assembly 50a dumps the first sub-beam SBl a and transmits the second sub-beam SB2 a .
  • the switch assembly 50a transmits the first sub-beam SBl a along the desired path and dumps the second sub-beam SB2 a .
  • the radiation sub-beams SB l a , SB2 a are substantially parallel on entering the switch assembly.
  • the radiation sub- beams propagate horizontally from the left of the figure.
  • Switch assembly 50a comprises a first moveable part comprising two beam dumps 60 and 61, and a second moveable part 62 comprising mirrors 63, 64, 65 and 66.
  • the second moveable part 62 may also be referred to as a mirror assembly 62.
  • Each moveable part is moveable along an axis that is substantially perpendicular to the direction of travel of the incident sub-beams. As viewed in Figures 4a and 4b, each axis of movement is vertical, and the axes of movement of the two moveable parts are parallel to each other.
  • each moveable part is mounted on a respective set of rails. In other embodiments, moveable parts may have axes of movement that are not parallel to each other.
  • the first moveable part is translated upwards along its axis of movement (as viewed in Figures 4a and 4b) and the second moveable part 62 is translated downwards along its axis of movement.
  • the first moveable part is translated downwards and the second moveable part 62 is translated upwards.
  • Beam dumps 60 and 61 are spaced apart along their axis of movement, with a spacing that may be comparable to the spacing between the two sub-beams.
  • beam dump 60 is positioned in front of sub-beam SBl a , causing sub-beam SB l a to be dumped into beam dump 60.
  • Beam dump 61 is positioned such that it is offset from sub-beam SB2 a and does not block sub-beam SB2 a .
  • Sub-beam SB2 a passes into the mirror assembly 62 and is incident on mirror 66.
  • Sub-beam SB2 a is reflected from mirror 66 at a grazing incidence angle and is incident on mirror 65.
  • Sub-beam SB2 a is reflected from mirror 65 at a grazing incidence angle.
  • Each grazing incidence angle may be a grazing incidence angle of less than 4° (in a convention in which 0° is along the plane of the mirror surface). In some embodiments, each grazing incidence angle may be a grazing incidence angle of less than 20°.
  • Each of the additional embodiment below may also use mirrors that reflect the sub- beams at a grazing incidence angle of below 4°, or below 20°. The range of incidence angles used may be considered as a trade-off. Small grazing incidence angles may require larger (and more expensive) optics, but may have less absorption loss. EUV absorptance may be approximately 1.2% per degree of grazing angle. In some embodiments, angles can be defined for other reasons, such as what fits in the fab and/or what is preferred with respect to polarization equality for all scanners.
  • Sub-beam SB2 a exits the mirror assembly 62 in a horizontal direction propagating from left to right in Figure 4a. At this point, sub-beam SB2 a may be referred to as branch radiation beam B a , which is the output of switch assembly 50a.
  • the direction of branch radiation beam B a is substantially parallel to that of sub- beams SB l a , SB2 a , but is offset vertically from the original axis of sub-beam SB2 a due to its reflection from mirrors 66 and 65.
  • the beam dumps 60, 61 are translated upwards and the mirrors 63, 64, 65, 66 is translated downwards.
  • Any appropriate method of moving each moveable part may be used.
  • a two step approach to movement is used.
  • a first step comprises coarse large movements between two end stops, and a second step comprises fine movement of the mirrors as part of the control loop of the entire beam path.
  • beam dump 61 is positioned in front of sub-beam SB2 a , causing sub-beam SB2 a to be dumped into beam dump 61.
  • Beam dump 60 is positioned such that it is offset from sub-beam SBl a and does not block sub-beam SBl a .
  • Sub-beam SB l a passes into the mirror assembly 62 and is incident on mirror 63.
  • Sub- beam SBl a is reflected from mirror 63 at a grazing incidence angle and is incident on mirror 64.
  • Sub-beam SBl a is reflected from mirror 64 at a grazing incidence angle.
  • Sub-beam SB l a exits the mirror assembly 62 in a horizontal direction propagating from left to right in Figure 4a. At this point, sub-beam SB l a may be referred to as branch radiation beam B a , which is the output of switch assembly 50a.
  • beam dumps 60 and 61 are each illustrated as having a surface perpendicular to the incident beams SB l a and SB2 a . However, in practice, beam dumps 60 and 61 may be arranged at grazing incidence to spread out the heat dump. Similar comments apply to the beam dumps illustrated in the schematic drawings of Figures 5a to 13b.
  • the position of branch radiation beam B a is the same in the second configuration as in the first configuration. In the first configuration, branch radiation beam B a results from sub-beam SB2 a being translated upwards by mirrors 66 and 65. In the second configuration, branch radiation beam B a results from sub-beam SBl a being translated downwards by mirrors 63 and 64.
  • the radiation supplied to the lithographic apparatus by each sub-beam may be in nominally the same polarization state.
  • the grazing angles and the orientations of the planes of incidence relative to the preceding mirror should also be matched.
  • At least part of the switch assembly 50a may be within a vacuum.
  • the mirrors 63, 64, 65, 66 may be provided within a vacuum.
  • some or all components of the switch assembly 50a are moveable within a vacuum. In other embodiments, some or all of the components of switch assembly 50a are moveable outside a vacuum.
  • the radiation beams RBI and RB2 (and therefore the sub-beams SBl a and SB2 a ) are turned off before the switch assembly 50a is operated (i.e. before either moveable part of the switch assembly is moved 50a).
  • the beams may be switched off for safety.
  • the beams may be switched off to avoid the possibility of any damage to the mirrors, for example damage resulting from a side of the mirror other than the reflective surface being hit by EUV radiation.
  • the moveable parts are each moved to the desired configuration (for example, moved from the first configuration of Figure 4a to the second configuration of Figure 4b).
  • radiation beams RB I and RB2 may be turned on again.
  • the radiation beams RB I and RB2 may not be turned off before the switch assembly is operated.
  • beam dumps 60 and 61 are designed to allow for at least one further configuration (not shown) in which sub-beam SB l a is dumped into dump 60 at the same time as SB2 a is dumped into dump 61.
  • the first moveable part may be moveable to a third position along its moveable axis in which each beam dump blocks its respective sub-beam. The third position may be a position between the first position used for the first configuration and the second position used for the second configuration.
  • the first moveable part and second moveable part begin in their first configurations.
  • the first moveable part (comprising the beam dumps) is moved into its third position (both sub-beams dumped) so that there may be no risk of the radiation damage to the mirrors while the mirrors are being moved.
  • the mirror assembly 62 is moved from its first configuration to its second configuration by translation downwards.
  • the beam dumps 60, 61 are then moved into their second configuration by translation upwards, allowing sub-beam SB2 a to pass into the mirror assembly 62.
  • beam dumps 60 and 61 may be moved independently. Beam dumps 60 and 61 may be moved quickly and sequentially when switching between beams. For example, when switching from the first configuration of Figure 4a to the second configuration of Figure 4b, beam dump 61 may be inserted so that both beams are dumped, and then beam dump 40 may be removed.
  • An EUV beam hitting an edge of a beam dump may scatter radiation in undesired directions and/or cooling may not work well.
  • Dumping both sub-beams and passing neither sub-beam to the scanner may allow for maintenance in the beam path after the switch.
  • At least one additional beam dump is used to dump both sub-beams before any movement of switch components starts.
  • at least one additional beam dump blocks either or both of the main beams RBI , RB2.
  • at least one additional beam dump blocks either or both of sub-beams SBl a , SB2 a after they leave the splitter assembly 33, 34 but before they enter the switch assembly 50a.
