Wavefront aberration detection system and method for 193 nm objective

Abstract

The present application relates to lens detection technical field, specifically to a kind of wavefront aberration detection system and method for 193nm objective lens;A kind of wavefront aberration detection system for 193nm objective lens, comprising: optical system and support frame, optical system includes outgoing light path and return light path;Outgoing light path: by the light path connection of light source beam expansion system, self-separation coaxial light path, focusing component, objective lens to be measured and ball bowl composition;Return light path: by the light path connection of ball bowl, objective lens to be measured, shrink beam component, self-separation coaxial light path and Shack-Hartmann wavefront sensor composition;Self-separation coaxial light path is by polarizing beam splitter and 1 / 4 wave plate composition sequentially connected composition;Wherein, focusing component and shrink beam component use same coupling mirror;Self-separation coaxial light path output beam diameter is greater than the entrance pupil of coupling mirror 10mm;The numerical aperture of coupling mirror is greater than the object side numerical aperture of objective lens to be measured.The present application is simple in structure, completely adapts the detection and measurement wavelength requirement of Shack-Hartmann wavefront sensor.

Description

Technical Field

[0001] This invention relates to the field of lens inspection technology, and specifically to a wavefront aberration detection system and method for 193nm objectives. Background Technology

[0002] The two most commonly used methods for detecting objective wave aberrations are: 1) Detection using a laser interferometer: Interference occurs after the reference optical path and the test optical path are re-merged. An interferogram is captured by a camera, and the wavelet aberration is accurately calculated using a phase extraction algorithm.

[0003] 2) Detection using Shaker-Hartmann wavefront sensor: By comparing the convergence point of the microlens array with the regular lattice formed by the ideal plane wave, the spot offset in each sub-aperture is calculated, thereby reconstructing the slope distribution of the entire wavefront, and then obtaining the complete wave aberration through an integral algorithm.

[0004] Deficiencies in existing detection methods: 1) For laser interferometers, most existing laser interferometers have a laser output wavelength of 632.8nm. There are few existing laser interferometers for the ultraviolet band. This is because the manufacturing cost of laser interferometers for 266nm is high and the technology is unstable. Most importantly, some precision optical lenses have extremely high requirements for the wavelength of the laser source when performing wavelet aberration detection, and the existing laser interferometer detection schemes cannot meet the measurement conditions.

[0005] 2) Although the Shak-Hartmann wavefront sensor has a wide detection wavelength range, covering wavelengths from 157nm to 1700nm by selecting different light sources and detector types, the incident light window of the Shak-Hartmann wavefront sensor is generally small, with a diameter of about 12mm, which is far from sufficient for optical systems that require large-aperture mirror measurements. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defects existing in the prior art, thereby providing a wavelet aberration detection system and method for 193nm objectives.

[0007] A wavelet aberration detection system for a 193nm objective lens includes: an optical system and a support frame, wherein the optical system includes a forward optical path and a return optical path; Outbound optical path: Consists of a light source beam expanding system, a self-separating coaxial optical path, a focusing assembly, an objective lens under test, and a ball cup connected sequentially; The return optical path consists of a ball cup, the objective lens under test, the beam shrinking assembly, the self-separating coaxial optical path, and the Shaker-Hartmann wavefront sensor, which are connected sequentially by optical paths. The self-separating coaxial optical path is composed of a polarizing beam splitter prism and a quarter-wave plate connected in sequence. The focusing and beam-shrinking components use the same coupling mirror; the output beam diameter of the self-separating coaxial optical path is 10 mm larger than the entrance pupil of the coupling mirror. The numerical aperture of the coupling lens is greater than the object-side numerical aperture of the objective lens under test. All devices are adapted for a 193nm wavelength.

[0008] Preferably, the focus of the output beam of the coupling mirror is aligned with the focus of the objective lens under test.

[0009] Preferably, the 1 / 4 wave plate has a diameter of 12.5 mm.

