CN101236362A - On-line detection method for wave aberration of projection objective lens in lithography machine - Google Patents

Abstract

The invention relates to an online detection method for the wave aberration of the projection objective lens of a photolithography machine. By integrating the interferometer device on the lithography machine, the on-line detection, correction and control of the wave aberration of the projection objective lens are carried out. The interferometer device is a point diffraction interferometer or a slit diffraction interferometer, which has two measurement modes: PSI measurement mode and FTM measurement mode. The PSI measurement mode adopts phase-shifting interferometry, which has high measurement accuracy, and is mainly used for system error calibration of the interferometer device; the FTM measurement mode uses Fourier transform method to process interference fringes, and the measurement speed is fast, mainly in the online detection of wave aberration of the projection objective lens and controls are used. This method improves the measurement accuracy without reducing the detection speed; and under the premise of not reducing the contrast of the interference fringes, the system error caused by each component of the interferometer device is calibrated by using a higher-quality spherical reference wave, which improves the accuracy. The measurement accuracy and repeatability of the interferometer device itself.

Description

On-line detection method for wave aberration of projection objective lens in lithography machine

technical field

The invention relates to an optical performance detection method of a projection optical system, in particular to an online detection method for wave aberration of a projection objective lens of a lithography machine.

Background technique

The projection exposure device is used in the preparation process of large-scale integrated circuits, and the pattern on the mask is reduced and projected on the silicon wafer coated with photoresist through the projection objective lens. With the application of resolution enhancement technologies such as phase-shift masks and off-axis illumination, the process factor is gradually approaching the limit of the process, and the requirements for feature size control and overlay accuracy are getting higher and higher. The wave aberration of the projection objective lens, especially the advanced aberration, has more and more influence on the control error of the feature size. Therefore, it is necessary to develop an online detection device for the wave aberration of the projection objective lens to perform fast and high-precision online detection and correction of the wave aberration.

The traditional projection objective aberration measurement method usually images a specific pattern on the test mask on the image surface of the projection objective lens, uses a scanning electron microscope to measure the image developed on the silicon wafer, and calculates the aberration of the projection objective lens based on the measurement results data. This method needs to develop the silicon wafer, so the measurement time is long, and the measurement accuracy is low due to the errors in the process of gluing, developing and other processes during the measurement. In order to avoid these problems, a method of using interferometry has been proposed. An interferometer is installed on the photolithography machine to detect the wave aberration of the projection objective lens on-line. The interferometry methods used by international mainstream lithography equipment suppliers include Point Diffraction Interferometer (PDI), Slit Diffraction Interferometer (Line Diffraction Interferometer, LDI) and Shearing Interferometer (Lateral Shearing Interferometer, LSI). )etc. The aforementioned interferometric method has the advantages of fast detection speed, high precision, and good measurement repeatability; and it can be integrated in the lithography machine system to perform online detection of the full-field wave aberration of the projection objective lens, and obtain 36 items of each field point The wave aberration represented by the Zernike coefficient; and according to the detected 36 Zernike coefficients of each field point, the wave aberration can be corrected and controlled online. The above-mentioned interferometric method is the main development direction of the wave aberration detection technology of the projection objective lens of the lithography machine in the future.

In US Patent No. 2006/0262323, it is proposed to install PDI or LDI on the photolithography machine to detect the wave aberration of the projection objective lens online. In the aforementioned patent, the measurement principle of PDI is that a mask is placed on the image plane of the projection objective, and a circular hole with a diameter smaller than the diffraction limit resolution of the aforementioned projection objective system and a larger window are engraved on the mask; Diffraction occurs on the output beam of the projection objective lens, and an ideal spherical wave is generated as a reference wave; the window does not affect the output beam of the projection objective lens, and the output beam of the window carries the information of the wave aberration of the projection objective lens as a test wave; the test wave is collected by a photoelectric sensor such as a CCD and The interferogram of the reference wave; using interference fringe processing algorithms such as phase extraction, phase unwrapping, and wave surface fitting, the wave aberration of the projected objective mirror represented by a number of 36 Zernike coefficients is calculated. In the aforementioned patents, the principle of LDI is similar to that of PDI. A slit is used instead of a circular hole, and the slit is used to diffract the output beam of the projection objective lens, and an ideal spherical wave is generated in the one-dimensional direction of space as a reference wave; the reference wave is transmitted through the same window. The test wave carrying the wave aberration information of the projected objective lens interferes to form interference fringes; through two measurements in the orthogonal direction of space, two interferograms in the orthogonal direction are obtained; using phase extraction, phase unwrapping and wave surface fitting, etc. The interference fringe processing algorithm calculates the wave aberration of the projected objective lens represented by 36 Zernike coefficients.

