CN114062384B - A method and device for detecting mask defects - Google Patents

Abstract

The present invention discloses a method and device for detecting mask defects. The specific steps of the method are as follows: (1) using a mask space image measuring device, measure the two mutually perpendicular polarization states of the transverse electric wave TE and the transverse magnetic wave TM respectively, and obtain two sets of , corresponding to the complex amplitude of the mask surface under TE and TM illumination respectively; (2) the light intensity distribution on the silicon wafer is obtained through the aerial image simulation algorithm, and the mask defects are judged according to the symmetry of the light intensity distribution and the difference in line width. The present invention adopts mature interferometer technology to accurately measure the amplitude and phase generated by the defect at the pupil, and then synthesizes the image on the silicon wafer through mature aerial image simulation to quantitatively determine the impact of the defect on the lithography process without compensation.

Description

A method and device for detecting mask defects

Technical Field

The invention belongs to the field of integrated circuit manufacturing, and in particular relates to a method and a device for detecting mask defects.

Background technique

As mask manufacturing has entered the deep sub-micron line width, defects in the mask manufacturing process have an increasingly greater impact on lithography imaging. As the numerical aperture of lithography becomes larger and larger, especially when it enters 1.35 immersion lithography, the role of polarized illumination cannot be ignored. The existing far-field imaging defect detection method (called the Aerial Image Measurement System, AIMS) is difficult to reproduce the situation of large numerical aperture. In principle, the detection of mask defects and the actual exposure results of silicon wafers will produce a large difference, and can only rely on subsequent compensation. And compensation will also require calibration depending on the different lithography processes of the user's chip, the different lithography levels, and the design and structure of the lithography machine, which will take up the user's time, delay the user's product development, and increase the user's production management costs and complexity.

Summary of the invention

The purpose of the present invention is to provide a new method and device for detecting mask defects. The present invention adopts the principle of interference to measure the amplitude and phase generated by the mask defects at the pupil, and then synthesizes the image on the silicon wafer through mature silicon wafer spatial image simulation, that is, the combination of optical interference detection and optical simulation calculation is used to solve the shortcomings of the existing method. The technical solution of the present invention is specifically described as follows.

The present invention discloses a method for detecting mask defects, and the specific steps are as follows:

(1) Based on the mask aerial image measuring device, the amplitude and phase generated by the upper surface of the mask to be measured at the pupil are measured by using interference technology; wherein:

The mask space image measuring device comprises a laser, a polarizing plate, a first beam splitter plate, a second beam splitter plate, a first aperture, a second aperture, a first reflector, a second reflector, a reference surface, a magnifying objective lens and an array sensor; the first beam splitter plate and the second beam splitter plate are semi-transparent and semi-reflective plane lenses respectively, the first aperture is arranged between the first beam splitter plate and the first reflector, the second aperture is arranged between the first beam splitter plate and the second reflector, the reference surface is arranged between the first reflector and the second beam splitter plate, and the mask to be measured is arranged between the second reflector and the second beam splitter plate; when working, the plane wave emitted by the laser is converted into polarized light through the polarizing plate, The polarized light is split into two beams by the first beam splitter, one of which is a reference beam and the other is an illumination beam. The reference beam passes through the first aperture and is incident on the first reflector. After being reflected by the first reflector, it is irradiated onto the reference surface and then incident on the second beam splitter. The illumination beam passes through the second aperture and is incident on the second reflector. After being reflected by the second reflector, the parallel light formed by irradiating the test area of the test mask, it is incident on the second beam splitter. After being separated by the second beam splitter, the reference beam is combined with the light beam separated by the second beam splitter and emitted to the magnifying objective lens. The magnifying objective lens images the reference surface and the upper surface of the test mask on the array sensor.