  • everything is designed so that both FEL beams are disabled (or dumped into a big beam dump) directly at the FEL undulator before any beam switch is activated. Disabling or dumping both FEL beams at the FEL undulator before activation of a beam switch may cost some alignment or warm-up time.
  • the radiation sub-beams must be turned off before moving components of the switch, for example by turning off the FEL sources 30, 40 or by using an additional beam dump to block both sub-beams.
  • beam dump components of the switch itself may be used to block both sub- beams before other components of the switch (for example, mirrors) are moved from one configuration to another.
  • the mirrors are moved separately from the beam dump(s).
  • the beam dump or beam dumps may be moved quickly, for example to minimize the time that an EUV beam strikes the edge of a beam dump.
  • the mirror assembly may be moved more slowly. Precision of the movement of the mirrors may be more important than speed.
  • Figures 5a and 5b illustrate another embodiment of a switch assembly 50a, in which the incoming sub-beams are non-parallel.
  • the switch assembly 50a comprises translating mirrors 72, 73, 74 and 75 and a translating beam dump 71.
  • the single beam dump 71 may be replaced with a plurality of beam dumps.
  • all the mirrors 72, 73, 74, 75 and the beam dump 71 are part of a single moveable assembly 70.
  • Switching the switch assembly 50a between a first configuration ( Figure 5 a) and a second configuration (Figure 5b) comprises translating the moveable assembly 70 vertically.
  • the moveable assembly 70 may be mounted on rails.
  • sub-beam SB l a enters the switch assembly 50a diagonally from the top left
  • sub-beam SB2 a enters the switch assembly 50a diagonally from the bottom left.
  • the switch assembly it may be preferable to have sub- beams entering the switch assembly at a relative angle than to make the sub-beams parallel before they enter the switch assembly.
  • Free electron lasers tend to be large and if placed side by side may be separated by metres, for example by 10 metres.
  • Mirrors may be used to bend the radiation beams that issue from the free electron lasers so that they become closer together, resulting in the radiation beams propagating at a relative angle. It may be more convenient to provide a switch assembly that accepts incoming sub-beams at a relative angle than to make the sub-beams parallel before they enter the switch assembly.
  • the free electron lasers are placed at a relative angle to each other, and radiation beams RB I and RB2 propagate at that relative angle.
  • the resulting sub- beams may also propagate at a relative angle to each other, which may be different from the original relative angle of the FELs.
  • different switches receive sub- beams at different angles. In some embodiments, different switches receive sub-beams at the same angle.
  • Switch assembly 50a comprises a moveable assembly 70 which comprises the beam dump 71 and the four bending mirrors 72, 73, 74 and 75.
  • a first configuration of switch assembly 50a is illustrated in Figure 5a.
  • beam dump 71 is positioned in front of sub-beam SB2 a and not in front of sub-beam SB l a .
  • Sub-beam SB l a is bent by mirrors 72 and 73 (each of which reflects sub-beam SBl a at a grazing incidence angle) to provide a horizontal output beam B a .
  • the moveable assembly 70 is translated upwards.
  • the beam dump 71 is positioned in front of sub-beam SB l a and not in front of sub-beam SB2 a .
  • Sub- beam SB2 a is bent by mirrors 74 and 75 to provide a horizontal output beam B a .
  • the horizontal output beam B a has the same position in the first configuration as in the second configuration.
  • sub-beam SBl a entering diagonally from the top right is bent upwards such that it is horizontal.
  • sub-beam SB l a entering diagonally from the bottom right is bent downwards such that it is horizontal.
  • two mirrors 72 and 73 or 74 and 75 are used to bend the selected sub-beam to the required output direction.
  • one mirror is used to bend the selected sub-beam, or more than two mirrors are used to bend the selected sub-beam.
  • the number of mirrors used may depend on the angle to which the sub-beam may be bent, and/or on the angle of reflection at which each mirror may be operated.
  • FIGS 6a and 6b illustrate a further embodiment of a switch assembly 50a in which the incoming sub-beams are non-parallel and crossing.
  • Sub-beam SB l a enters the switch assembly 50a diagonally from the top left of the figures
  • SB2 a enters the switch assembly 50a diagonally from the bottom left.
  • the paths of SBl a and SB2 a cross before SB l a or SB2 a enters the switch assembly 50a.
  • Switch assembly 50a comprises translating mirrors 82, 83, 84, 85 and a translating beam dump 81 (which in other embodiments may be a plurality of beam dumps), which form part of a single moveable assembly 80.
  • Figure 6a illustrates a first configuration of switch assembly 50a in which beam dump 81 is in front of sub-beam SBl a and not in front of sub-beam SB2 a .
  • Sub-beam SB2 a reflects from mirrors 82 and 83, which together translate the sub-beam vertically and bend its direction of travel to horizontal.
  • Sub-beam SB2 a is output as branch radiation beam B a .
  • the switch assembly 50a is changed from the first configuration of Figure 6a to the second configuration of Figure 6b by translating the moveable assembly 80 upwards.
  • the beam dump 81 is then in front of sub-beam SB2 a and not in front of sub-beam SBl a .
  • Sub- beam SB l a is reflected by mirrors 85 and 84, which translate it vertically and bend its direction of travel, and is output as branch radiation beam B a .
  • FIGs 7a and 7b illustrate a further switch configuration, which comprises one pair of translating mirrors 94 and 95 and a translating beam dump 93 (which in other embodiments may be a plurality of beam dumps).
  • Beam dump 93 and mirrors 94 and 95 are part of a moveable assembly 92.
  • the switch assembly further comprises two mirrors 90 and 91 which are not part of the moveable assembly 92.
  • the mirrors 90, 91 which are not part of the moveable assembly may be referred to as static.
  • referring to the mirrors 90, 91 as static refers only to the fact that they do not move as part of the moveable assembly to transition the switch assembly between the first configuration and the second configuration. It does not exclude the possibility of other forms of movement, for example to finely adjust the position or orientation of mirrors 90, 91.
  • Providing mirrors that are not part of a moveable assembly may reduce the overall number of moving parts.
  • Sub-beam SBl a enters the switch assembly diagonally from the top left of the figures, and SB2 a enters the switch assembly diagonally from the bottom left.
  • Sub-beam SB2 a is bent by mirrors 90 and 91 to be horizontal.
  • sub-beam SB2 a is dumped into beam dump 93 after it has been bent to horizontal by mirrors 90 and 91.
  • Sub-beam SB l a enters the moveable assembly diagonally from the top left, is bent to horizontal by mirrors 94 and 95, and is output as branch radiation beam B a .
  • the switch assembly is switched from the first configuration of Figure 7a to the second configuration of Figure 7b by translating the moveable assembly 92 vertically upwards from a first position to a second position.
  • the moveable assembly 92 is translated upwards into the second position, the horizontal portion of sub-beam SB2 a is no longer blocked by the beam dump 72 (or by any part of the moveable assembly) and becomes the output branch radiation beam B a .
  • Figures 8a and 8b show a further embodiment of a switch, in which sub-beams SBl a and SB2 a are initially substantially parallel and horizontal.
  • the switch comprises one translating mirror 105 and one beam dump 104, which are part of a moveable assembly 103.
  • the switch further comprises three static mirrors 100, 101, 102.
  • Mirror 100 bends sub-beam SB l a downwards (for example, at an angle of 20°).
  • Mirrors 101 and 102 together translate sub-beam SB2 a upwards by reflecting sub-beam SB2 a first from mirror 101 then from mirror 102.