Using the PDI or LDI interferometry method in the aforementioned patent to detect the wave aberration of the projection objective lens, due to the use of a circular hole or slit filter whose size is smaller than the diffraction limit resolution of the aforementioned projection objective lens, the light transmittance of the system is low, and the interference fringes The contrast is poor and the interferogram is noisy. This will seriously affect the accuracy of the aforementioned interference fringe processing algorithm, resulting in a decrease in the repetition accuracy of the wave aberration of the projection objective expressed by the calculated 36 Zernike coefficients. In the aforementioned patents, the moiré fringe method is used to process the interference fringes. This method uses computer simulation to simulate the same carrier frequency as the collected interferogram, and performs phase shift calculation on multiple simulated interferograms with fixed phase differences. In fact, it belongs to A single interferogram processing technology with fast detection speed.

Phase Shifting Interferometry (Phase Shifting Interferometry, PSI) introduces the synchronous phase detection technology in the communication theory into interferometry, and introduces an orderly phase shift between the two coherent lights of the interferometer through the stepping of the phase shifting device. The sampling of multiple interferograms can greatly suppress the influence of noise in the interferograms, and can also achieve high repeatability measurement accuracy when the contrast of the interference fringes is poor. However, PSI needs to control the phase shifting device to collect multiple interferograms step by step, and the detection speed is relatively slow. Fourier Transform Method (FTM) is a frequency-domain interference fringe processing method with high measurement accuracy, and only needs one carrier image, and the detection speed is fast, which is very suitable for online detection.

Contents of the invention

The technical problem to be solved by the present invention is to provide a fast and high-precision online detection method for wave aberration of projection objective lens.

The technical solution adopted in the present invention is: an interferometer device is integrated on the photolithography machine to perform online detection, correction and control of the wave aberration of the projected objective lens. The interferometer device is a point diffraction interferometer (PDI) or a slit diffraction interferometer (LDI), and has two measurement modes: PSI measurement mode and FTM measurement mode. The PSI measurement mode adopts phase-shifting interferometry, which has high measurement accuracy, and is mainly used for system error calibration of the interferometer device; the FTM measurement mode uses Fourier transform method to process interference fringes, and the measurement speed is fast, mainly in the projection objective lens wave aberration Used for online detection and control.

The present invention provides an online detection method for the wave aberration of the projection objective lens of a lithography machine. The system used in the method includes: a light source used to generate a projection beam; The illumination system; the projection objective lens capable of imaging the mask pattern on the silicon wafer; the mask workpiece stage capable of carrying the mask and positioning it precisely; the silicon wafer workpiece stage capable of carrying the silicon wafer and positioning it precisely; An interferometer device for detecting wave aberration of the projection objective.

In the above system, the interferometer device is a point diffraction interferometer or a slit diffraction interferometer. The interferometer device includes: a beam splitting device for splitting the beam emitted by the light source, such as a grating; a phase shifting device for driving the beam splitting device to introduce an orderly phase shift between the test wave and the reference wave , such as a piezoelectric ceramic micro-displacement stage; an object-space mask used to specify the measured field of view; an image-space mask used to generate test waves and spherical reference waves and to calibrate the system error of the interferometer device; used to collect The photoelectric sensor of the interference fringes of the test wave and the spherical reference wave, such as a CCD; a memory for storing the intensity information of the interference fringes collected by the photoelectric sensor; for calculating the system error of the interferometer device according to the data in the memory , the computing unit for the wave aberration of the projection objective lens and the adjustment amount of each compensator in the projection objective lens; it is used to control the adjustment of each compensator of the projection objective lens according to the data calculated by the computing unit to correct the aberration, and control The phase shifting device steps to realize the phase shifting controller.

The interferometer device has two measurement modes: the PSI measurement mode is used when calibrating the system error of the interferometer device; the FTM measurement mode is used when the wave aberration of the projected objective lens is detected and controlled online. Among them, the PSI measurement mode adopts phase-shifting interferometry, and the stepping of the phase-shifting device is used to obtain multiple interferograms, and the measurement accuracy is high; the FTM measurement mode uses the Fourier transform method to process interference fringes, and only one interferogram needs to be collected. Faster.

The interferometer device has a system calibration error function, which can calibrate the system measurement error introduced by the interferometer device itself.