The light intensity of the reference surface when the first aperture is opened and the second aperture is closed recorded in the array sensor test is I ₁ (x, y), and the light intensity amplitude of the reference surface is A ₁ (x, y), which is obtained by the square root of the light intensity value of each pixel of I ₁ (x, y); the light intensity of the upper surface of the mask to be tested when the first aperture is closed and the second aperture is opened recorded in the array sensor test is I ₂ (x, y), and the light intensity amplitude of the upper surface of the mask to be tested is A ₂ (x, y), which is obtained by the square root of the light intensity value of each pixel of I ₂ (x, y); the light intensity after interference between the reference surface and the upper surface of the mask to be tested when the first aperture and the second aperture are opened at the same time recorded in the array sensor test is I (x, y), then the phase distribution φ (x, y) of the upper surface of the mask to be tested is calculated by formula 1):

I(x,y)＝| _A1 (x,y)exp(-iωt)+ _A2 (x,y)exp(iφ(x,y)-iωt)| ²

=I ₁ (x, y) + I ₂ (x, y) + 2A ¹ (x, y) A ₂ (x, y) cos (φ (x, y)) 1)

The two mutually perpendicular polarization states of transverse electric wave TE and transverse magnetic wave TM are measured respectively by using the mask space image measuring device to obtain two different sets of [A ₂ (x,y),φ(x,y)], which correspond to the complex amplitude of the upper surface of the mask to be measured under TE and TM illumination respectively;

(2) Based on the complex amplitude of the upper surface of the mask to be tested under corresponding TE and TM illumination, the light intensity distribution on the silicon wafer is obtained through the spatial image simulation algorithm, and the mask defects are judged according to the symmetry of the light intensity distribution and the difference in line width.

In the present invention, in step (1), the reflectivity of the first beam splitter plate and the second beam splitter plate is 50%.

In the present invention, in step (1), the reference beam is a transmitted beam, and the illumination beam is a reflected beam.

In the present invention, in step (1), the reference beam is a reflected beam and the illumination beam is a transmitted beam.

The present invention also discloses a device for the above detection method, which is a mask space image measuring device, which includes a laser, a polarizer, a first beam splitter plate, a second beam splitter plate, a first diaphragm, a second diaphragm, a first reflector, a second reflector, a reference surface, a magnifying objective lens and an array sensor; the first beam splitter plate and the second beam splitter plate are semi-transparent and semi-reflective plane lenses respectively, the first diaphragm is arranged between the first beam splitter plate and the first reflector, the second diaphragm is arranged between the first beam splitter plate and the second reflector, the reference surface is arranged between the first reflector and the second beam splitter plate, and the mask to be measured is arranged between the second reflector and the second beam splitter plate; when working, the plane image emitted by the laser The wave becomes polarized light after passing through the polarizer, and the polarized light is divided into two beams by the first beam splitter, one of which is the reference beam and the other is the illumination beam. The reference beam passes through the first aperture and is incident on the first reflector. After being reflected by the first reflector, it is irradiated onto the reference surface and then incident on the second beam splitter. The illumination beam passes through the second aperture and is incident on the second reflector. The parallel light formed after being reflected by the second reflector irradiates the test area of the mask to be tested and then is incident on the second beam splitter. After being separated by the second beam splitter, the reference beam is combined with the light beam separated by the second beam splitter and emitted to the magnifying objective lens. The magnifying objective lens images the reference surface and the upper surface of the mask on the array sensor.

Compared with the prior art, the present invention has the following beneficial effects:

1) The present invention uses mature interferometer technology to accurately measure the amplitude and phase of defects at the pupil, and then synthesizes the image on the silicon wafer through mature aerial image simulation to quantitatively determine the impact of defects on the lithography process without compensation. 2) The aerial image simulation algorithm has been in existence for more than ten years and can include the aberration of the lithography machine lens and the photochemical reaction model of the photoresist. The difference with the actual silicon wafer exposure results can be made very small. Compared with the existing AIMS that can only perform optical imaging, this method can in principle eliminate the difference between the existing AIMS equipment and the actual silicon wafer exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the overall structure of an implementation of the present invention (side view).

