WO2006037675A1

WO2006037675A1 - Lighting system for a corpuscular radiation device, and method for lighting by means of a corpuscular beam

Info

Publication number: WO2006037675A1
Application number: PCT/EP2005/053717
Authority: WO
Inventors: Hans-Joachim Doering; Thomas Elster
Original assignee: Leica Microsystems Lithography Gmbh
Priority date: 2004-10-06
Filing date: 2005-07-29
Publication date: 2006-04-13
Also published as: TW200612456A; DE102004048892A1

Abstract

Disclosed are a lighting system for a corpuscular radiation device as well as a method for lighting by means of a corpuscular beam. A corpuscular beam emitted by a corpuscular beam source penetrates a condenser system and then impinges a planar object (34) that is mounted downstream. A multistage deflection system (11) is provided between the beam source and the planar object (34). Said deflection system (11) moves the corpuscular beam across the planar object (34), the cross-sectional area of the corpuscular beam being smaller than the area of the planar object (34).

Description

Lighting apparatus for a corpuscular beam device and method for illuminating with a corpuscular beam

The invention relates to a lighting system for a

Corpuscular beam. In particular, the invention relates to an illumination system for a corpuscular beam device with a particle beam source emitting a particle beam, a condenser with a condenser lens, a flat object downstream of the condenser system having a surface of a certain size.

Furthermore, the invention relates to a method for illumination with a particle beam.

US Patent 3,717,785 discloses an array of microlenses wherein each of the microlenses is surrounded by four electrodes. The microlens array is formed at least by a plate in which numerous openings are formed for the passage of a particle beam. The plate is illuminated by a particle beam surface, wherein only passes through the openings in the plate of the particle beam and is then further formed by the electrodes. US Pat. No. 6,333,508 discloses an illumination system for an electron beam lithography machine. The electron lithography machine has a lighting system with an independent emittance control built into the lighting system. In one embodiment, a conductive grid is used, which forms a plurality of microlenses, so that hereby a broad and flat particle beam for illuminating an object is generated.

The article by W. DeVore et. al., J. Vac. Be. Technol. B 14 (6), Nov / Dec 1996; entitled "High Emittance electron gun for projeetion lithography," discloses that the crossover must be small, and that there must be a large angular distribution to uniformly illuminate a mask, an illumination that is smaller in cross-section than the area the mask has, is not provided.

The article by S. van Kranen et. al., Microelectronic Engineering 57-58 (2001), 173-179, entitled "Measuring the increase in effective emittance after a grid lens", discloses increasing the effective emittance through the use of an array of quadrupoles.

The invention has for its object to provide a lighting system that allows a homogeneous and telecentric illumination of a large area with a particle beam, the emanating from a corpuscular optical source lighting has a low emittance and low illumination angle.

This object is achieved by a lighting system having the features of claim 1.

It is a further object of the present invention to provide a method of illuminating a corpuscular beam such that the high emittance required to illuminate a large area and the required high illumination angle are achieved by having a low emittance and a low illumination angle. This object is achieved by a method having the features of claim 13.

The use of a low emittance, low illumination angle source optical source has the distinct advantage that the aperture error and the axial color error of the illumination condenser have far less effect on the crossover (illumination) aberrations, resulting in lower aberrations in the overall body solar chromato-optic system , Furthermore, the arrangement according to the invention has the advantage that remaining effects of opening and color errors of the illumination condenser can be corrected. In addition, an averaging can be done via current density inhomogeneities of the corpuscular beam. In addition, the current density distribution should be homogenized over the surface to be illuminated of a flat object. This has the advantage that one achieves better power utilization and lower space charge errors.

The illumination system for a particle beam device comprises a particle beam source which emits a particle beam, a condenser system with a condenser lens and a flat object arranged downstream of the condenser system and having a surface of a specific size. Between the condenser lens of the condenser system and the flat object, a multi-stage deflection system is provided. The multi-stage deflection system moves the particle beam over the object, with the particle beam having a smaller cross-sectional area than the surface of the object.