产生参考波；窗孔的尺寸为

产生测试波；其中λ为所述光源的波长，NA_i为投影物镜像方数值孔径，σ为所述照明系统的部分相干因子，f为所述干涉仪装置测量的投影物镜出瞳波像差的空间频率范围。The image square mask has a wave aberration detection element and a system error calibration element. The wave aberration detection element of described square mask plate is made up of circular hole (or slit) and window; The size of circular hole (or slit) is less than

A reference wave is generated; the size of the aperture is

Generate a test wave; where λ is the wavelength of the light source, NA _i is the square numerical aperture of the projection object mirror, σ is the partial coherence factor of the illumination system, and f is the exit pupil wave aberration of the projection object measured by the interferometer device the spatial frequency range.

用来产生质量更高的球面波参考波，以标定所述干涉仪装置的系统误差。The system error calibration element of the described image square mask plate is made up of two circular holes (or slits); the first circular hole (or slit) is the same as the circular hole (or slit) of the wave aberration detection element on the image square mask plate slit) same size smaller than The size of the second circular hole (or slit) is less than

It is used to generate a spherical wave reference wave with higher quality to calibrate the system error of the interferometer device.

The method for online detection of wave aberration of the projection objective lens of the lithography machine comprises the following steps: adjusting the illumination field of view and the partial coherence factor of the illumination system on the lithography machine equipped with the interferometer device, so that the interferometer device Interference fringes with high contrast can be collected; in the PSI measurement mode, use the systematic error calibration element on the image square mask to calibrate the systematic error of the interferometer device; in the FTM measurement mode, use the image square The wave aberration detection element of the square mask performs online detection of the wave aberration of the projection objective lens; the aberration correction of the projection objective lens is automatically completed by using the controller of the interferometer device.

Compared with the detection method in U.S. Patent 2006/0262323, the present invention uses an interferometer device with two measurement modes for on-line detection of wave aberration: when calibrating the system error of the interferometer device, the PSI measurement mode is used; When aberration is detected and controlled online, the FTM measurement mode is adopted. On the premise of not reducing the detection speed, the measurement accuracy is improved. In addition, the method for calibrating the system error of the interferometer device proposed by the present invention uses a higher-quality spherical reference wave to calibrate the system error caused by each component of the interferometer device without reducing the contrast of the interference fringes, thereby improving the accuracy of the interferometer device. inherent measurement accuracy and repeatability.

Description of drawings

FIG. 1 is a schematic structural diagram of a photolithography machine and an interferometer device according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a beam splitting device 201 according to Embodiment 1 of the present invention;

FIG. 3 is a schematic diagram of an object-space mask 203 according to Embodiment 1 of the present invention;

FIG. 4 is a schematic diagram of an image square mask 204 according to Embodiment 1 of the present invention;

FIG. 5 is a schematic diagram of a beam splitting device 201 according to Embodiment 2 of the present invention;

FIG. 6 is a schematic diagram of an object-space mask 203 according to Embodiment 2 of the present invention;

FIG. 7 is a schematic diagram of an image square mask 204 according to Embodiment 2 of the present invention;

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

FIG. 1 is a schematic structural diagram of a photolithography machine and an interferometer device according to an embodiment of the present invention. The main components of the lithography machine 100 are: a light source 101 , an illumination system 102 , a mask plate 103 , a mask workpiece stage 104 , a projection objective lens 105 , a silicon wafer 106 and a silicon wafer workpiece stage 107 . The main components of the interferometer device are: beam splitting device 201 , phase shifting device 202 , object space mask 203 , image space mask 204 , photoelectric sensor 205 , memory 206 , computing unit 207 and controller 208 . The interferometer device 200 is integrated on the lithography machine 100 to realize online detection, correction and control of the wave aberration of the projection objective lens 105 in the lithography machine 100 .