FIG2 : Computer simulation verification results of the algorithm of the present invention: TE polarization.

FIG3 : Computer simulation verification results of the algorithm of the present invention: TM polarization.

FIG. 4 : Example of image simulation results on a silicon wafer using the algorithm of the present invention: no defects.

FIG5 : Computer simulation verification results of the algorithm of the present invention (with defects): TE polarization.

FIG6 : Computer simulation verification results of the algorithm of the present invention (with defects): TM polarization.

FIG. 7 : An example of the image simulation result on a silicon wafer of the algorithm of the present invention: there are square defects of 20 nm in size.

1-laser, 2-first beam splitter, 3-first aperture, 4-second aperture, 5-first reflector, 6-second reflector, 7-reference surface, 8-mask to be tested, 9-second beam splitter, 10-magnifying objective lens, 11-array sensor.

Detailed ways

FIG1 is a schematic diagram of the overall structure of an implementation of the present invention. The plane wave emitted by the laser 1 becomes polarized light after passing through the polarizer, that is, a transverse electric wave (TE wave) and a transverse magnetic wave (TM wave) perpendicular to each other. The polarized light is divided into two beams by the first beam splitter 2, one is the reference beam AC, and the other is the illumination beam AB. AC is emitted to the second beam splitter 9 through the first reflector 5 and forms a beam DO. AB is reflected by the second reflector 6 to form a parallel light BD, which illuminates a part of the mask 8 to be tested. After passing through the mask 8 to be tested, it is reflected at the second beam splitter 9 and merged with the reference beam to form DO, and emitted to the magnifying lens 10. The magnifying lens 10 images the reference surface 7 and the upper surface of the mask on the array sensor 11. Among them, the optical path E _ref D = ED, OG = 10~100*E _ref O, that is, the magnification of the magnifying lens 10 is 10~100 times, and the 140nm size image on the mask to be tested is magnified to 1.4~14μm (micrometer). This size corresponds to the pixel size of the array sensor 11. Optical path AB+BD=AC+CD.

The first beam splitter plate 2 and the second beam splitter plate 9 are semi-transparent and semi-reflective plane lenses, preferably with a reflectivity of 50%. The first aperture 3 and the second aperture 4 can independently control the on and off of the optical paths AC and AB, respectively. When the first aperture 3 is opened and the second aperture 4 is closed, the array sensor 11 records the light intensity I ₁ (x, y) of the reference surface 7. Conversely, that is, the second aperture 4 is opened and the first aperture 3 is closed, the array sensor 11 records the light intensity I ₂ (x, y) on the upper surface of the mask. When the first aperture 3 and the second aperture 4 are opened at the same time, the array sensor 11 records the light intensity I (x, y) after the interference between the reference surface 7 and the upper surface of the mask. By taking the square root of the light intensity value of each pixel of the measured light intensity I ₁ (x, y) and light intensity I ₂ (x, y), the amplitude A ₁ (x, y) and the amplitude A ₂ (x, y) can be obtained. According to formula 1)

I(x,y)＝| _A1 (x,y)exp(-iωt)+ _A2 (x,y)exp(iφ(x,y)-iωt)| ²

=I ₁ (x, y) + I ₂ (x, y) + 2A ₁ (x, y) A ₂ (x, y) cos (φ (x, y))

1)

We can then calculate φ(x,y), which is the phase distribution of the parallel light BD on the upper surface of the mask after it passes through the mask.

This work can measure the two mutually perpendicular polarization states of transverse electric (TE) and transverse magnetic (TM) waves, and obtain two different sets of [A ₂ (x,y), φ(x,y)], corresponding to the complex amplitude of the mask surface under TE and TM illumination respectively. With these two sets of parameters, we can obtain the light intensity distribution on the silicon wafer through the spatial image simulation algorithm.