  • sub-beam SB2 a On exiting mirror 102 sub-beam SB2 a is substantially horizontal.
  • beam dump 104 blocks sub-beam SB2 a after it exits mirror 102.
  • Sub-beam SBl a is reflected from mirror 105 to be substantially horizontal.
  • Sub-beam SBl a is output as branch radiation beam B a .
  • the switch is switched from the first configuration of Figure 8a to the second configuration of Figure 9a by translating the moveable assembly 103 vertically.
  • the beam dump 104 When translated vertically into the second configuration, the beam dump 104 no longer blocks sub- beam SB2 a but does block sub-beam SB l a .
  • Sub-beam SB2 a becomes the output branch radiation beam B a .
  • the switch embodiments of Figures 7a and 7b and 8a and 8b each comprise some static components (mirrors 90, 91 ; mirrors 100,101, 102) in addition to a single moveable assembly (92, 103).
  • the static components are considered to be part of the switch assembly.
  • the static components may be considered to be outside the switch assembly, and the switch assembly may comprise only the moveable assembly 92, 103.
  • a switch assembly (which may alternatively be called a switch module) may be a component that can connect two beam splitters, where the beam splitters look mostly the same apart from mirror inversion of the beam paths to the scanner.
  • switch assembly may comprise any suitable number of moveable assemblies.
  • a switch assembly may comprise a first moveable assembly which operates to transmit or block a first sub-beam, and a second moveable assembly which operates to transmit or block the second sub-beam.
  • the first moveable assembly may comprise at least one mirror configured to change a path of the first sub-beam when the first moveable assembly is in a first configuration and/or a second configuration.
  • the second moveable assembly may comprise at least one mirror configured to change a path of the second sub-beam when the second moveable assembly is in a first configuration and/or a second configuration
  • a switch assembly may comprise a first moveable assembly comprising one or more beam dumps and a second moveable assembly comprising one or more mirrors.
  • the moveable assemblies may move in the same or different directions in order to transition from one configuration to another.
  • the moveable assemblies may have different types of motion: for example, one may be translated and another rotated.
  • Figure 9a and 9b show a further embodiment of a switch assembly.
  • sub-beams SBl a and SB2 a enter the switch in opposing directions along the same axis, sub-beam SB l a from the left of the figure and sub-beam SB2 a from the right of the figure.
  • the switch comprises static beam dumps 115, 116 and a moveable assembly 110 comprising mirrors 111, 112, 113 and 114.
  • static beam dumps means that there are fewer moving parts than would be the case if beam dumps 115, 116 were moved. In some circumstances, the use of static beam dumps may require both FELs to be turned off during the beam switching operation, to avoid multi-kilowatt beams moving around during the operation of the switch.
  • Mirrors 111, 112 are configured to bend sub-beam SB l a upwards to vertical.
  • Mirrors 113, 114 are configured to bend sub-beam SB l a upwards to vertical.
  • the moveable assembly 110 is moveable along a horizontal axis which is the same as the axis along which the sub-beams propagate.
  • Beam dumps 115 and 116 are placed above the moveable assembly and are spaced apart, with a gap between them in the horizontal direction.
  • the moveable apparatus In a first configuration shown in Figure 9a, the moveable apparatus is placed such that mirrors 113, 114 direct sub-beam SB2 a into beam dump 116 and mirrors 111, 112 direct sub-beam SBl a into the gap between beam dumps 115 and 116 (and as branch radiation beam B a towards a lithographic apparatus, not shown).
  • the moveable assembly 110 To move from the first configuration to the second configuration, the moveable assembly 110 is translated horizontally to the left, which changes the positions at which the mirrors turn the sub-beams.
  • sub-beam SB2 a is directed into the gap between the beam dumps 115 and 116 (and as branch radiation beam B a towards a lithographic apparatus, not shown) by mirrors 114, 113, and sub-beam SB l a is directed into beam dump 115.
  • Figures 10a and 10b show a further switch embodiment.
  • the switch was changed from a first configuration to a second configuration by translating at least one component of the switch, for example by translating a moveable assembly comprising at least one mirror and/or at least one beam dump.
  • the switch is changed from a first configuration to a second configuration by rotating a moveable assembly 120 around an axis of rotation 124.
  • Figure 10a shows a first configuration of the switch.
  • Sub-beams SBl a and SB2 a enter moveable assembly 120 from the top left and bottom left respectively.
  • Moveable assembly 120 comprises a beam dump 121 and two mirrors 122, 123.
  • Beam dump 121 blocks SB2 a but does not block SB l a .
  • SB l a is bent to horizontal by mirrors 122 and 123 and exits the moveable assembly 120 as branch radiation beam B a .
  • Rotational axis 124 is horizontal and passes along the path of branch radiation beam B a .
  • Rotational axis 124 passes through the beam dump at a point that is further from SB2 a than from SB l a , such that more of the beam dump is below the rotational axis 124 than is above the rotational axis 124.
  • the rotational axis 124 passes through each of the mirrors 122, 123.
  • the moveable assembly is rotated around the horizontal rotational axis 124 by 180°.
  • the beam dump 121 and mirrors 122, 123 are therefore inverted.
  • the beam dump 121 now blocks SBl a but does not block SB2 a .
  • the mirrors bend SB2 a to horizontal, and SB2 a exits the moveable assembly 120 as branch radiation beam B a , along the rotational axis.
  • Figure 10c and lOd show a similar switch embodiment to that of Figures 10a and 10b.
  • the same component numbering is used for moveable assembly 120, beam dump 121, mirrors 122 and 123, and axis of rotation 124.
  • Figures 10c and lOd include extra details of the implementation of the switch assembly.
  • a tradeoff may have to be made between (1) having the actuators inside the vacuum, so that the connection of the beam pipes to the switch unit is static, or (2) letting the switch actuation be outside the vacuum. If the switch actuation is outside the vacuum, the connection of the beam pipes to the moveable assembly may be dynamic and/or a connection to the mirror(s) and/or beam dump(s) may be dynamic.
  • the vacuum chamber used for the switch may be rather large and may contain the actuators and cables used to operate the switch. If option (2) is selected, the vacuum chamber may be smaller, but large bellows may be required to connect to the actuators and/or to the beam pipes. [00176]
  • the actuators of the mirrors which provide active control of the mirrors during operation may be inside the switch (and in vacuum).
  • actuation of the switch is performed outside the vacuum.
  • the illustration of moveable assembly 120 may be considered to represent the extent of a vacuum chamber.
  • An interface to the moving chamber is via vacuum preloaded air bearings (fixed air bearing 200).
  • the rotating unit contains the mirrors and the beam dump.
  • An actuator for rotation is not illustrated but is positioned outside the switch unit.
  • a groove 202 is for air when rotating the switch, and vacuum otherwise.
  • a further groove 204 is a vacuum groove.
  • any appropriate components may be translated and/or rotated to change the switch configuration.
  • Any components that are to be translated may be mounted on rails.
  • a plurality of components may be mounted on rails as a unit to form a switchable module.
  • a switch assembly may be provided as a single unit (for example, a unit comprising at least one beam dump and at least one mirror) which is moveable between switch positions to provide a first and second switch configuration.
  • Figures 11a to l id show a switch of another embodiment in which incoming sub- beams are parallel and a moveable assembly 130 comprises one rotating mirror 132 with a beam dump 135.
  • the moveable assembly 130 is configured to be rotated to switch between a first configuration (shown in Figures 11a and l ib) and a second configuration (shown in Figures 11c and l id).