[0010] A wavefront aberration detection method for a 193nm objective lens, comprising a wavefront aberration detection system for a 193nm objective lens, including: S1. Output 193nm laser using a light source beam expander system; S2. The 193nm laser is split using a polarizing beam splitter to obtain a first P-beam and a first S-beam; the first P-beam is transmitted to a quarter-wave plate, and the first S-beam is incident into air for extinction. S3. Use a quarter-wave plate to change the polarization angle of the first P-beam and transmit it to the coupling mirror; S4. The coupling lens focuses the center 10mm of the incident beam and outputs it to the objective lens under test; S5. The beam of light passing through the objective lens returns via the same path through the spherical cup; S6. The returned beam passes through the objective lens under test and is then incident on the coupling lens; S7. The coupling mirror performs beam reduction on the center 10mm of the returning beam and outputs it to a 1 / 4 wave plate; S8. Use a quarter-wave plate to convert the polarization angle of the returning beam to obtain the second S-beam; S9. The second S-beam is incident on the polarizing beam splitter and reflected by the polarizing beam splitter to the Shack-Hartmann wavefront sensor for wavefront aberration analysis.

[0011] Preferably, it also includes multiple mirrors, which are disposed at the input and output ends of the self-separating coaxial optical path.

[0012] Preferably, the diameter of the 193nm laser output by the light source beam expansion system is 25mm or 15mm.

[0013] Preferably, the numerical aperture of the spherical bowl is 0.9, which is greater than the numerical aperture of the mirror image of the object to be tested.

[0014] Preferably, the emission direction of the second S-beam does not coincide with the emission direction of the first S-beam.

[0015] Preferably, the optical path between the output end of the light source beam expander system and the input end of the coupling mirror is fixed inside the enclosed plate.

[0016] The technical solution of this invention has the following advantages: This invention solves the problem of insufficient receiving aperture in Shaker-Hartmann wavefront sensors through a clever optical coupling layout. Furthermore, the optical system layout of this invention improves upon the extremely high requirements of the objective lens under test for the laser wavelength used in traditional measurements, enabling the measurement results to meet the needs of precision measurement. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the optical system of the present invention; Figure 2 for Figure 1 Schematic diagram of the optical system from top view Figure 3 This is a front view of the overall structure of a wavefront aberration detection system for a 193nm objective lens according to the present invention. Figure 4 This is a top view of the overall structure of a wavefront aberration detection system for a 193nm objective lens according to the present invention. Figure 5 This is a side view of the overall structure of a wavelet aberration detection system for a 193nm objective lens according to the present invention.

[0019] Explanation of reference numerals in the attached figures: 13-Optical system; 14-Support frame; 1-193nm laser; 2-First beam expander; 3-Second beam expander; 4-First reflecting mirror; 5-Second reflecting mirror; 6-Polarizing beam splitter; 7-1 / 4 waveplate; 8-Third reflecting mirror; 9-Coupled mirror; 10-Objective lens under test; 11-Ball cup; 12-Shack-Hartmann wavefront sensor. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Example 1 like Figure 3-5 As shown, this embodiment discloses a wavefront aberration detection system for a 193nm objective lens, including: an optical system 13 and a support frame 14, wherein the optical system 13 includes a forward optical path and a return optical path; like Figure 1-2 As shown, the outgoing optical path consists of a light source beam expanding system, a self-separating coaxial optical path, a focusing assembly, the objective lens 10 under test, and a ball cup 11 connected in sequence. The return optical path consists of a ball cup 11, a test objective lens 10, a beam shrinking assembly, a self-separating coaxial optical path, and a Shaker-Hartmann wavefront sensor 12 connected in sequence. The self-separating coaxial optical path is composed of a polarizing beam splitter prism 6 and a quarter-wave plate 7 connected in sequence. The focusing component and the beam-shrinking component use the same coupling mirror 9; the output beam diameter of the self-separating coaxial optical path is 10 mm larger than the entrance pupil of the coupling mirror 9; The numerical aperture of the coupling lens 9 is greater than the numerical aperture of the objective lens 10. All devices are adapted for a 193nm wavelength.

[0023] Specifically: For light source beam expansion systems: It includes a laser and two beam expanders connected in sequence.

[0024] A 193nm laser 1 is used to provide the detection light source for the entire detection system. The 193nm laser 1 outputs a laser spot diameter of 1mm and an output laser power of 10mw.