Firstly, the working principle of the photolithography machine 100 will be described. After passing through the illumination system 102, the light emitted by the light source 101 is illuminated on the mask plate 103, and the pattern on the mask plate 103 is projected onto the silicon wafer 106 coated with photoresist in a step-and-scan manner through the projection objective lens 105. Realize pattern transfer. The light source 101 is an excimer laser light source, for example, an ArF excimer laser with a wavelength of about 193 nm or a KrF excimer laser with a wavelength of about 248 nm. The illumination system has a field diaphragm for adjusting the size of the illumination field of view and an aperture diaphragm for adjusting the distribution of the illumination beam, thereby adjusting the coherence factor of the illumination part. In addition, the illumination system also includes a large number of other optical elements, such as a fly-eye lens array, etc., so that the illumination on the mask plate 103 has ideal uniformity. The mask plate 103 engraved with the circuit pattern to be transferred is supported and driven by the mask workpiece stage 104 ; the silicon wafer 106 coated with photoresist is supported and driven by the silicon wafer workpiece stage 107 . The mask plate 103 and the silicon wafer 106 are located on the optical conjugate plane of the projection objective lens 105 . The mask workpiece stage 104 and the silicon wafer workpiece stage 107 move synchronously at different speeds, and accurately project and transfer the pattern of the mask plate 103 to the silicon wafer 107 coated with photoresist through the projection objective lens 105 in a step-scan manner . The wave aberration of the projection objective lens 105, especially the high-order aberration therein, will seriously affect the control accuracy of the transferred pattern feature size.

Example 1

In this embodiment, an interferometer device 200 based on the principle of point diffraction interference is integrated on the lithography machine 100 to detect the wave aberration of the projection objective lens 105 online. As shown in FIG. 1 , the interferometer device 200 is structurally composed of two parts 200 a and 200 b : 200 a is integrated on the mask workpiece stage 104 , and 200 b is integrated on the silicon wafer workpiece stage 107 . The working principle of the interferometer device in this embodiment will be described below. The light beam emitted by the light source 101 is first shaped by the illumination system 102 and irradiated onto the beam splitting device 201. In this embodiment, the beam splitting device 201 is a binary grating prepared by electron beam exposure of a chromium mask, and the base material is fused silica. The light-shielding layer is metal chromium, and the chromium layer is engraved with a periodic structure with a duty ratio of 1:1, as shown in FIG. 2 . After the light beam passes through the periodic structure of the binary grating, several diffraction orders are formed on the object-space mask 203 . The phase shifting device 202 is a piezoelectric ceramic micro-stage, which is used to drive the binary grating to step in a direction perpendicular to the grating lines, so as to introduce a phase difference in the high-order diffracted light of the binary grating.

The object space mask 203 is supported and driven by the mask workpiece table 104, and is also prepared by electron beam exposure chromium mask, the base material is fused silica, the light blocking layer is metal chromium, and a circular hole 209a and a relatively The large window 209b, as shown in FIG. 3, is used to select specific two diffraction orders as test waves and reference waves to enter the projection objective. The circular hole 209 a filters the incident light beam, eliminates the aberration caused by the optical elements such as the illumination system 102 in front of the object-space mask 203 , and the spherical wave generated by diffraction enters the projection objective lens 105 to be measured. The diameter d _o of the circular hole 209a satisfies formula (1), and is smaller than the resolution of the diffraction limit of the incident beam.

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; \&le;</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In formula (1), λ is the wavelength of the light source 101, NA _o is the object-side numerical aperture of the projection objective lens 105, and σ is the partial coherence factor of the illumination system 102, which can be calculated according to formula (2).

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; il</span>}}}{{\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In formula (2), NA _il is the numerical aperture of the illumination system 102 on the side of the mask 103 . It can be seen from formulas (1) and (2) that by reducing the σ of the illumination system 102, the diameter of the circular hole 209a can be increased, the system transmittance of the interferometer device can be increased, and the interference fringes collected by the photoelectric sensor 205 can be improved. contrast.

The width of the window 209b affects the light intensity of the transmitted beam, thereby affecting the contrast of the interference fringes. The optimal width of the window 209b should be selected according to the contrast of the interference fringes.

The image-side mask 204 and the object-side mask 203 are located on the optical conjugate plane of the projection objective 105 . The image square mask 204 is supported and driven by the silicon wafer workpiece stage 107, and is also prepared by electron beam exposure chrome mask, the base material is fused silica, the light-blocking layer is metal chromium, and the wave aberration detection element 210 and The system error calibration component 211 is shown in FIG. 4 .

The wave aberration detection element 210 of the image square mask 204 includes a circular hole 210b and a window 210a. The outgoing light beam from the window 209b on the object mask 203 passes through the projection objective lens 105 and is incident on the circular hole 210b. The incident light beam not only carries the aberration information of the projection objective lens 105, but also carries the aberration information of components such as the illumination system 102. After the information is filtered by the circular hole 210b, it is diffracted to generate a spherical reference wave. The diameter d _i1 of the circular hole 210b satisfies the formula (3), which is smaller than the resolution of the diffraction limit of the incident beam, and NA _i is the image square numerical aperture of the projection objective lens 105 .