  • Figures l ib and l id provide an end view of Figures 11a and 11c respectively.
  • the switch of Figures 11a to l id comprises static mirrors 131, 133 and 134 and a moveable assembly 130 comprising a mirror 132 and a beam dump 135 that is L-shaped in cross-section when viewed along the direction of arrival of the sub-beams (see Figures l ib and l id).
  • Sub-beams SB l a and SB2 a are parallel and horizontal on arrival. Sub-beam SBl a is bent downwards by mirror 131. Sub-beam SB2 a is translated vertically by mirrors 133 and 134. In the first configuration ( Figures 11a and l ib), sub-beam SB2 a is blocked by beam dump 135 and sub-beam SBl a enters the moveable assembly 130 and is reflected by mirror 132 to exit the moveable assembly horizontally as branch radiation beam B a .
  • Figure l ib represents the switch as viewed from the right end of Figure 11a.
  • Sub- beam SBl a passes over the top leg of beam dump 135 and reflects from mirror 132 then exits the moveable assembly 130 in a direction coming out of the page.
  • Sub-beam SB2 a reflects from mirror 133 and mirror 134 (in this view, hidden behind the top leg of beam dump 135) into the top leg of beam dump 135.
  • the moveable assembly is rotated clockwise by 90° as viewed in Figures l ib and l id.
  • the leg of the L- shaped beam dump that was previously to the left of Figure l ib is now at the top of Figure l id. Since it comes higher than the leg that was previously at the top, it blocks SB l a after SBl a is reflected from mirror 131. Since it does not extend as far down as the leg that was previously at the top, it no longer blocks SB2 a after SB2 a is reflected from mirror 134.
  • SB2 a now exits the moveable assembly 130 horizontally (as branch radiation beam B a ) as viewed in Figure 11c (out of the page, as viewed in Figure l id).
  • Mirror 132 is rotated with the moveable assembly so that it is out of the path of both SBl a and SB2 a .
  • Figures 12a and 12b show a further embodiment of a switch in which a moveable assembly 140 is translated between a first position (a first switch configuration) and a second position (a second switch configuration).
  • Moveable assembly 140 comprises two beam dumps and two mirrors.
  • first sub-beam SBl a is reflected from mirror 142 and then bent upwards by bender 51a towards a lithographic apparatus.
  • Second sub-beam SB2 a is dumped into beam dump 143.
  • second sub-beam SB2 a is reflected from mirror 144 and then bent upwards by bender 51a.
  • First sub-beam SB l a is dumped into beam dump 141.
  • Figures 13a and 13b show a further embodiment of a switch in which a moveable assembly 150 is translated between a first position and a second position.
  • Moveable assembly 150 comprises mirrors 151 , 153 and a beam dump 152.
  • first sub-beam SBl a is reflected from mirror 151 and then bent upwards by bender 51a towards a lithographic apparatus.
  • Second sub-beam SB2 a is dumped into beam dump 152.
  • Figure 12b second sub-beam SB2 a is reflected from mirror 153 and then bent upwards by bender 51a.
  • First sub-beam SB l a is dumped into beam dump 152.
  • each mirror may be replaced by multiple mirrors.
  • each mirror may have a lower angle of incidence and may experience less heating.
  • each chain of splitters (the chain splitting RBI and the chain splitting RB2) may be arranged approximately in a straight line, such that the arrangement of the two chains of splitters forms an elongated V.
  • the switches 50 may be positioned between the legs of the V.
  • the switch embodiments of Figure 5, 7, 10, 12 and 13 may be preferred in some embodiments of the system.
  • the embodiment of Figure 5 is similar to that of Figure 13, but with more mirrors.
  • the embodiments of Figures 12 and 13 are similar, but for different angles of incoming sub-beam. Any of the switch embodiments shown (or other embodiments) may be present in one total system.
  • the embodiment of Figure 10 differs from other embodiments illustrated in that it is moved by rotation rather than by translation.
  • beam paths may be three-dimensional.
  • beams or sub-beams may be translated or bent both laterally and vertically.
  • a splitter may split off multiple sub-beams having different horizontal trajectories.
  • a splitter may split off multiple sub-beams having different vertical trajectories.
  • the sub-beams are reflected from mirrors of the switch without substantially changing the properties of the sub-beams, for example the cross-section of the sub-beams.
  • mirrors of the switch may have beam shaping properties.
  • the switch may incorporate a part of a beam shaping assembly.
  • One or more mirrors of the switch may have optical power.
  • one or more mirrors may be configured to expand a cross-section of a sub-beam. Any of the embodiments above may comprise one or more shaping mirrors.
  • Each of the switches illustrated in Figures 4a to 13b selects between two sub-beams, having a first configuration in which the first sub-beam is transmitted and a second configuration in which the second sub-beam is transmitted.
  • more than two radiation sources may be provided.
  • each switch may select between more than two sub-beams. All of the embodiments described above are extendable to more than two FELs.
  • a plurality of mirrors are mounted on a common frame (a common moveable assembly) that moves as a whole.
  • mirrors may be moved individually.
  • beam dumps may be moved individually.
  • beams from two FELs are each divided into a respective plurality of sub-beams, and switches are used to select sub-beams from the first FEL or from the second FEL for transmission to lithographic apparatuses.
  • Each lithographic apparatus comprises a respective scanner.
  • N may denote a number of scanners that may be fed by the output of a single FEL.
  • a splitter module may be used to split the beam from the single FEL into N sub-beams.
  • N may be undesirable in terms of system availability. For example, if the FEL is down for maintenance, it may be the case that all N scanners attached to the FEL will be nonproductive as well. Any downtime in the FEL may result in downtime for all N scanners.
  • Various approaches may be used to introduce redundancy. Various systems may introduce redundancy by using more than one FEL.
  • a fab comprises two independent FEL-driven litho systems. If one FEL is down, the other FEL may continue to be used. Therefore half the scanners may still be in operation if one FEL goes down.
  • Configuration 0 is illustrated in Figure 14.
  • Figure 14 represents a configuration of FELs, splitter modules and scanners. For simplicity, some system components are omitted from Figure 14. For example, Figure 14 does not show gamma mirrors, beam shapers, benders and attenuators.
  • FELl drives N scanners
  • a beam from FELl is split by a first splitter module SMI into four sub-beams driving scanners SI , S2, S3 and S4.
  • a beam from FEL2 is split by a second splitter module SM2 into four sub-beams driving scanners S5, S6, S7 and S8.
  • more than two FELs may be used, with each FEL driving N scanners.
  • Figure 15 shows a further configuration, configuration 1.
  • configuration 1 may reduce throughput loss when compared with configuration 0.
  • a switch-splitter SS connects two FELs FELl, FEL2 to 2N scanners (SI , S2 ... S8).
  • a beam from FELl and a beam from FEL2 enter the switch-splitter SS.
  • the switch-splitter has two outputs, one of which is connected to a first splitter module SMI and the other of which is connected to a second splitter module SM2.
  • SMI splits the beam from the first output into four sub-beams, driving scanners SI to S4.
  • SM2 splits the beam from the second output into another four sub-beams, driving scanners S5 to S8.
  • the switch-splitter can be interpreted as a 3-state switch.
  • the three possible states of the switch-splitter are designated SS-A, SS-B and SS-C and are shown schematically in Figure 16.
  • Each state is represented by a diagram in which two dots 200, 201 on the left side of the diagram represent input from FELl (upper dot 200) and FEL2 (lower dot 201).
  • Two dots 202, 203 on the right side of the diagram represent a first output path (upper dot 202) to first splitter module SMI, and a second output path (lower dot 203) to second splitter module SM2.
