CN102261985B - Optical system wave aberration calibration apparatus and calibration method of using apparatus to test error - Google Patents

Abstract

The optical system wave aberration calibration device and the calibration method of the test error of the device relate to the field of optical measurement technology, which solves the problem that the existing optical system cannot evaluate whether the test error meets the detection accuracy requirements before the detection of optical components and selects a suitable phase shifting algorithm For the problem of processing the collected data, the light splitting system of the present invention emits two beams of orthogonal linearly polarized light with a common optical path, exits the polarization beam splitter prism, and then couples to the reference optical fiber through the coupling lens, the two diffracted by the reference optical fiber The spherical wave interferes to obtain the interferogram; the photoelectric detector is used to collect and transmit to the computer, and the piezoelectric ceramic is used to shift the phase, and the photodetector collects multiple interferograms; the thirteen-step phase shift algorithm is used for data processing and analysis , the test error is obtained, and the invention realizes ultra-high-precision detection of the wave aberration of the optical system.

Description

Calibration device for optical system wave aberration and calibration method for test error of the device

technical field

The invention relates to the technical field of optical measurement, in particular to a calibration device for wave aberration of an optical system and a calibration method for testing errors of the device.

Background technique

Extreme ultraviolet lithography is a next-generation lithography technology based on traditional optical lithography, which inherits the development achievements of current optical lithography to the greatest extent. The working wavelength of extreme ultraviolet lithography is the extreme ultraviolet band of 13-14nm. There are major differences between traditional optical lithography and detection technology. As one of the core unit systems of the lithography machine, in order to achieve the requirements of lithography resolution and critical dimension control, the RMS wave aberration of the optical system should be less than λ/20. Such a high-precision optical system requires a higher-precision detection device. At present, the more advanced interferometer products of Zygo and Wyko companies in the United States generally use standard spherical lenses to generate reference spherical waves. However, due to the impact of optical processing and assembly, As a result, the aberration of the reference spherical wave is greater than λ/50, which cannot be further reduced. This directly leads to the fact that the detection accuracy of the current interferometer can only reach λ/20-λ/50 (λ=632.8nm), which is far from satisfying Detection requirements for wave aberration of extreme ultraviolet lithography projection objective lens system.

Therefore, finding an ultra-high-precision reference spherical wave has become a key issue in improving the measurement accuracy of the detection device.

Raymond N. Smart and J. Strong invented the point diffraction interferometer in 1972. It uses the approximately ideal spherical wave generated by pinhole diffraction as a reference wave to eliminate the influence of the reference wave surface error of the conventional interferometer and greatly improve the detection accuracy. . With the continuous improvement of optical detection requirements, point diffraction interferometers are increasingly showing their advantages, and are widely used in high-precision optical detection, which provides the possibility for high-precision detection of wave aberration in extreme ultraviolet lithography projection objective system .

Although the point diffraction interferometer solves the problem of referring to spherical waves, some error sources in the point diffraction interferometer, such as the instability error of the light source, the nonlinear error of the photodetector, the quantization error of the photodetector, and the environment error, are still This limits the detection accuracy of the interferometer.

In 1974, Bruning et al. proposed phase-shifting interferometry. He introduced the synchronous phase detection technology in communication theory into optical interferometry technology, which is a major development in computer-aided interferometry technology. The principle is to introduce an orderly displacement between the phase differences of two coherent lights of the interferometer, and when the reference optical path (or phase) changes, the position of the interference fringes also moves accordingly. In this process, the photoelectric detector is used to sample the interferogram, and the image acquisition card is digitized to obtain a digital signal that can be processed by the computer. Finally, the computer obtains the phase distribution according to the change of light intensity according to a certain mathematical model. The advantages of phase-shifting interferometry are simple calculation, fast speed and high precision. The key technology is to analyze and process the measured data by computer to obtain the measured phase value.

In order to realize the development of optical detection to ultra-high precision, the organic combination of point diffraction interferometer and phase-shifting interferometry is undoubtedly an inevitable trend.

A phase-shifting point diffraction interferometer is composed of a small hole plate on the object plane, a transmission grating, a small hole plate on the image plane and a photodetector. After the elements or systems converge, they will diffract through the transmission grating and form several diffraction orders on the small hole plate on the image plane, so that the +1 order (or 0 order) diffracted light will be diffracted through a small hole on the small hole plate on the image plane to produce an ideal The spherical wave is used as the reference light, and the 0th order (or +1st order) diffracted light passes through a window on the small hole plate on the image plane as the test light, and the other diffraction orders are blocked by the opaque part of the small hole plate on the image plane. The test light and the reference light form interference fringes on the photodetector, and the phase shift is realized by moving the transmissive grating laterally, and the phase shift algorithm is used to analyze the fringes, which improves the measurement accuracy.