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&le;</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The outgoing light beam from the circular hole 209a on the object-side mask 203 passes through the projection objective lens 105 and is incident on the window 210a. This incident light beam only carries the aberration information of the projection objective lens 105. The spherical reference wave generated by the diffraction of the hole 210 b interferes to form interference fringes on the photoelectric sensor 205 . The width w _i of the window 210a depends on the spatial frequency f of the exit pupil wave aberration of the projection objective lens to be measured, as shown in formula (4).

${\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; f\&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

The systematic error calibration element 211 of the image square mask 204 is composed of two circular holes. The diameter of the circular hole 211b satisfies formula (3), and is the same as the diameter d _i1 of the circular hole 210b , diffracts the light beam exiting the window 209b , and produces the same spherical reference wave. The diameter d _i2 of the circular hole 211a satisfies the formula (5), which is smaller than the resolution of the diffraction limit of the projection objective lens 105, diffracts the outgoing light beam of the circular hole 209a, and produces a higher-quality spherical reference wave, which is the same as the spherical reference wave produced by the circular hole 211b Interference, forming interference fringes on the photoelectric sensor 205 , and calibrating the systematic error of the interferometer device 200 .

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&le;</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The photoelectric sensor 205 can be a CCD sensor working in the deep ultraviolet band, which is integrated in the silicon workpiece stage 107 to detect interference fringes, record the intensity information of the interference fringes, and store them in the memory 206 . The arithmetic unit 207 stores a series of algorithms such as interference fringe processing, system error calibration, and computer-aided adjustment algorithm, and calculates the wave image of each viewing field point of the projection objective lens according to the interference fringe intensity information of each viewing field point of the projection objective lens stored in the memory 206 difference, and the adjustment amount of each compensator of the projection objective lens, and then adjust the projection objective lens through the controller 208 to correct the aberration.

When using the wave aberration detection element 210 to detect the wave aberration of the projection objective lens 105, the interferometer device 200 adopts the FTM measurement mode and uses the Fourier transform method to extract the phase information from the intensity information of the interference fringes. The Fourier transform method is a frequency-domain interference fringe processing method. The main steps include: denoising and extension of the interference fringe; two-dimensional Fourier transform to obtain the fringe spectrum; filter and move to the center of the frequency domain; The wrapped phase of the outgoing wavefront. Through phase unwrapping, the wrapped phase of the wavefront is expanded into continuous phases, and the wave aberration of the field of view point of the projection objective is obtained, and expressed as 36 Zernike coefficients by the wavefront fitting algorithm. The FTM measurement mode only needs one interferogram to calculate the wave aberration represented by 36 Zernike coefficients at a point of view of the projection objective lens 105, and the detection speed is fast; by choosing a better denoising and continuation algorithm, filter algorithm As well as the phase unwrapping algorithm, FTM can achieve high measurement accuracy. The wave aberration W ₁ detected by the wave aberration detection element 210 includes not only the wave aberration W _PO of the projection objective 105 but also the systematic error of the interferometer device 200 , as shown in formula (6).

W ₁ ＝W _PO +W _R1 +W _T1 +W _T2 +W _S (6)

In formula (6), W _R1 is the residual aberration of the spherical reference wave filtered by the circular hole 210b, which is mainly caused by the insufficient roundness of the circular hole 210b and the light beam passing through the fused silica substrate of the image square mask 204; W _T1 is the residual aberration of the spherical wave after filtering by the hole 209a, which is mainly caused by the insufficient roundness of the round hole 209a and the fused silica substrate of the light beam passing through the object mask 203; W _T2 is when the test light passes through the window 210a , the error caused by the fused silica substrate of the image square mask 204; W _S is the systematic error caused by the components of the interferometer device 200, mainly including the system geometric coma of the interferometer device 200, the processing and assembly of the grating 201 errors and aberrations caused by the installation error of the photoelectric sensor 205 . The above systematic errors will affect the measurement accuracy of the interferometer device.

Using the system error calibration component 211 to calibrate the system error of the interferometer can effectively improve the detection accuracy of the interferometer device. When performing system error calibration, since the circular hole 211a is used instead of the window 210a, the transmittance of the system decreases, and there is a large noise in the interferogram collected by the photoelectric sensor 205, which will directly affect the contrast of the interference fringe, and PSI measurement is required mode, using phase-shifting interferometry to perform high-precision phase-resolution calculations to suppress the influence of interferogram noise. At the same time, in the PSI measurement mode, the system error calibration component 211 uses a circular hole 211a with a diameter of d _i2 to calibrate the system error of the interferometer device 200, which eliminates the reference caused by the increase of the diameter d _i1 of the circular hole 210b in the FTM measurement mode. The influence of wave quality degradation, thereby improving the measurement accuracy and repeatability of the interferometer device 200.