  • the beam from FELl passes into first splitter module SMI via the first output path.
  • the path of the beam from FL1 is represented by a line between the two upper dots 200 and 202.
  • the beam from FEL2 passes into second splitter module SM2 via the second output path.
  • the path of the beam from FEL2 is represented by a line between the two lower dots 201 and 203.
  • the two EUV beams may be described as being in a straight-through configuration.
  • the beams from FELl and FEL2 follow the same or similar path as a path they may have followed if switch-splitter SS were not present.
  • each beam may undergo some reflections from mirrors.
  • the switch-splitter may comprise mirrors which reflect the beams as they are passing through the switch-splitter.
  • a beam splitter (represented by dot 204) is placed into the EUV beam from FELl, thereby distributing the EUV power from FELl to both of the two attached splitter modules SMI, SM2 and thereby to all of the 2N scanners.
  • the SS-B state may be used when there is no FEL2 beam, for example when FEL2 is down for maintenance.
  • a beam splitter (represented by dot 205) is placed into the EUV beam from FEL2, thereby distributing the EUV power from FEL2 to both of the two attached splitter modules SMI, SM2 and thereby to all of the 2N scanners.
  • the SS-C state may be used when there is no FELl beam, for example when FELl is down for maintenance.
  • the throughput of the scanners may be between 50% and 100% of the original throughput.
  • the throughput of the scanners may be approximately 70% of the original throughput.
  • the throughput in state SS-B or SS-C may depend on the wafer-stage speed in the scanners (which may depend on inter-die overhead, dose requirements and/or hardware capability).
  • Figure 17 shows another configuration, configuration 2, which is similar to the configuration shown in Figure 1 (with some components omitted for clarity).
  • Two FELs FELl , FEL2 serve N scanners.
  • N 4.
  • Any suitable number of FELs may serve any suitable number of scanners.
  • a beam from FELl enters a first splitter module SMI which splits the beam into a plurality of sub-beams.
  • a beam from FEL 2 enters a second splitter module SM2 which splits the beam from FEL2 into a further plurality of sub-beams.
  • Four 2-state switches SWl , SW2, SW3, SW4 each have as their input a respective first sub- beam from FELl and a respective second sub-beam from FEL2.
  • Each switch SWl, SW2, SW3, SW4 is configured to provide power to a respective scanner SI , S2, S3, S4.
  • Each switch may supply power from either FELl or FEL2.
  • the 2-state switches SWl, SW2, SW3, SW4 are relatively simply mirror constructions, without beam splitters. Each switch can be switched between two states.
  • the two states of switch SWl designated SW1-A and SW1-B, are shown in Figure 18.
  • Two dots 210, 211 represent inputs from FELl and FEL2 respectively, and dot 212 represents the output of the switch SWl.
  • Switches SW2, SW3 and SW4 also each have two states corresponding to those shown in Figure 18.
  • state SW1-A switch SW1 outputs the sub-beam from FEL1 to scanner SI, which is shown in Figure 18 by a line connecting dots 210 and 212.
  • state SW1-B switch SW1 outputs the sub-beam from FEL2 to scanner SI, which is shown in Figure 18 by a line connecting dots 211 and 212.
  • the scanners SI to S4 may be driven by the other of FELl and FEL2, resulting in no loss of throughput.
  • Figure 19 represents a further embodiment, configuration 2a, in which switches SW1 , SW2, SW3 and SW4 of the system of Figure 17 are replaced by combiners COl, C02, C03, C04.
  • the configuration of Figure 19 may accommodate 2N scanners if each splitter module SM 1 , SM2 has 2N branches.
  • Figure 20 is a diagram representing a combiner COl combining a sub-beam SB1 from FELl and a sub-beam SB2 from FEL2.
  • Dot 220 represents the point at which sub-beam SB1 enters the combiner.
  • Dot 221 represents the point at which sub-beam SB2 enters the combiner.
  • the combiner combines input sub-beams SB 1 and SB2 to produce a single combined output C which exits the combiner at dot 222.
  • the combined output C drives a lithographic apparatus, which in the case of combiner COl is scanner SI .
  • Each of combiners C02, C03, C04 may also be configured as illustrated in Figure 20.
  • Configuration 0 may have a large throughput penalty if one of the FEL-litho systems breaks.
  • the throughput when one FEL or splitter module is out of order may be 50% less than the throughput with two working FELs.
  • Configuration 1 may also have a reduced throughput while one FEL is down.
  • One possible implementation of configuration 1 uses a grating for beam splitting in the switch-splitter SS.
  • the switch-splitter SS comprises a diffraction grating.
  • the modules also use gratings to divide beams from the switch-splitter SS into sub-beams.
  • the l st -order diffraction beam from the diffraction grating in the switch-splitter SS is therefore incident on another grating splitter.
  • Such a chain may have undesirable wavelength-power coupling.
  • the beam pointing of the first-order diffraction from the grating in the switch-splitter will depend on the wavelength from the FEL. Because both the switch- splitter SS and the splitter modules SMI , SM2 use gratings, tiny beam-pointing fluctuations may turn into dose fluctuations in the branches going to the scanners.
  • the switch- splitter SS of configuration 1 may comprise moving components in vacuum. Providing moving components in vacuum may be mechanically different.
  • the switch-splitter device SS may act as a single point of failure. If the switch-splitter device SS breaks or needs to undergo maintenance, it may put all 2N scanners out of order. If one of the splitter modules SMI , SM2 breaks, N out of 2N scanners may be put out of order. Even if two FELs are attached to a double PBT (Photon Beam Transport) comprising 2N scanners with some kind of switching/splitting mechanism, a problem in the PBT switching mechanism may lead to all attached scanners going down.
  • PBT Photon Beam Transport
  • Configuration 2 does not have the switch-splitter assembly as a single point of failure, or the combination of gratings found in configuration 1 , although it does have moving parts in vacuum. However, configuration 2 may have greater capital costs per kW of usable EUV source power when compared with configuration 1. For example, there may be a doubling of FEL-related capital costs per scanner.
  • the switching mechanism is moved to the scanners. There is no single point of failure that may bring down all N litho scanners. The scanners may continue to operate at 100% throughput even when one FEL or splitter module is down.
  • configuration 2a is implemented using facet mirrors (which may be interleaved mirrors which may be referred to as window blinds). Facet mirrors may be expensive to manufacture or difficult to align. It may be difficult to balance diffraction effects which may need to be big enough to fill up holes between slices and small enough to prevent other issues.
  • a grating-based attenuator downstream may be impacted by a spread in wave vectors introduced by diffraction from window blind facet mirrors.
  • Edge- diffraction effects may be experienced in configuration 2a that may not be experiences in configurations 0, 1 or 2.
  • configuration 3 the litho system is arranged as shown in Figure 21 , with 2N scanners. Each pair of scanners is connected via switch-splitters SS11 , SS12, SS13, SS14.
  • each switch-splitter SS11 , SS12, SS13, SS14 is similar to the one described above with relation to configuration 1 ( Figures 15 and 16).
  • Each switch- splitter uses moveable mirrors and a grating to take one of three possible states (SS11-A, SS11-B, SS11-C). In other embodiments, window blinds facet mirrors may be used.
  • a beam from FEL1 enters a first splitter module SMI which splits the beam from FEL1 into a first plurality of sub-beams.
  • a beam from FEL 2 enters a second splitter module SM2 which splits the beam from FEL2 into a second plurality of sub-beams.