Another phase-shifting point diffraction interferometer places the transmission grating in front of the small hole plate on the object surface. The small hole plate on the object surface contains a small hole and a larger window. The 0th order diffracted light passes through the small hole to generate an ideal spherical wave, + The 1st order diffracted light passes directly through the window. After the two beams of light pass through the optical element or system under inspection, they are focused onto the small hole plate on the image plane, where the 0th order diffracted light passes through the window as the test light, and the +1st order diffracted light passes through the small hole as the reference light. Both beams of the point-diffraction interferometer are only filtered through a pinhole once, which increases the light intensity of the reference light and improves the fringe contrast compared with the former point-diffraction interferometer.

In 2005, Gary E. Sommargren in the patent US6909,510 B2 "Application of the phase shifting diffraction interferometer for measuring convex mirrors and negative lenses" used the end faces of two flexible cores instead of small holes to form a dual-fiber point diffraction interferometer. The emitted light irradiates the end face of the reference fiber through the optical element under test, and after reflection interferes with the diffracted wave emitted by the reference fiber, forming interference fringes on the photodetector through the imaging lens, and the detection device introduces a phase shift in the test optical path, and finally The dual-fiber phase-shift point diffraction interferometer realizes high-precision detection of convex and negative lenses.

However, the above-mentioned existing wave aberration detection device cannot evaluate the test error and whether the phase shift algorithm meets the detection accuracy requirements before the detection of the optical element or system, which may cause inaccurate detection results, thereby hindering the realization of ultra-high The detection of accuracy brings difficulties.

Contents of the invention

The present invention provides an optical system wave aberration calibration device and an The calibration method of the test error of the device.

An optical system wave aberration calibration device, the device includes a beam splitting system, a coupling lens, a reference fiber, a motorized polarization controller, a photodetector, a computer; the beam splitting system includes a laser, a neutral density filter, a half-wave plate, polarization beam splitter, first quarter-wave plate, second quarter-wave plate, first corner cube, second corner cube, first plane reflector and second plane reflector; The beam emitted by the laser is divided into two beams of orthogonal linearly polarized light after passing through a neutral density filter, a half-wave plate and a polarization beam splitter prism. The first beam of linearly polarized light passes through the first horizontal direction of the polarization beam splitter After the quarter-wave plate and the first corner cube, it is reflected to the polarization beam splitter by the first plane reflector; the second beam of linearly polarized light passes through the second quarter-wave plate and the second After the corner cube, it is reflected to the polarization beam splitter by the second plane mirror, and the light beam emitted by the polarization beam splitter is coupled into the reference fiber through the coupling lens, the polarization state of the light beam is controlled by the motorized polarization controller, and the photodetector receives the reference fiber The interferogram of the beam reflected by the end face is received by the computer.

A method for calibrating test errors of an optical system wave aberration calibrating device, the method is completed by the following steps:

Step 1. Two beams of orthogonal linearly polarized light with a common optical path emitted by the beam splitting system are emitted by a polarization beam splitter prism and then coupled into a reference fiber through a coupling lens. The two spherical waves diffracted by the reference fiber interfere to obtain an interference pattern;

Step 2. The interferogram obtained in step 1 is collected by a photodetector and then sent to the computer, and the piezoelectric ceramic is used for phase shifting, and the photoelectric detector collects multiple interferograms; data processing is performed using a thirteen-step phase shift algorithm Analyze to obtain test error;

The thirteen-step phase-shifting algorithm is:

$\mathrm{\&phi;}=\arctan \left(\frac{6(I_2-I_{12})+32(I_{10}-I_4)+58(I_6-I_8)}{-(I_1+I_{13})+17(I_3+I_{11})-47({\mathrm{<figure-callout\; id="5"\; label="I"\; filenames="HDA0000067882850000011.png"\; state="\{\{state\}\}">I</figure-callout>}}_5+I_9)+{62I}_7}\right)$ , the I _i (i=1...13) are the light intensities of the thirteen phase-shifting interferograms respectively.

The working principle of the present invention: the present invention is to judge whether the test components of the wave aberration of the optical system meet the accuracy requirements, and to calibrate the test error. By analyzing the interference pattern of two spherical waves directly diffracted by the same optical fiber, the wave aberration of the optical system is calibrated. The test error caused by the detector error in the aberration detection device, and judge whether it meets the detection accuracy requirements, and finally select the detector that meets the detection accuracy requirements; use different phase shifting algorithms to analyze multiple interferograms, so as to select the test error The thirteen-step algorithm with strong suppression ability processes the interferogram data. By selecting appropriate test components and phase-shifting algorithms, ultra-high-precision detection of wave aberrations in optical systems can be realized.