Phase-shifting interference is realized in the interferometer device 200 through the following steps: firstly, the controller 208 is used to drive the silicon wafer workpiece table 107 to move, so that the circular holes 211a and 211b are respectively aligned with their respective incident light beams, and the photoelectric sensor 205 can collect and stored in the memory 206; the phase shifter 202 drives the grating 201 to step in the direction perpendicular to the grating 201 line, thereby introducing a phase difference in the high-order diffracted light of the binary grating; utilizes the photoelectric sensor 205 to collect The interferogram is stored in the memory 206; the above steps are repeated to store multiple phase-shifted interferograms; the multiple interferogram phase extraction algorithm is used to solve the phase to obtain the wrapping phase of the wavefront; through the phase unwrapping algorithm, the wrapping phase of the wavefront It is expanded into a continuous phase, and expressed as 36 Zernike coefficients with the wave surface fitting algorithm. The wavefront phase _W2 calculated in the above steps is the wavefront phase difference between the diffracted spherical waves of the circular hole 211a and the circular hole 211b, as shown in formula (7).

W ₂ ＝W _R1 +W _R2 +W _T3 +W _S (7)

In formula (7), W _R2 is the residual aberration of the spherical reference wave filtered by the circular hole 211a; W _T3 is the error caused by the fused silica substrate of the square mask 204 after the light beam is diffracted by the circular hole 211a. After approximation, It can be considered that W _T3 ≈W _T2 .

The system error calibration of the interferometer device 200 is completed by subtracting the corresponding Zernike coefficients of W ₁ and W ₂ to obtain the finally measured wave aberration W of the projection objective 105 , as shown in formula (8).

W W ₁ W ₂ ≈W _PO -W _R2 +W _T1 (8)

After system error calibration, the system error _WS of the interferometer device 200 is eliminated, and the detection result W only includes errors W _R2 and W _T1 . Since the diameter d _i2 of the circular hole 211a is smaller than the diameter d _i1 of the circular hole 210b, the quality of the spherical reference wave generated after filtering by the circular hole 211a is higher, and it can be deduced that W _R2 <W _R1 , which further improves the measurement accuracy of the interferometer device 200 .

The steps of the online detection method for the wave aberration of the projection objective lens of the lithography machine proposed in this embodiment are summarized as follows:

1) Adjust the illumination field of view and partial coherence factor σ of the illumination system 102, so that the interferometer device 200 can collect interference fringes with higher contrast;

2) In the PSI measurement mode, use the systematic error calibration element 211 of the image square mask 204 to calibrate the systematic error of the interferometer device 200;

3) In the FTM measurement mode, use the wave aberration detection element 210 of the image square mask 204 to perform online detection of the wave aberration of the full field of view of the projection objective 105, and obtain the wave aberration represented by 36 items of Zernike at each field of view of the projection objective 105. Aberration, and the adjustment amount of each compensator of the projection objective lens 105;

4) Use the controller 208 of the interferometer device 200 to automatically complete the aberration correction of the projection objective lens 105 .

Example 2

In this embodiment, an interferometer device 200 based on the principle of slit diffraction interference is integrated on the lithography machine 100 to detect the wave aberration of the projection objective lens 105 online. The slit diffraction interferometer in this embodiment is similar in principle and structure to the point diffraction interferometer in Embodiment 1. The system error calibration method is similar to the wave aberration detection method. The differences are as follows.

In the principle of interferometer measurement, this embodiment uses a slit instead of the round hole in Embodiment 1, and uses the slit to diffract the output beam of the projection objective lens, and an ideal spherical wave is generated in the one-dimensional direction of space as a reference wave. The wave aberration of the projection objective lens is obtained by two measurements in the space orthogonal direction;

In terms of the structure of the interferometer device 200, the difference between this embodiment and Embodiment 1 has the following aspects:

1) The beam splitting device 201 is a binary grating, and the directions of the scribe lines are two directions orthogonal to each other, as shown in FIG. 5 .

2) The phase shifting device 202 is a two-dimensional piezoelectric ceramic micro-stage, which is used to drive the binary grating to step in two orthogonal directions perpendicular to the grating lines, so as to introduce a phase into the advanced diffracted light of the binary grating Difference.