[0025] Two beam-expanding schemes consisting of two beam expanders: Option 1: The first beam expander 2 expands the laser spot output by the 193nm laser 1 by 5 times; the second beam expander 3 expands the laser spot output by the first beam expander 2 by 5 times. Option 2: The first beam expander 2 expands the laser spot output by the 193nm laser 1 once; the second beam expander 3 expands the laser spot output by the first beam expander 2 a second time, and then expands the beam by 3 times. For self-separating coaxial optical paths: It is composed of a polarizing beam splitter 6 and a quarter-wave plate 7 connected together; For polarizing beam splitter 6: With a side length of 25mm, it can split 193nm laser light. The P-beam is transmitted and perpendicularly incident on the 1 / 4 wave plate 7, while the S-beam is reflected as stray light. The light is then extinct in the air using black light-absorbing paper.

[0026] For the 1 / 4 wave plate 7: With a diameter of 12.5 mm, the polarization angle of the incident light is changed. The first P-light enters the 1 / 4 wave plate 7 from the polarizing beam splitter 6. When the second S-light returns, it is equivalent to the P-light passing through the 1 / 4 wave plate 7 twice, thus converting the first P-light into the second S-light. After the returning first P-light becomes the second S-light, it enters the polarizing beam splitter 6 again. The polarizing beam splitter 6 reflects the second S-light, and the reflected light is perpendicularly incident on the Shack-Hartmann wavefront sensor 12. For coupling mirror 9: A 193nm coupling mirror was used to focus the laser spot after secondary beam expansion, so that the focal point of the 193nm coupling mirror coincided with the object-side focal point of the objective lens 10 under test. The entrance pupil of the coupling mirror 9 was 10mm, the numerical aperture NA=0.14, the back focal length was 14.67mm, and the total length was 47.86mm.

[0027] It should be noted that during actual operation, the output beam focus of the coupling mirror 9 and the focus of the objective lens 10 under test only need to be aligned.

[0028] For objective lens 10 under test: It uses a 193nm objective lens with an object-side numerical aperture (NA) of 0.138, an image-side numerical aperture (NA) of 0.552, an object-side focal length of 53.54mm, an image-side focal length of 3.1mm, and a total length of 1233.35mm.

[0029] For Bowl 11: The ball cup 11 has a numerical aperture NA of 0.9. The focal point of the ball cup 11 coincides with the image point of the objective lens 10 under test, and the first P-beam returns along the original path.

[0030] In practical applications, it also includes: multiple reflectors positioned at the input and output ends of the self-separating coaxial optical path; a support frame 14; and several adaptable adjustment platforms for adjusting the position of each component. The multiple reflectors specifically include: a first 193nm reflector, a second 193nm reflector, and a third 193nm reflector; The second beam expander 3 is optically connected to the first 193nm reflector, the second 193nm reflector, the polarizing beam splitter 6, the quarter-wave plate 7, and the third 193nm reflector in sequence.

[0031] like Figure 1 As shown, the first 193nm reflector, with a diameter of 50mm, changes the direction of light propagation and reflects the secondary expanded laser beam vertically upward. The second 193nm reflector, with a diameter of 50mm, changes the direction of light propagation, changing the direction of propagation of the secondary expanded laser spot to horizontal, and the vertically incident polarizing beam splitter 6. The third 193nm reflector, with a diameter of 50mm, changes the direction of light propagation, causing the laser beam that has been expanded by the second beam to be refracted and incident perpendicularly onto the coupling mirror 9; and causes the beam returning from the coupling mirror 9 to be refracted and incident perpendicularly onto the quarter-wave plate 7.

[0032] like Figure 2 As shown, the optical path between the output end of the light source beam expansion system and the input end of the coupling mirror 9 is fixed inside the enclosed plate.

[0033] Example 2 This embodiment discloses a wavefront aberration detection method for a 193nm objective lens, applying the wavefront aberration detection system for a 193nm objective lens from Embodiment 1, including: S1. A 193nm laser is output using a light source beam expansion system; the 193nm laser is generated by a 193nm laser 1, with a center wavelength of 193.368nm, an output laser spot diameter of 1mm, an output power of 10mw, and a divergence angle of 0.8mrad; the 193nm laser 1 is supported by a height-adjustable adjustment platform, and the Z-axis is adjustable for easy adjustment of the subsequent optical path.