It is advantageous if the multi-stage deflection system is a magnetic and field-compensated deflection system. Further, it may be advantageous if the multi-stage deflection system is a low capacity electrostatic deflection system. Likewise, it is conceivable that the multi-stage deflection system is designed as a combination of magnetic and electrostatic deflection systems. A controlled current or voltage in the deflection system moves the particle beam over the object. The movement of the corpuscular beam over the object may be rotational. Likewise, the motion of the corpuscular beam over the object may be linear.

The planar object may be an aperture plate on which the apertures are arranged in groups, and the particle beam is movable only over groups of the apertures. The corpuscular beam is in this case an electron beam.

Equally advantageous is the method for illumination with a particle beam. A corpuscular beam source is provided which emits a corpuscular beam. The corpuscular beam is homogenized with a condenser system having a condenser lens. Subsequently, the corpuscular beam is directed onto a planar object having a certain area, wherein the particle beam has a smaller cross-sectional area than the area of the object.

Finally, the corpuscular beam is guided over the surface of the object with a multi-stage deflection system.

Further advantageous embodiments of the invention can be taken from the subclaims.

In the drawing, the subject invention is shown schematically and will be described with reference to the figures below. Showing:

Fig. 1 is a schematic representation of the structure of an entire system of a particle beam device;

FIG. 2 shows a schematic representation of the illumination system for the particle beam device; FIG.

3 shows a schematic illustration of the illumination system for the particle beam device with multistage magnetic deflection system; 4a shows a representation of the illumination of a flat object by means of a moving particle beam; and

4b shows a further embodiment of the illumination of the planar object by means of a moving particle beam.

Figure 1 shows a schematic representation of the structure of an entire system of a particle beam device 2. In the following description, the Korpukularstrahlsystem 2 is described, while the particle beam system 2 is an electron beam system. However, it will be understood by one of ordinary skill in the art that this can not be construed as limiting the invention. The principle of the invention is applicable to all charged particle particle beams.

From an electron gun 30, an electron beam 31 is generated, which propagates in the direction of an electron-optical axis 32. The electrons emerging from the electron gun 30 have a source crossover 31 o. The electron gun is followed by a beam centering device 33, which aligns the electron beam 31 symmetrically about the optical axis 32. After the beam centering device, the electron beam 31 passes through a condenser system 10 which forms a parallel beam from the initially divergent electron beam 31. The beam formed by the condenser system has a diameter over which the intensity is homogeneously distributed. After the condenser system 10, a planar object 34 is provided. The planar object 34 is an aperture plate having a plurality of openings for generating a plurality of parallel beams 36. In the propagation direction of the beam 36 towards the target 6 is followed by a baffle plate 35, which has a plurality of

Beam deflection units has. After the deflection plate 35, an acceleration lens 39 follows, which increases the energy of the electrons in the electron beam 31 and then generates a first intermediate image of the crossover 31 ₁ at the location of the aperture 38. All individual crossover of the partial beams 36 occur almost at the same location, namely the aperture of the aperture stop 38. The diameter of the opening of the aperture stop 38 is chosen so that almost all the electrons of the undeflected beam bundles 36 can pass through the aperture diaphragm 38. Single rays 37, which have undergone an individual change of direction by the deflection plate 35, are stopped at the aperture stop 38, since their crossover intermediate image does not arise at the location of the aperture diaphragm opening. In the further course of the beam, at least one magnetic lens 40 now follows in order to reduce the image of the aperture plate 34 to the target 6. In the exemplary embodiment shown here, two magnetic lenses 40 are shown. The picture shows a second intermediate image of the crossover 31 ₂ . Before the undeflected beams 36 strike the target 6, which is for example a wafer, they pass through an objective lens 41. The objective lens 41 is equipped with a plurality of elements. Before and after a second crossover 31 _{2 of} the electron beam 31 two deflectors 45 and 46 are provided. The deflection devices 45 and 46 serve for deflecting and for determining the position of the electron beam 31 or the plurality of undeflected radiation beams 36 in the target. The two independently controllable deflection systems 45 and 46 are advantageously used to separately optimize slow and fast deflection operations. Fast sweeps in the frequency range MHz to GHz are required, for example, to hold the position of the reduced aperture plate 34 on the uniformly moving target 6 constant by means of sawtooth deflections for the duration of an exposure step or exposure stroke and then to jump in a very short time to the next exposure point. Since adjacent pixels are typically less than 100 nm apart, the fast deflection system 46 is preferably constructed as an electrostatic system. For the compensation of low-frequency position deviations of the target 6 from the uniform movement in the range of a few m, a slow but highly accurate magnetic deflection system 45 is preferably used. Further, stigmators 44 are provided which are preferably constructed as multi-layered magnetic coil systems to compensate for astigmatism and distortion caused in the optical column by manufacturing tolerances and adjustment errors. The objective lens 41 has an am Beam foot point of the electron beam 31 on the target 6 scanning height measuring system 42. The height measuring system 42 is used to detect unevenness of the target 6 (for example, wafers) and height variations that can cause a shift table. A detector 43 receives the particles or backscattered by the target 6