Beneficial effects of the present invention: the present invention utilizes computer processing to calibrate the measurement error introduced by the detector error, so that the test components that meet the detection accuracy requirements can be selected. Collect multiple interferograms and use the thirteen-step phase-shift algorithm for data processing, and finally can achieve ultra-high-precision detection of wave aberration in the optical system.

Description of drawings

Fig. 1 is the schematic diagram of the optical system wave aberration calibration device described in the present invention;

In the figure: 1. Laser, 2. Neutral density filter, 3. Half wave plate, 4. Polarizing beam splitter, 5. First quarter wave plate, 6. Second quarter wave plate Wave plate, 7. First corner cube, 8. Second corner cube, 9. Piezoelectric ceramics, 10. First plane mirror, 11. Second plane mirror, 12. Coupling lens, 13. Reference fiber , 14, motorized polarization controller, 15, photodetector, 16, computer.

Detailed ways

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, this embodiment is described in conjunction with FIG. 1 , an optical system wave aberration calibration device, which includes a spectroscopic system, a coupling lens 12, a reference optical fiber 13, a motorized polarization controller 14, a photodetector 15, and a computer 16; The feature is that the spectroscopic system includes a laser 1, a neutral density filter 2, a half wave plate 3, a polarizing beam splitting prism 4, a first quarter wave plate 5, a second quarter wave plate 6. The first corner cube prism 7, the second corner cube mirror 8, the first plane reflector 10 and the second plane reflector 11; After the wave plate 3 and the polarization beam splitter 4, it is divided into two beams of orthogonal linearly polarized light, and the first beam of linearly polarized light passes through the first quarter-wave plate 5 and the first corner cube in the horizontal direction of the polarization beam splitter prism 4 After 7, it is reflected to the polarization beam splitter 4 through the first plane reflector 10; after the second light polarized light passes through the second quarter-wave plate 6 and the second corner cube prism 8 in the vertical direction of the polarization beam splitter prism 4, it passes through the second The two plane mirrors 11 are reflected to the polarization beam splitter 4, the light beam emitted by the polarization beam splitter 4 is coupled into the reference fiber 13 through the coupling lens 12, the electric polarization controller 14 controls the polarization state of the beam, and the photodetector 15 receives the reference fiber 13 The interferogram of the beam reflected by the end face is received by the computer 16 .

After the first beam of linearly polarized light described in this embodiment passes through the first quarter-wave plate 5 and the first corner cube 7 in the horizontal direction of the polarization splitter prism 4, the polarization direction of the first beam of linearly polarized light changes by 90° Spend.

After the second beam of linearly polarized light described in this embodiment passes through the second quarter-wave plate 6 and the second corner cube 8 in the vertical direction of the polarization splitter prism 4, the polarization direction of the second beam of linearly polarized light changes by 90 degrees .

The spectroscopic system described in this embodiment further includes a piezoelectric ceramic 9, and the piezoelectric ceramic 9 is used to move the second corner cube prism 8 to realize a phase shift with a step size of π/2.

Specific embodiment two, the calibration method of the test error of the optical system wave aberration calibration device, the method is completed by the following steps:

Step 1. Two beams of orthogonal linearly polarized light with a common optical path emitted by the beam splitting system are emitted by the polarization beam splitter prism 4 and then coupled into the reference fiber through the coupling lens 12. The two spherical waves diffracted by the reference fiber 13 interfere to obtain an interference pattern ;

Step 2. The interferogram obtained in step 1 is collected by the photodetector 15 and then sent to the computer 16, and the piezoelectric ceramic 9 is used for phase shifting. The photoelectric detector 15 collects multiple interferograms; using thirteen steps of phase shifting Algorithms for data processing and analysis to obtain test errors;

The thirteen-step phase-shifting algorithm is:

$\mathrm{\&phi;}=\arctan \left(\frac{6(I_2-I_{12})+32(I_{10}-I_4)+58(I_6-I_8)}{-(I_1+I_{13})+17(I_3+I_{11})-47(I_5+I_9)+{62I}_7}\right)$ , and the I _i (i=1...13) are the light intensities of the thirteen phase-shifting interferograms respectively.

The test error described in this embodiment is a test error caused by a detector error.

The motorized polarization controller 14 described in this embodiment controls the polarization states of the two common optical path beams to be the same.