3) The chromium layer of the object-space mask 203 is engraved with slits and windows in two orthogonal directions, as shown in FIG. 6 , used to select two specific diffraction orders as test waves and reference waves to enter the projection objective lens . The widths of the slits 209c and 209e satisfy the formula (1), which is the same as the diameter d _o of the circular hole 209a. In the two measurements, spherical waves are generated in the one-dimensional direction of space and enter the projection objective lens 105 to be measured. The widths of the windows 209d and 209f affect the light intensity of the transmitted beams, thereby affecting the contrast of the interference fringes. The optimal widths of the windows 209d and 209f should be selected according to the contrast of the interference fringes. The lengths L _o of 209c, 209d, 209e and 209f are the same, and should be as long as possible, so that the light intensity of the transmitted beam increases, thereby improving the contrast of the interference fringes.

4) The wave aberration detection element 210 of the image square mask 204 is engraved with slits and windows in two orthogonal directions, as shown in FIG. wave aberration. The widths of the slits 210d and 210f satisfy the formula (3), which is the same as the diameter d _i1 of the circular hole 210b, and generate spherical reference waves in the one-dimensional direction of space in the two measurements respectively. The widths of windows 210c and 210e satisfy formula (4), are the same as the width _wi of window 210a, and depend on the spatial frequency f of the exit pupil wave aberration of the projection objective lens to be measured. The lengths L _i of 210c, 210d, 210e and 210f are the same, satisfying the formula (9), where m is the magnification of the projection objective lens 105 .

L _i =L _o m (9)

5) The system error calibration element 211 of the image square mask 204 is composed of two groups of slit pairs in the orthogonal direction, as shown in FIG. . The widths of the slits 211d and 211f satisfy the formula (3), and are the same as the widths of the slits 210d and 210f, and the spherical reference waves generated in the two orthogonal directions of measurement are also the same. The width of the slits 211c and 211e satisfies the formula (5), which is the same as the diameter d _i2 of the circular hole 211a, and generates higher-quality spherical reference waves in the one-dimensional direction of space to calibrate the systematic error of the interferometer device 200 .

When detecting the wave aberration of the projection objective lens 105, this embodiment also adopts the FTM measurement mode, and uses the Fourier transform method to extract the phase information from the intensity information of the interference fringes. The difference is that this embodiment needs to perform two measurements in the orthogonal direction, calculate the phase gradient of the wave surface in the two orthogonal directions, and then use the differential Zernike polynomial wave surface fitting algorithm to obtain the projection represented by 36 Zernike coefficients The wave aberration W ₁ of the objective lens 105 .

When calibrating the systematic error of the interferometer device 200 , this embodiment also adopts the PSI measurement mode, uses phase-shifting interferometry to perform high-precision phase resolution calculation, and suppresses the influence of interferogram noise. The difference is that this embodiment needs to perform two measurements in the orthogonal direction, calculate the phase gradient of the wave surface in the two orthogonal directions, and use the differential Zernike polynomial wave surface fitting algorithm to obtain the wave surface represented by 36 Zernike coefficients Plane phase W ₂ ; then subtract the corresponding Zernike coefficients of W ₁ and W ₂ to obtain the final measured wave aberration W of the projection objective lens 105.

Claims (6)