Electrons that arise near the beam impact points. This detector 43 serves to determine the position of marks on the target 6 for the purpose of covering a plurality of exposure planes or for calibrating control elements of an exposure system. Furthermore, there are three pairs of correction lenses 23, 24, 25 in the lower part of the

Corpuscular beam device 2. The correction lenses 23, 24, 25 are used for the dynamic correction of the focus, the image field size and the field rotation during the exposure of the continuously moving target 6. The correction lens system 23, 24, 25 allows the correction of errors caused by height variations of the target, and caused by variable space charges in the column area.

FIG. 2 shows the schematic structure of a lighting system for a corpuscular device. The electrons or particles emerging from the electron gun 30 or particle gun form the source crossover 31 ₀ . The source crossover 31 ₀ has a diameter of about 20 m. Between the source crossover 31 ₀ and the planar object 34, a deflection system 1 1 is provided. In the embodiment illustrated in FIG. 2, the deflection system 1 1 comprises a plurality of partial deflection systems H ₁ , 1 1 _2. Also, a condenser lens 12 is provided between the source crossover 31 ₀ and the planar object 34. In the embodiment shown here, the condenser lens 12 has a focal length B of 0.5 m. The source crossover 31 o is the same distance from the condenser lens 12 as the condenser lens 12 from the surface of the planar object 34. The deflection system 1 1 generates a dynamic emitter bell 13 to increase the effective emittance at the planar object to be illuminated. As already mentioned several times, the planar object 34 may be a mask or an aperture plate. The aperture plate is part of a multi-beam modulator, for example. The deflection system 1 1 consists of several Teilablenksystemen H ₁ , 1 1 ₂ , which are preferably magnetic and Außenfeld- compensated. It is particularly advantageous when two independent Teilablenksysteme H ₁ , and 1 1 ₂ are used (preferably in each case as orthogonal deflection coil pairs), which are introduced between the particle gun 30 and the sheet-like object 34 in the corpuscular optical beam path. The aperture plate has, for example, an area of 60 × 60 mm. With the illumination system for a particle beam device 2 proposed in FIG. 2, it is possible to realize the emittance required for illuminating a large area (typically: 2000 microrad x millimeter) and the high illumination angle (typically: 100 millirad). The use of a corpuscular beam source with low emittance and low illumination angle then requires the deflection system 1 1 disclosed in FIG. 2, so that the emittance required for the illumination of the planar object 34 is achieved. The corpuscular beam source with low emittance and low illumination angle has the decisive advantage that the

Aperture errors and the axial color error of the illumination condenser have far less effect on the crossover (illumination) aberrations and thus result in lower aberrations in the entire corpuscular optical system. Furthermore, the deflection system 1 1 allows an average of current density inhomogeneities of the corpuscular beam. In addition, the current density distribution is to be homogenized over the surface to be illuminated, which brings the advantage of better power utilization and thereby lower space charge error with it.