The orthogonal linearly polarized lights of the two common optical paths described in this embodiment are coupled into the reference optical fiber 13 through the coupling lens 12 after exiting the polarization beam splitter prism 4, and the electric polarization controller 14 added to the reference optical fiber 13 is used to couple The polarization state of the light beam is controlled to make it consistent, and the two spherical waves diffracted from the reference optical fiber 13 interfere, and the interferogram is collected by the photodetector 15, and sent to the computer 16 for data processing and analysis according to the phase-shifting algorithm, and the result is obtained by The test error caused by the detector error. If the test error meets the requirements of the wave aberration detection accuracy of the optical system, then the detection can be carried out normally. Produce test components that meet the detection accuracy requirements;

In the above process, the relative intensity of the two beams of light can be adjusted by rotating the half-wave plate 3 and adjusting the motorized polarization controller 14 to achieve the best fringe contrast, and the first angular cone which is insensitive to the deflection error is introduced Prism 7 and second corner cube prism 8 adjust the optical path difference of the two beams of light by moving the first corner cube prism 7, and move the second corner cube prism 8 through piezoelectric ceramics 9 to realize a shift with a step size of π/2 phase, by introducing the second plane mirror 11 to make the measurement result insensitive to the lateral shift of the second corner cube 8 during the phase shifting process, and by introducing the first plane mirror 10 to realize the common optical path of the two beams. Since there is no tested component, the measurement result is only the test error introduced by the detector error. This process is used to evaluate whether the test error caused by the detector error meets the accuracy requirements, so as to determine the qualified test components. Finally, the ultra-high precision detection of wave aberration of the optical system is realized.

Claims (6)

1. optical system wavefront aberration caliberating device, this device comprises beam splitting system, coupled lens (12), reference optical fiber (13), electronic Polarization Controller (14), photodetector (15), computing machine (16); It is characterized in that said beam splitting system comprises laser instrument (1), neutral density filter (2), 1/2nd wave plates (3), polarization splitting prism (4), first quarter-wave plate (5), second quarter-wave plate (6), first prism of corner cube (7), second prism of corner cube (8), first plane mirror (10) and second plane mirror (11); The light beam of said laser instrument (1) outgoing is behind neutral density filter (2), 1/2nd wave plates (3) and polarization splitting prism (4); The linearly polarized light that is divided into two bundle quadratures; Behind first quarter-wave plate (5) and first prism of corner cube (7) of the first bunch polarized light through the horizontal direction of polarization splitting prism (4), reflex to polarization splitting prism (4) through first plane mirror (10); Behind second quarter-wave plate (6) and second prism of corner cube (8) of the second bunch polarized light through polarization splitting prism (4) vertical direction; Reflex to polarization splitting prism (4) through second plane mirror (11); The light beam of said polarization splitting prism (4) outgoing is coupled in the reference optical fiber (13) through coupled lens (12); The polarization state of electronic Polarization Controller (14) control bundle, the interferogram that photodetector (15) receives reference optical fiber (13) end face reflection light beam is received by computing machine (16).

2. optical system wavefront aberration caliberating device according to claim 1; It is characterized in that; Behind first quarter-wave plate (5) and first prism of corner cube (7) of the described first bunch polarized light through the horizontal direction of polarization splitting prism (4), its change of polarized direction 90 degree.

3. optical system wavefront aberration caliberating device according to claim 1; It is characterized in that; Behind second quarter-wave plate (6) and second prism of corner cube (8) of the described second bunch polarized light through first polarization splitting prism (4) vertical direction, its change of polarized direction 90 degree.

4. optical system wavefront aberration caliberating device according to claim 1 is characterized in that, said beam splitting system also comprises piezoelectric ceramics (9), adopts piezoelectric ceramics (9) to move second prism of corner cube (8) and realizes that step-length is the phase shift of pi/2.

5. test error scaling method according to the said optical system wavefront aberration caliberating device of claim 1 is characterized in that this method is accomplished by following steps:

Step 1, beam splitting system outgoing two bundles altogether the orhtogonal linear polarizaiton light of light path through polarization splitting prism (4) outgoing after overcoupling lens (12) be coupled in the reference optical fiber (13); Two spherical waves of said reference optical fiber (13) diffraction interfere, and obtain interferogram;

Step 2, the interferogram that step 1 is obtained are sent to computing machine (16) after adopting photodetector (15) to gather, and adopt piezoelectric ceramics (9) to carry out phase shift, and said photodetector (15) is gathered repeatedly interferogram; Adopt 13 step phase shift algorithms to carry out Data Management Analysis, obtain test error;

Said 13 step phase shift algorithms are:

$\mathrm{\&phi;}=\mathrm{Arctan}\left(\frac{6(I_2-I_{12})+32(I_0-I_4)+58(I_6-I_8)}{-(I_1+I_{13})+17(I_3+I_{11})-47(I_5+I_9)+{62I}_7}\right)$ , said I _i(i=1 ... 13) be respectively the light intensity of 13 width of cloth phase-shift interferences.

6. the scaling method of optical system wavefront aberration caliberating device test error according to claim 5 is characterized in that, the test error that said test error causes for the detector error.

Images