1. a photolithography machine projection object lens wave aberration online detection method, it is characterized in that: described method comprises the following steps: 1) Integrating an interferometer device (200) based on the principle of point diffraction interference on the lithography machine (100), and performing online detection of the wave aberration of the projection objective lens (105); 2) adjusting the illumination field of view and partial coherence factor σ of the illumination system (102), so that the interferometer device (200) can collect interference fringes with high contrast; 3) A circular hole (209a) and a larger window (209b) are engraved on the chromium layer of the object space mask (203), which are used to select two specific diffraction orders as test waves and reference waves entering the projection objective lens ( 105); 4) A wave aberration detection element (210) and a system error calibration element (211) are engraved on the chromium layer of the image square mask (204), and the wave aberration detection element (210) includes a circular hole (210b) and a window (210a ), the system error calibration element (211) is made up of two circular holes (211a) and (211b); 5) Adjust the interferometer device (200) to the PSI measurement mode, use the system error calibration component (211) of the image square mask (204), and calibrate the system error of the interferometer device (200); 6) Adjust the interferometer device (200) to the FTM measurement mode, and use the wave aberration detection element (210) of the image square mask (204) to perform online detection of the wave aberration of the projection objective (105) in the full field of view, and obtain The wave aberration represented by 36 items of Zernike at each field of view point of the projection objective (105), and the adjustment amount of each compensator of the projection objective (105); 7) Using the controller (208) of the interferometer device (200), the aberration correction of the projection objective lens (105) is automatically completed. 2. The method according to claim 1, characterized in that: the diameter d _o of the circular hole (209a) satisfies the formula (1), which is less than the resolution of the diffraction limit of the incident beam: ${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; \&le;</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ Wherein, λ is the wavelength of the light source (101), NA _o is the object-side numerical aperture of the projection objective lens (105), and σ is the partial coherence factor of the illumination system (102), and the calculation formula is: $\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; il</span>}}}{{\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ Wherein, NA _il is the numerical aperture of the illumination system (102) on the mask plate (103) side; The diameter d _i1 of the circular hole (210b) satisfies the formula (3), which is smaller than the resolution of the diffraction limit of the incident beam, and NA _i is the image square numerical aperture of the projection objective lens (105): ${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&le;</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ The width w _i of the window (210a) depends on the spatial frequency f of the exit pupil wave aberration of the projection objective lens to be measured, as shown in formula (4): ${\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; il</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; f\&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$ The diameter of the circular hole (211b) satisfies formula (3), is the same as the diameter d _i1 of the circular hole (210b), and the diameter d _i2 of the circular hole (211a) satisfies formula (5), which is smaller than the resolution of the diffraction limit of the projection objective lens (105) Rate. ${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&le;</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; NA</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$ 3. The method according to claim 1, characterized in that: in the FTM measurement mode, by reducing the σ of the illumination system (102), the diameters of the circular hole (209a) and the circular hole (210b) can be increased to improve the interference The system transmittance of the instrument device (200), thereby improving the contrast of the interference fringes collected by the photoelectric sensor (205) during the online detection of wave aberration; in the PSI measurement mode, the system error calibration component (211) adopts a diameter of The circular hole (211a) of d _i2 calibrates the systematic error of the interferometer device (200), eliminates the influence of the decrease in the quality of the reference wave caused by the increase of the diameter of the circular hole (210b) d _i1 in the FTM measurement mode, thereby improving the performance of the interferometer Measurement accuracy and repeatability of the device (200). 4. The method according to claim 1, characterized in that: the method can also use an interferometer device (200) based on the principle of slit diffraction interference to detect the wave aberration of the projection objective lens (105) on-line; the interferometer The object-side mask (203) chromium layer of the device (200) is engraved with slits (209c) and slits (209e), and windows (209d) and windows (209f) in two orthogonal directions; the interferometer device The wave aberration detection element (210) and the system error calibration element (211) are engraved on the chromium layer of the image square mask (204) of (200); the wave aberration detection element (210) consists of two narrow slit (210d) and slit (210f), and window (210c) and window (210e); the system error calibration element (211) is composed of two sets of slit pairs in orthogonal directions, wherein one set of slit pairs is slit (211c) and slit (211d), another set of slit pair is slit (211e) and slit (211f). 5. The method according to claim 4, characterized in that: the width of the slit (209c) and the slit (209e) satisfies formula (1), and is identical to the diameter d _o of the circular hole (209a); the slit (210d ) and the width of the slit (210f) satisfy the formula (3), which is the same as the diameter d _i1 of the circular hole (210b); the width of the window (210c) and the window (210e) satisfies the formula (4), and the The width w _i is the same; the width of the slit (211d) and the slit (211f) satisfies formula (3), and is identical with the width of the slit (210d) and (210f); the slit (211c) and the slit (211e) The width satisfies formula (5), and is the same as the diameter di ₂ of the circular hole (211a). 6. The method according to claim 4, characterized in that: in the FTM measurement mode, by reducing the σ of the illumination system (102), the slit (209c), slit (209e), slit ( 210d) and the width of the slit (210f), improve the system transmittance of the interferometer device (200), thereby improving the contrast of the interference fringes collected by the photoelectric sensor (205) when the wave aberration is detected online; in the PSI measurement mode Next, the system error calibration component (211) adopts the slit (211c) and slit (211e) with a width of d _i2 to calibrate the systematic error of the interferometer device (200), eliminating the slit (210d) and The increase of the width d _i1 of the slit (210f) reduces the quality of the reference wave, thereby improving the measurement accuracy and repeatability of the interferometer device (200).

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