FIG. 3 shows an illumination system for a particle beam device with a multistage magnetic deflection system 11. The

Illumination device 2 defines an optical axis 15, in which the corpuscular beam source 30 is arranged. The condenser system 10 includes a magnetic condenser lens 50. The condenser magnetic lens 50 is composed of a plurality of gaps 51. A number of columns n> 5 is preferred. The particle beam 52 formed by the condenser lens 50 illuminates, preferably telecentrically, the planar object 34, which can be designed as a multi-aperture beam modulator or as an aperture plate. Accordingly, since the magnetic condenser lens 50 includes five gaps 51, there is the magnetic condenser lens 50 from a sequence of a plurality of partial lenses 50i, 50 ₂ , 50 ₃ , 50 ₄ , 50 ₅ . Each partial lens 50i, 50 ₂ , 50 ₃ , 50 ₄ , 50 ₅ has a separate winding with separately adjustable excitation. Although in FIG. 3 the magnetic condenser lens 12 is drawn only on one side of the optical axis 15, it is obvious to a person skilled in the art that the magnetic condenser lens 50 concentrically surrounds the optical axis 15. In addition to the magnetic condenser lens 50, the deflection system 11 is provided along the optical axis 15. The deflection system 1 1 consists of several paired magnetic coils. In the embodiment shown in Figure 3, three paired magnetic coils are provided. Each pair of magnetic coils consists of a deflection coil 60 and a compensation coil 62. The magnetic axis field profile 55 of the condenser lens 50 is also shown in FIG. The deflection system 1 1 is in this case arranged with respect to the optical axis 15 and is energized accordingly that the incident on the planar object 34 Korpuskularstrahl 52 parallel to the optical axis 15 extends.

FIG. 4a shows a schematic illustration of the illumination of the planar object 34 by means of a moving luminous surface 70. In the embodiment shown here, the luminous surface 70, which moves over the surface to be illuminated, is of circular design. In this case, the intensity distribution of the circular moving luminous surface 70 increases toward the center of the luminous surface 70. As a result of the electronic control of the current or the voltage in the deflection system 1 1, a larger illuminated area 71 on the planar object 34 can be covered or described by means of the luminous area 70. The movement of the blasting bell, which results in the projection in the luminous area 70, above the flat object 34 is preferably rotational. FIG. 4 a shows a linear movement of the luminous area 70. The linear motion of the spot 70 is a two-dimensional linear motion 72 resulting in an integral illumination profile in the form of a rectangle 73. FIG. 4b shows a further embodiment of the illumination of the flat object 34 by means of a moving luminous surface 80. The movement of the luminous surface 80 in this embodiment is a one-dimensional oscillatory movement 82. The luminous surface 80 has a convex configuration in this embodiment. By the one-dimensional linear

Oscillation 82 describes the light spot 80 on the flat object 34, a rectangle 83. The rectangle 83 represents an integral illumination profile of the planar object 34.

As shown in Figures 2 and 3, the deflection system 1 1 has at least two independent Teilablenksystemei 1 ^ and 1 1 ₂ . In this case, the virtual tilting point of these two independent Teilablenksysteme 1 1 ₁ and 1 1 _{2 is selected} by the specification of the control so that it is in the vicinity of the last real image of the virtual crossover in front of the target. The control of the Teilablenksysteme 1 1 ₁ and 1 1 ₂ can be done by means of current amplitudes or voltage amplitudes. Through the controllable ratio of the current amplitudes between the sub-deflection systems, the location of the virtual cross-over for the deflected beam can be influenced in such a way that crossover aberrations that arise during imaging in the corpuscular optical system are minimized. During an exposure step typically 1 to 10 high frequency (1 100 MHz)

Rotations of the beam performed. The movement speed of the deflected beam is controlled as a function of deflection amplitudes in such a way that a desired optimum, homogeneous illumination of the planar object 34 is produced. Consequently, the homogeneous illumination of the flat object 34 results in a corresponding homogeneous illumination of the openings provided in the planar object 34 or in the aperture plate. Due to the rotation of the beam, the overall length of the lighting system can be kept short. One achieves a jet oscillation with low emittance and then achieves a dynamic emittance increase caused by the rotation of the jet. Similarly, the crossover aberrations are largely suppressed or further corrected. Furthermore, current density inhomogeneities of the beam are spatially and temporally averaged by the rotation of the beam.