Figure 2 shows the light amplitude and phase distribution of a mask (without defects) under TE illumination. The light is then interfered with by the reference beam. The phase φ(x,y) is calculated using equation (1) through the light intensities I(x,y), _I1 (x,y), _I2 (x,y) and the light amplitudes _A1 (x,y), _A2 (x,y). The phase is then compared with the initial simulated phase and the error is only on the order of ^10-15 , which is very accurate.

Figure 3 shows the light amplitude and phase distribution of a mask (without defects) under TM illumination. The light is then interfered with by the reference beam. The phase φ(x,y) is calculated using equation (1) through the light intensities I(x,y), _I1 (x,y), _I2 (x,y) and the light amplitudes _A1 (x,y), _A2 (x,y). The phase is then compared with the initial simulated phase and the error is only on the order of ^10-15 , which is very accurate.

Figure 4 calculates the aerial image profile and light intensity distribution (without defects) under certain working conditions. The aerial image simulation algorithm used can be found in [Photolithography near the diffraction limit, Tsinghua University Press, February 2020, Chapter 11, Sections 11.4 and 11.5]. It can be seen that the line width of the five pairs of line ends is 69nm±0.1nm, and the light intensity distribution of the aerial image is symmetrical when there are no defects.

Figure 5 calculates the light amplitude and phase distribution of a mask (with a 20nm square defect) under TE illumination through simulation, and then interferes with the reference beam. Using formula (1), the phase φ(x,y) is calculated through the light intensity I(x,y), _I1 (x,y), _I2 (x,y) and the light amplitude _A1 (x,y), _A2 (x,y), and compared with the initial simulated phase, it is found that the error is only on the order of ^10-15 , which is very accurate.

Figure 6 calculates the light amplitude and phase distribution of a mask (with a 20nm square defect) under TM illumination through simulation, and then interferes with the reference beam. Using formula (1), the phase φ(x,y) is calculated through the light intensity I(x,y), _I1 (x,y), _I2 (x,y) and the light amplitude _A1 (x,y), _A2 (x,y), and compared with the initial simulated phase, it is found that the error is only on the order of ^10-15 , which is very accurate.

Figure 7 calculates the spatial image profile and light intensity distribution under certain working conditions (there is a 20nm square defect). The spatial image simulation algorithm used can be found in [Photolithography near the diffraction limit, Tsinghua University Press, February 2020, Chapter 11, Sections 11.4 and 11.5]. It can be seen that the line width (tangent-2, Cut-2) at the end of the defect is 66.38nm, which is significantly smaller than the adjacent line width of about 3nm, and the spatial image light intensity distribution is asymmetric on the left and right. Users can decide whether this defect is acceptable based on the difference in line width.

Claims (5)

1. A method for detecting defects of a mask plate is characterized by comprising the following specific steps:

(1) Based on a mask space image measuring device, measuring the amplitude and the phase generated at the pupil on the upper surface of the mask to be measured by utilizing an interference technology; wherein:

The mask space image measuring device comprises a laser, a polaroid, a first beam splitting plate, a second beam splitting plate, a first diaphragm, a second diaphragm, a first reflecting mirror, a second reflecting mirror, a reference surface, a magnifying objective lens and an array sensor; the first beam splitting plate and the second beam splitting plate are respectively semi-transparent and semi-reflective plane lenses, the first diaphragm is arranged between the first beam splitting plate and the first reflecting mirror, the second diaphragm is arranged between the first beam splitting plate and the second reflecting mirror, a reference surface is arranged between the first reflecting mirror and the second beam splitting plate, and a mask to be tested is arranged between the second reflecting mirror and the second beam splitting plate; when the device works, plane waves emitted by the laser are changed into polarized light through the polarizing plate, the polarized light is divided into two beams by the first beam splitting plate, one beam is a reference beam, the other beam is an illumination beam, the reference beam is incident on the first reflecting mirror through the first diaphragm, is irradiated on the reference surface after being reflected by the first reflecting mirror and then is incident on the second beam splitting plate, the illumination beam is incident on the second reflecting mirror through the second diaphragm, is irradiated on a region to be detected of the mask plate to be detected after being reflected by the second diaphragm, is incident on the second beam splitting plate, is combined with the beam separated by the second beam splitting plate after being separated by the reference beam, and is irradiated on the amplifying objective, and the reference surface and the upper surface of the mask plate to be detected are imaged on the array sensor by the amplifying objective;