  • a plurality of 3-state switch-splitters SS11 , SS12, SS13, SS14 each receive a respective first sub-beam from splitter module SMI and a respective second sub-beam from SM2 and output beams to a respective pair of scanners.
  • switch- splitter SS11 receives a first sub-beam from splitter SMI and a second sub-beam from splitter SM2.
  • Switch-splitter SS11 is configured to output beams to scanner SI and scanner S5.
  • Figure 22 shows the three states SS 11 - A, SS 11 -B , SS 11 -C of 3-state switch-splitter SS11.
  • Dots 230, 231 represent the input from SMI (dot 230) and SM2 (dot 231).
  • Dots 232, 233 represent output to scanner SI (dot 232) and S5 (dot 233).
  • the sub-beam from SMI is passed through to scanner SI and the sub-beam from SM2 is passed through to scanner S5, as shown by a line connecting dot 230 to dot 232 and a line connecting dot 231 to dot 233.
  • the sub-beam from SMI is split between scanner SI and scanner S5.
  • Additional dot 234 represents a beamsplitter placed in a line between dot 230 and dot 232, and a line connects dot 234 to dot 233 (representing the output to S5). No sub-beam from SM2 is present.
  • the sub-beam from SM2 is split between scanner SI and scanner S5, and no sub-beam from SMI is present.
  • Additional dot 235 represents a beamsplitter placed in a line between dot 231 and dot 233, and a line connects dot 235 to dot 232 (representing the output to SI).
  • Figure 23 shows a further configuration, configuration 4, which is similar to configuration 3, but each switch-splitter SS11 , SS 12, SS13, SS14 is implemented as a mixer.
  • Figure 24 is a schematic diagram of a mixer Ml.
  • Input II is an input sub-beam from FELL
  • Input 12 is an input sub-beam from FEL2.
  • Power from input II is distributed over outputs 01 and 02. A first part of input sub-beam II is transmitted to output 01 and a second part of input sub-beam II is transmitted to 02.
  • power from input 12 is distributed over outputs 01 and 02.
  • a first part of input sub-beam II is transmitted to output 01 and a second part of input sub-beam II is transmitted to output 02.
  • the output from 01 of mixer Ml is used to drive a first lithographic apparatus, scanner SI.
  • the output from 02 of mixer Ml is used to drive a second lithographic apparatus, scanner S5.
  • Each scanner is therefore driven by radiation from both FELs in normal use.
  • the attached scanners will receive half of the nominal power.
  • the attached scanners receive half nominal power without any change being made to the configuration of the mixer, for example without moving any part of the mixer.
  • the mixers may be implemented with gratings or facet mirrors, or with rotating mirrors (which may be moving window-blind mirrors). In some embodiments of configuration 4, there may be no moving parts in vacuum.
  • Figure 25 illustrates an implementation of a mixer with a grating.
  • Figure 25 is illustrated as a top view.
  • Inputs II and 12 (comprising a first sub-beam from FELl and a second sub-beam from FEL2) are incident upon a diffraction grating G.
  • the diffraction grating G is designed such that input II only has diffraction orders -1, 0 and input 12 only has diffraction orders 0, +1.
  • the grating G is at grazing incidence, having grazing angles below 5°.
  • Each of outputs 01, 02 comprises radiation from both the first sub-beam and the second sub-beam.
  • Figures 26 and 27 illustrate a facet-mirror-based mixer.
  • Figure 26 shows a single facet mirror with one input beam IN and two output beams OUT1, OUT2.
  • Figure 27 shows how four facet mirrors FM1 , FM2, FM3, FM4 and a few regular mirrors Ml , M2 may be used to mix inputs II, 12 to outputs 01, 02.
  • a radiation beam from input II is split into a first sub-beam and a second sub-beam by facet mirror FM1.
  • the first sub-beam is incident on facet mirror FM3 and contributes to output 01.
  • the second sub-beam is incident on facet mirror FM4 and contributes to output 02.
  • a radiation beam from input 12 is split into a first sub-beam and a second sub-beam by facet mirror FM3.
  • the first sub-beam is reflected by mirrors Ml and M2 such that it is incident on facet mirror FM3 and contributed to output 01.
  • the second sub-beam is incident on facet mirror FM4.
  • a greater number of regular mirrors may be used.
  • litho scanners are grouped in pairs, each pair being fed by the EUV output of two FELs through a mixer.
  • Each mixer has two inputs and two outputs; each output receives half the power of each input. If one of the inputs is down, then both attached litho scanners will still receive half of their original input power.
  • Figures 21 and 22 may each provide a redundant FEL layout, in which each litho scanner receives light from each of the two FELs, such that each litho scanner can continue to operate even if one FEL is not operating.
  • Two-way mixer gratings may have a sensitivity of output split ratio versus input angle. Since the input of these mixer gratings is the output of a splitter grating, there may be a wavelength stability condition for the FEL of ⁇ / ⁇ > 10 ⁇ 3 . Increased sensitivities to thermal deformations in the splitter gratings and in the optics between the FEL undulator and the first splitter grating may be expected. Going from the baseline (N litho scanners) to the redundant layout with 2N scanners, the aberrations due to thermal distortions of the gratings may increase roughly by a factor of 8.
  • Figure 28 shows an arrangement of a diffraction grating as a mixer.
  • Input beams 250, 260 are incident on diffraction grating 270.
  • diffraction grating 270 is designed such that input beam 250 only has diffraction orders - 1, 0 and input beam 260 only has diffraction orders 0, +1.
  • Figure 28 shows a footprint 252 of input beam 250 on the grating 270, and a footprint 262 of input beam 260 on the grating 270.
  • the input beams' vectors and the grating line pitch of the grating 270 are arranged such that each beam has only one nonzero diffraction order, with the diffracted beam vector overlapping with the specularly reflected beam vector from the other input beam.
  • the specularly reflected beam 254 from input beam 250 overlaps the diffracted beam 266 from input beam 260.
  • the specularly reflected beam 264 from input beam 260 overlaps the diffracted beam 256 from input beam 250.
  • the cross-sectional shape of each diffracted beam is different from the cross-sectional shape of its corresponding input beam. With two circular input beams, the diffracted outputs have elliptical cross section.
  • each scanner will receive a superposition of two beams that may be considered to have a strange cross section.
  • the cross section may be difficult to deal with in a subsequent beam path to an illuminator.
  • An existing concept of the subsequent diffusing and focusing optics used in the beam path may require a smooth intensity profile of the beam in order to eliminate or reduce sensitivity to beam-pointing fluctuations.
  • a beam output from the mixer is intended to end up on a diffuser, for example a faceted diffuser.
  • the faceted diffuser may comprise, for example, a diffuser as described in International Patent Application WO2016/139055. Both the specular beam (having a round cross-section) and the diffused beam (having an elliptical cross- section) may have to cover a sufficient number of diffusing facets.
  • a beam cross section on exiting the mixer may correspond to a spot shape on pupil facet mirrors in an illuminator of a litho scanner. The litho scanner may be calibrated and optimized for a particular spot shape.
  • the cross section will change, which may have consequences for the scanner performance. If one FEL stops operating, the illuminator may need to be re-optimized. If one input (from one FEL) goes dark, a new scanner optimization may be required, which may impact the productivity of said litho scanner.
  • Figure 29 illustrates an implementation of a mixer that may avoid the issue of non- overlapping beam spots.
  • Non-circular input-beam cross-sections are used.
  • By using non- circular input-beam cross-sections it may be possible to obtain output cross-sections such that an output cross-section of a diffracted beam from one input substantially overlaps the output cross-section of the specular beam from the other input.