Claims

claims

1 . Illumination system for a particle beam device (2), comprising a particle beam source emitting a particle beam (31), a condenser system (10) with a condenser lens (12), a surface object (34) arranged downstream of the lens sensor system (10) and occupying one surface of a particular one Size possesses, characterized in that between the

A corpuscular beam source of the condenser system (10) and the planar object (34) a multi-stage deflection system (1 1) is provided, that the corpuscular beam (31) has a smaller cross-sectional area than the surface of the planar object (34), and that the multi-stage deflection system (1 1) the

Corpuscular beam over the flat object (34) moves.

2. Illumination system for a particle beam device, according to claim 1, characterized in that the multi-stage deflection system (1 1) is a magnetic and field-compensated Ablenksystem.

3. illumination system for a corpuscular beam device, according to claim 1, characterized in that the multi-stage deflection system (1 1) is an electrostatic deflection system.

4. illumination system for a corpuscular beam device, according to claim 1, characterized in that the multi-stage

Deflection system (1 1) is a combination of magnetic and electrostatic deflection systems.

5. Illumination system for a particle beam device according to claim 1, characterized in that the corpuscular beam emerging from the corpuscular beam source has a low emission angle.

6. Lighting system for a corpuscular beam after

Claim 5, characterized in that the emission angle of the corpuscular beam is in the range of 1 to 30 mrad.

7. Lighting system for a particle beam device according to one of claims 1 to 6, characterized in that a controlled current or a controlled voltage in

Deflection system moves the corpuscular beam over the object.

8. illumination system for a corpuscular beam device according to claim 7, characterized in that the movement of the particle beam over the object is rotational.

9. Lighting system for a corpuscular beam after

Claim 7, characterized in that the movement of the corpuscular beam over the object is linear.

10. Illumination system for a particle beam device according to claim 7, characterized in that the movement of the corpuscular beam over the object is a linear oscillating movement.

1 1. Illumination system for a corpuscular beam device according to one of claims 1 to 10, characterized in that the flat object is an aperture plate, that the apertures are arranged in groups, and that the corpuscular beam is movable only over groups of the apertures.

12. Illumination system for a particle beam device according to one of claims 1 to 1 1, characterized in that the corpuscular beam is an electron beam.

13. Method for illuminating with a corpuscular beam, characterized by the following steps:

Providing a corpuscular beam source,

Homogenizing a corpuscular beam with a condenser system having a condenser lens,

Directing the corpuscular beam onto a planar object having a certain area, the corpuscular beam having a smaller cross-sectional area than the area of the object, and

• Guiding the corpuscular beam over the surface of the object with a multi-stage deflection system.

14. The method according to claim 13, characterized in that the multi-stage deflection system is a magnetic and field-compensated Ablenksystem.

15. The method according to claim 13, characterized in that the multi-stage deflection system is an electrostatic deflection system.

16. The method according to claim 13, characterized in that the multi-stage deflection system is a combination of magnetic and electrostatic deflection system.

17. Method according to claim 13, characterized in that the corpuscular beam emerging from the corpuscular beam source is emitted with a low emission angle.

18. The method according to claim 17, characterized in that the emission angle of the corpuscular beam is in the range of 1 to 30 mrad.

19. The method according to any one of claims 13 to 18, characterized in that with a controlled current or with a controlled voltage in the deflection system of the corpuscular beam is moved over the object.

20. The method according to claim 19, characterized in that the corpuscular beam is guided over the object with a rotational movement.

21. A method according to claim 19, characterized in that the corpuscular beam is guided over the object with a linear movement.

22. The method according to claim 19, characterized in that the corpuscular beam over the object with a linear

Oscillation is performed.

23. The method according to any one of claims 13 to 22, characterized in that the object is an aperture plate, that the apertures are arranged in groups, and that the corpuscular beam is moved only over groups of the apertures.

24. The method according to any one of claims 13 to 22, characterized in that the corpuscular beam is an electron beam.