The light intensity of the reference surface when the first diaphragm is opened and the second diaphragm is closed is I ₁ (x, y), the light intensity amplitude of the reference surface is A ₁ (x, y), and the light intensity value of each pixel of I ₁ (x, y) is obtained by opening the root number; the light intensity of the upper surface of the mask to be tested is I ₂ (x, y) when the first diaphragm is closed and the second diaphragm is opened, the light intensity amplitude of the upper surface of the mask to be tested is A ₂ (x, y), and the light intensity amplitude is obtained by opening the root number of the light intensity value of each pixel of I ₂ (x, y); the light intensity after interference between the reference surface and the upper surface of the mask to be tested is I (x, y) when the first diaphragm and the second diaphragm which are tested and recorded by the array sensor are simultaneously opened, and then the phase distribution of the upper surface of the mask to be tested Calculated by formula 1):

1, a method for manufacturing the same

The mask space image measuring device is used for respectively measuring two mutually perpendicular polarization states of transverse electric wave TE and transverse magnetic wave TM to obtain two sets of different [ A ₂ (x, y),The complex amplitudes of the upper surface of the mask to be detected under TE and TM illumination are respectively corresponding to the complex amplitudes;

(2) Based on complex amplitude of the upper surface of the mask to be detected under the illumination of TE and TM, acquiring light intensity distribution on a silicon wafer through a space image simulation algorithm, and judging the defects of the mask according to the symmetrical condition of the light intensity distribution and the difference of line widths.

2. The method of claim 1, wherein in step (1), the reflectivity of the first beam splitter plate and the second beam splitter plate is 50%.

3. The method of claim 1, wherein in step (1), the reference beam is a transmitted beam and the illumination beam is a reflected beam.

4. The method of claim 1, wherein in step (1), the reference beam is a reflected beam and the illumination beam is a transmitted beam.

5. An apparatus for use in the method of claim 1, characterized in that it is a reticle aerial image measuring apparatus comprising a laser, a polarizer, a first beam splitter plate, a second beam splitter plate, a first diaphragm, a second diaphragm, a first mirror, a second mirror, a reference surface, a magnifying glass, and an array sensor; the first beam splitting plate and the second beam splitting plate are respectively semi-transparent and semi-reflective plane lenses, the first diaphragm is arranged between the first beam splitting plate and the first reflecting mirror, the second diaphragm is arranged between the first beam splitting plate and the second reflecting mirror, a reference surface is arranged between the first reflecting mirror and the second beam splitting plate, and a mask to be tested is arranged between the second reflecting mirror and the second beam splitting plate; when the device works, plane waves emitted by the laser are changed into polarized light after passing through the polarizing plate, the polarized light is divided into two beams by the first beam splitting plate, one beam is a reference beam, the other beam is an illumination beam, the reference beam is incident on the first reflecting mirror through the first diaphragm, is irradiated on the reference surface after being reflected by the first reflecting mirror and then is incident on the second beam splitting plate, the illumination beam is incident on the second reflecting mirror through the second diaphragm, is irradiated on a region to be detected of the mask plate after being reflected by the second diaphragm, is incident on the second beam splitting plate, and is combined with the beam separated by the second beam splitting plate after being separated by the reference beam and is irradiated on the amplifying objective, and the reference surface and the upper surface of the mask plate to be detected are imaged on the array sensor through the amplifying objective.