  • the output beams from the splitter modules are shaped such that they have an overlapping, symmetrical, elliptical footprint on the mixer grating. This layout may be embedded into an entire FEL/fab system.
  • Two input beams 280, 282 are incident on a grating 284.
  • the beam footprints on the grating 284 are the same for both input beams 280, 282.
  • the common beam footprint is shown as footprint 286 in Figure 29.
  • the common beam footprint 286 is an ellipse aligned with the long axis of the grating. Given the footprint and the grazing angle of incidence, the shapes of the input and output beam cross section may be determined.
  • Figure 29 shows a common output cross section 288 of the diffracted beam from input 280 and the specular beam from input 282; and a common output cross section 290 of the diffracted beam from input 282 and the specular beam from input 280.
  • the angle of incidence and the angle between two input beams may be chosen as described below with reference to Figure 30.
  • Diffraction from a grating with the grooves not perpendicular to the incident beam vector is called conical diffraction.
  • the vectors of all diffraction orders will be on a conical surface.
  • Figure 30 shows a symmetry plane 300, a first input 301 at an angle a to the left of symmetry plane 300, and a second input 302 at angle a to the right of symmetry plane 300.
  • a beam that has a cross-section that is as close to circular as possible It may be considered desirable that the beam exiting the grating be as close to circular as possible.
  • a small angle a may be used, where a is the angle as shown in Figure 30.
  • Beam handling before and after the mixer grating 284 may be considered.
  • At least two mirrors with optical power may be used to create an elliptical cross section.
  • Beams entering the mixer grating originate from as diffracted beams from diffraction gratings in the PBT splitter system. Those diffracted beams will likely also have an elliptical cross-section, but the ellipse may have a different aspect ratio and orientation from an aspect ratio and orientation that is selected for the beams entering the mixer grating.
  • a beam path may be set up as in Figure 31.
  • Figure 31 shows a beam path up to a mixer grating M.
  • a radiation beam RBI originates from FEL1 (not shown, but positioned to the left of the beam path shown in Figure 31 such that RBI originates from FEL 1).
  • the radiation beam RB I enters a first grating splitter Gl , which is part of splitter module SMI.
  • the remaining part of radiation beam SB1 proceeds to a second grating splitter G2 which is also part of splitter module SMI.
  • the radiation beam When the radiation beam enters Gl, the radiation beam may have a circular cross section (represented by box 310) or an elliptical cross section (represented by box 312).
  • sub-beam SBla On exiting Gl , sub-beam SBla has the elliptical cross section shown in box 314.
  • a pair of beam shapers Shapl, Shap2 is used to turn the elliptical output of grating Gl into an ellipse with the desired inclination angle and aspect ratio.
  • the path from the mixer to the scanner may also include other shaping optics.
  • a shaper for example, Shapl or Shap2
  • the beam path of Figure 31 comprises a first beam shaper Shapl configured to turn sub-beam SB la (which after the first grating splitter Gl has elliptical cross section 314) into circular cross section (shown in box 316).
  • the beam path further comprises a second beam shaper Shap2 configured to turn the circular cross section that has been obtained using Shapl into the desired ellipse (shown in box 318).
  • the ellipse of box 318 may have different parameter values than the ellipse of box 314.
  • the ellipse of box 318 may have a different aspect ratio and/or orientation.
  • Each beam shaper Shapl, Shap2 may comprise a set of curved mirrors configured to change the cross-sectional shape of the beam.
  • sub-beam SB la On exiting Shap2, sub-beam SB la (now having the desired elliptical cross section) enters mixer M. A further sub-beam SB2a from FEL2 also enters mixer M2. Sub-beam SB2a may have been shaped by a further first beam shaper and further second beam shaper (not shown). Sub-beam SB2a has an elliptical cross section shown in box 320. The elliptical cross-section of sub-beam SB2a has a different orientation to that of sub-beam SBla. Sub- beam SB2a may have been shaped by a further first beam shaper and further second beam shaper (not shown in Figure 31).
  • Mixer M mixes sub-beams SB la and SB lb such that each of the outputs 01, 02 of mixer M comprises a part of sub-beam SB la and a part of sub-beam SB lb.
  • 01 and 02 have cross sections as shown in boxes 322 and 324 respectively.
  • Output 01 drives a first scanner (for example, SI) and output 02 drives a second scanner (for example, S5).
  • sub-beams SB la and SB2a By shaping sub-beams SB la and SB2a to have an elliptical cross-section on entering the mixer, parts of the output beams from the mixer may be better superimposed than if the sub-beams SB la and SB2a were circular on entering the mixer.
  • a cross-section of the diffracted part of SB la may resemble a cross-section of the specular part of SB la, and vice versa.
  • functions of Shapl and Shap2 may be combined in a single beam shaper.
  • the functions of Shap 1 and Shap2 (with an intermediate, circular beam cross section) may be merged into a single shaper without an intermediate circular beam cross section.
  • one may not be free to choose the orientation of the output ellipse that is output from the single beam shaper.
  • Additional mirrors may be used to rotate the ellipse that is output from the single beam shaper into the desired orientation.
  • the additional mirrors may be flat mirrors. In some circumstances, flat mirrors may be more cost-effective. For example a single beam shaper plus additional flat mirrors may be cheaper than two beam shapers.
  • ten litho scanners are fed by a single FEL with five 3-way grating beam splitters.
  • a cumulative effect of thermal deformation may present issues in this layout.
  • a cumulative effect of thermal deformations may be worse if the length of the beam path from the first to the last splitting grating is larger. Therefore, for example, a single FEL feeding ten litho scanners may result in more thermal deformations than if a single FEL were to feed five litho scanners.
  • the impact of a deformed grating may scale roughly as PL 2 for an incident power P and a distance to the last grating L, where L is proportional to the number of attached scanners.
  • L may double. For example, instead of two FELs each feeding five scanners as in configuration 0, one may have two FELs each feeding all ten scanners, with each scanner receiving radiation from both FELs.
  • the number of gratings with a significant thermal deformation may double as well. This may result in an eight-fold increase in the impact of thermal deformations of the splitter gratings. In a decision of whether or not to implement the present redundancy concept of configuration 4, an extra cost and risk of handling thermal deformations may be considered.
  • the elliptical beam is turned back into a beam with a circular cross-section. In other embodiments, the elliptical beam is not turned back into a beam with a circular cross-section.
  • the beam exiting the mixer may pass through further components. For example, in some embodiments, the beam exiting the mixer passes into a faceted diffuser.
  • a faceted diffuser is designed to accept an elliptical beam cross section, as long as the major and minor axes of the ellipse are aligned with the s and p directions (where s and p directions are, respectively, perpendicular and parallel to a plane of incidence).
  • the system may be designed to get all the beam cross sections to arrive with the desired orientation at the focusing optics for each litho scanner.
  • All beam paths may be laid out such that the different scanners will receive the same polarizations. All beam paths may be laid out in 3D space with all beam cross sections at the desired orientations.
  • a PBT layout with mixers is implemented without combining functions, for example by separating polarization control from beam cross-section control.
  • Embodiments in which functions are not separated may in some circumstances use extra mirrors when compared with embodiments in which functions are combined.
  • separation of functions for example, separation of polarization control and beam cross- section control
  • Grating design and wavelength sensitivity may be considered. It may be possible to design a splitting grating (for example, the grating shown in Figure 29) such that the split ratio has a low sensitivity to the wavelength of the input. However, it may be difficult to ensure that beam pointing fluctuations of the input have a low impact on the sensitivity. Because the inputs to the mixer 284 of Figure 29 are the outputs of the splitter module (for example, splitter module SMI of Figure 23) and said splitter module uses gratings to split off beams, a wavelength shift of either FELl or FEL2 may result in a beam pointing shift in the output of the respective splitter module.