[0034] After the 193nm laser beam is emitted, the optimal method is to achieve a 25X beam expansion effect using two 5X beam expanders, namely the first beam expander 2 and the second beam expander 3. The two sets of 5X beam expanders make the output laser beam more uniform, reduce the divergence angle of the emitted light, and decrease system stray light. Simultaneously, the beam expansion ratio can be changed; for example, replacing the second beam expander 3 with a different 5X beam expander 3 achieves a 15X beam expansion, providing flexibility in the beam expansion scheme. The two beam expanders are supported by a five-dimensional adjustment platform, allowing for adjustment in the X, Y, and Z directions, as well as azimuth and elevation. The diameter of the 193nm laser output from the light source beam expansion system is either 25mm or 15mm.

[0035] After secondary beam expansion, the laser passes through the first 193nm reflector, the second 193nm reflector, and the vertically incident polarizing beam splitter 6. The first 193nm reflector, the second 193nm reflector, the polarizing beam splitter 6, the quarter-wave plate 7, and the third 193nm reflector are supported by a designed enclosed plate. The laser propagates within the enclosed plate. The first 193nm reflector and the second 193nm reflector are fixed within the enclosed plate and can be adjusted for azimuth and pitch.

[0036] S2. The 193nm laser is split using a polarizing beam splitter 6 to obtain a first P-beam and a first S-beam; the first P-beam is transmitted to a quarter-wave plate 7, and the first S-beam is incident into the air for extinction treatment; specifically, extinction treatment is performed using extinction paper; wherein both the polarizing beam splitter 6 and the quarter-wave plate 7 are supported and adjusted by a five-dimensional adjustment stage.

[0037] S3. The polarization angle of the first P-beam is changed by the quarter-wave plate 7 and transmitted to the coupling mirror 9; wherein, after the first P-beam exits from the quarter-wave plate 7, the laser propagation direction is changed by the third 193nm reflector and it is perpendicularly incident on the 193nm coupling mirror 9; wherein, the coupling mirror 9 is fixed to the outside of the closed plate by the adapter fixture and is supported and adjusted by the five-dimensional adjustment table.

[0038] S4. The coupling mirror 9 focuses the 10mm center beam of the incident beam and outputs it to the objective lens 10 under test; at this time, the focus of the coupling mirror 9 and the object-side focus of the objective lens 10 under test are aligned by adjusting the 193nm coupling mirror adjustment fixture.

[0039] S5. The beam passing through the objective lens 10 under test returns along the original path via the ball bearing 11; specifically: after the first P-beam exits from the 193nm objective lens, it enters the ball bearing 11, aligning the focal point of the ball bearing 11 with the image-side focal point of the objective lens 10 under test, thus allowing the 25X expanded laser spot to return along the original path; wherein the objective lens 10 under test is supported and adjusted by a specially designed support structure, and the ball bearing 11 is supported and adjusted by a six-axis adjustment stage; S6. The returned beam passes through the objective lens 10 and is incident on the coupling lens 9; S7. The coupling mirror 9 performs beam reduction on the center 10mm beam of the returning beam and outputs it to the 1 / 4 wave plate 7; S8. Use the quarter-wave plate 7 to convert the polarization angle of the returning beam to obtain the second S-beam; S9. The second S-beam is incident on the polarizing beam splitter 6 and reflected by the polarizing beam splitter 6 to the Shak-Hartmann wavefront sensor 12 for wavefront aberration analysis. The Shak-Hartmann wavefront sensor 12 is housed within a sealed plate and supported and adjusted by a five-dimensional adjustment stage. The emission direction of the second S-beam does not coincide with the emission direction of the first S-beam.

[0040] Furthermore, since the image-side numerical aperture NA of the objective lens 10 under test is 0.552, and the corresponding object-side numerical aperture NA is 0.138, the diameter of the returned beam spot is 14.9 mm. The entrance pupil diameter of the 193 nm coupling lens is 10 mm. After the 14.9 mm diameter beam spot passes through the coupling lens 9, the spot size is reduced to 9.85 mm, which is within the 12 mm receiving aperture of the Shaker-Hartmann wavefront sensor 12. Experimental testing has verified the feasibility of the detection scheme and the stability of the detection system. The central field-of-view aberration of the objective lens 10 under test can be measured to below 10 nm, and the off-axis field-of-view aberration can be measured to below 20 nm.

[0041] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A wavelet aberration detection system for a 193nm objective lens, comprising: The optical system (13) and the support frame (14) are characterized in that the optical system (13) includes a forward optical path and a return optical path; Outbound optical path: It consists of a light source beam expansion system, a self-separating coaxial optical path, a focusing assembly, a test objective (10), and a ball cup (11) connected in sequence; Return optical path: It consists of a ball cup (11), the objective lens under test (10), the beam shrinking assembly, the self-separating coaxial optical path and the Shaker-Hartmann wavefront sensor (12) connected in sequence; The self-separating coaxial optical path is composed of a polarizing beam splitter (6) and a quarter-wave plate (7) connected in sequence; The focusing component and the beam-shrinking component use the same coupling mirror (9); the output beam diameter of the self-separated coaxial optical path is 10 mm larger than the entrance pupil of the coupling mirror (9); The numerical aperture of the coupling mirror (9) is greater than the object-side numerical aperture of the objective lens (10); All devices are adapted for a 193nm wavelength.

2. The wavefront aberration detection system for a 193nm objective lens according to claim 1, characterized in that, The output beam focus of the coupling mirror (9) is aligned with the focus of the objective lens (10) under test.

3. The wavefront aberration detection system for a 193nm objective lens according to claim 2, characterized in that, 1 / 4 wave plate (7) with a diameter of 12.5 mm.

4. A method for wavefront aberration detection of a 193nm objective lens, characterized in that, The wavefront aberration detection system for a 193nm objective lens according to claim 3 includes: S1. Output 193nm laser using a light source beam expander system; S2. The 193nm laser is split using a polarizing beam splitter (6) to obtain the first P beam and the first S beam; the first P beam is transmitted to a quarter-wave plate (7), and the first S beam is incident into the air for extinction. S3. Use a quarter-wave plate (7) to change the polarization angle of the first P beam and transmit it to the coupling mirror (9). S4. The coupling mirror (9) focuses the center 10mm of the incident beam and outputs it to the objective lens (10) under test. S5. The beam of light passing through the objective lens (10) returns via the same path through the spherical cup (11); S6. The returned beam passes through the objective lens (10) and then enters the coupling lens (9). S7. The coupling mirror (9) performs beam reduction on the center 10mm beam of the returning beam and outputs it to the 1 / 4 wave plate (7). S8. Use a quarter-wave plate (7) to convert the polarization angle of the returning beam to obtain the second S-beam; S9. The second S-beam is incident on the polarizing beam splitter (6) and reflected by the polarizing beam splitter (6) to the Shaker-Hartmann wavefront sensor (12) for wavefront aberration analysis.

5. The wavefront aberration detection method for a 193nm objective lens according to claim 4, characterized in that, It also includes multiple mirrors, which are positioned at the input and output ends of the self-separating coaxial optical path.

6. The wavefront aberration detection method for a 193nm objective lens according to claim 4, characterized in that, The diameter of the 193nm laser output by the light source beam expansion system is 25mm or 15mm.

7. The wavefront aberration detection method for a 193nm objective lens according to claim 4, characterized in that, The numerical aperture of the ball cup (11) is 0.9, which is greater than the image-side numerical aperture of the objective lens (10) under test.

8. The wavefront aberration detection method for a 193nm objective lens according to claim 4, characterized in that, The emission direction of the second S-beam does not coincide with the emission direction of the first S-beam.

9. The wavefront aberration detection method for a 193nm objective lens according to claim 5, characterized in that, The optical path between the output end of the light source beam expansion system and the input end of the coupling mirror (9) is fixed inside the enclosed plate.

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