  • the splitter module for example, splitter module SMI of Figure 23
  • the output of a 2-way split grating may be characterized by the reflectances R 0 and ff ⁇ 1 , where R 0 is the fraction of input power that goes into the specular beam and R ⁇ 1 is the fraction of input power that goes into the diffracted output beam.
  • Reflectances R 0 and R ⁇ 1 may be sensitive to input parameters comprising wavelength ⁇ , grazing angle ⁇ , and azimuthal angle ⁇ . Additionally, the beam pointing of the diffracted output may be sensitive to the input wavelength.
  • the sensitivities of R 0 to ⁇ , ⁇ and ⁇ may be close to zero. If these conditions are satisfied for R 0 , the sensitivities of R ⁇ 1 may also be close to zero.
  • a shape of grating grooves of the grating may affect the sensitivities.
  • groove pitch there are three main groove parameters than can be chosen: groove pitch, groove width and groove depth.
  • a possible fourth parameter may be groove sidewall slope. However, in some circumstances there may be little freedom in manufacturing for groove sidewall slope.
  • the first parameter, groove pitch may already be fixed by the input beam vectors. Hence, two parameters (groove width and depth) may be available to optimize for the two independent sensitivity requirements.
  • One source of input beam-angle variation may be wavelength fluctuation of the FEL output combined with its effect on beam pointing at the splitter gratings (Gl, G2 of Figure 31).
  • Splitter gratings may be arranged as in Figure 32.
  • a wavelength-beam-pointing coupling may be expressed as
  • a small beam diameter may be used on the splitter grating (for example, grating Gl of Figure 31), followed by a beam expander (beam shaper) towards a larger beam diameter at the mixer grating (for example, mixer M of Figure 31).
  • the beam expander may reduce angular errors.
  • the mixer grating may be optimized such that the beam- pointing sensitivity is small for at least one specific linear combination of azimuth and grazing angle deviations.
  • the beam path may be set up such that wavelength variations propagate along the less sensitive axis.
  • a switch assembly may comprise any suitable number of beam dumps and/or mirrors.
  • a switch assembly may also comprise other elements.
  • a switch assembly may comprise any appropriate type of sensor, for example sensors for beam position measurement.
  • Lithographic system LS may comprise any number of lithographic apparatuses.
  • the number of lithographic apparatuses which form a lithographic system LS may, for example, depend on the amount of radiation which is output from a radiation source 30, 40 and on the amount of radiation which is lost in beam delivery.
  • the number of lithographic apparatuses which form a lithographic system LS may additionally or alternatively depend on the layout of a lithographic system LS and/or the layout of a plurality of lithographic systems LS.
  • Embodiments of a lithographic system LS may also include one or more mask inspection apparatus MIA and/or one or more Aerial Inspection Measurement Systems (AIMS).
  • the lithographic system LS may comprise a plurality of mask inspection apparatuses to allow for some redundancy. This may allow one mask inspection apparatus to be used when another mask inspection apparatus is being repaired or undergoing maintenance. Thus, one mask inspection apparatus is always available for use.
  • a mask inspection apparatus may use a lower power radiation beam than a lithographic apparatus. Further, it will be appreciated that radiation generated using a free electron laser FEL of the type described herein may be used for applications other than lithography or lithography related applications.
  • grazing incidence angle refers to the angle between the propagation direction of an incident radiation beam and a reflective surface that it is incident upon. This angle is complementary to the angle of incidence, i.e. the sum of the grazing incidence angle and the angle of incidence is a right angle.
  • the term "relativistic electrons” should be interpreted to mean electrons which have relativistic energies.
  • An electron may be considered to have a relativistic energy when its kinetic energy is comparable to or greater than its rest mass energy (511 keV in natural units).
  • a particle accelerator which forms part of a free electron laser may accelerate electrons to energies which are much greater than its rest mass energy.
  • a particle accelerator may accelerate electrons to energies of >10 MeV, >100 MeV, >1 GeV or more.
  • Embodiments of the invention have been described in the context of a free electron laser FEL which outputs an EUV radiation beam.
  • a free electron laser FEL may be configured to output radiation having any wavelength.
  • Some embodiments of the invention may therefore comprise a free electron laser which outputs a radiation beam which is not an EUV radiation beam.
  • EUV radiation may be considered to encompass electromagnetic radiation having a wavelength within the range of 4-20 nm, for example within the range of 13-14 nm. EUV radiation may have a wavelength of less than 10 nm, for example within the range of 4-10 nm such as 6.7 nm or 6.8 nm.
  • the lithographic apparatuses LA a to LA n may be used in the manufacture of ICs.
  • the lithographic apparatuses LA a to LA n described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.

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Abstract

L'invention concerne un système qui comprend une première source de rayonnement conçue pour fournir un premier faisceau de rayonnement, au moins un séparateur conçu pour diviser le premier faisceau de rayonnement en une première pluralité de sous-faisceaux, une deuxième source de rayonnement conçue pour fournir un deuxième faisceau de rayonnement, au moins un autre séparateur conçu pour diviser le deuxième faisceau de rayonnement en une deuxième pluralité de sous-faisceaux, et un ensemble commutateur. L'ensemble commutateur est conçu pour recevoir un premier sous-faisceau de la première pluralité de sous-faisceaux ; pour recevoir un deuxième sous-faisceau de la deuxième pluralité de sous-faisceaux dans une première configuration afin de transmettre le premier sous-faisceau suivant un trajet voulu, et dans une deuxième configuration afin de transmettre le deuxième sous-faisceau suivant ledit trajet voulu.
PCT/EP2016/078482 2015-12-23 2016-11-23 Système et procédé lithographiques WO2017108311A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021007398A1 (fr) * 2019-07-09 2021-01-14 Ipg Photonics Corporation Système laser à commutateur de durée d'impulsions
RU2802454C2 (ru) * 2019-07-09 2023-08-29 Айпиджи Фотоникс Корпорэйшн Сверхбыстрая импульсная лазерная система с быстрым переключением продолжительности импульсов

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Publication number Priority date Publication date Assignee Title
US20060139609A1 (en) * 2004-12-29 2006-06-29 Asml Netherlands Bv Methods and systems for lithographic beam generation
WO2015044182A2 (fr) * 2013-09-25 2015-04-02 Asml Netherlands B.V. Appareil d'acheminement de faisceau et procédé associé
WO2016139055A2 (fr) 2015-03-02 2016-09-09 Asml Netherlands B.V. Système de rayonnement

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060139609A1 (en) * 2004-12-29 2006-06-29 Asml Netherlands Bv Methods and systems for lithographic beam generation
WO2015044182A2 (fr) * 2013-09-25 2015-04-02 Asml Netherlands B.V. Appareil d'acheminement de faisceau et procédé associé
WO2016139055A2 (fr) 2015-03-02 2016-09-09 Asml Netherlands B.V. Système de rayonnement

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021007398A1 (fr) * 2019-07-09 2021-01-14 Ipg Photonics Corporation Système laser à commutateur de durée d'impulsions
RU2802454C2 (ru) * 2019-07-09 2023-08-29 Айпиджи Фотоникс Корпорэйшн Сверхбыстрая импульсная лазерная система с быстрым переключением продолжительности импульсов

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