Microscopic object image difference testing method and system based on Shack-Hartmann sensor

Abstract

The invention relates to the technical field of optical detection, and discloses a microscopic objective image difference testing method and system based on a Shack-Hartmann sensor. The system comprises an illumination module, an objective lens module and a detection module. In the method, the illumination module generates a standard point light source divergent spherical wave, and the position of each module is adjusted to enable the modules to be parallel to and coaxial with an objective lens to be measured; driving the objective lens to rotate around the Z axis to a plurality of preset angles through the theta Z turntable, and acquiring a wavefront intensity distribution image by using a Shack-Hartmann wavefront sensor at each angle; performing Zernike polynomial decomposition on the image to obtain wave aberration information and a Zernike coefficient sequence; and then periodic function fitting is carried out on a tilt item and a defocus item, an error aberration item introduced by mechanical runout of the rotary table is separated, and the error aberration item is deducted from measured wave aberration information, so that corrected real wave aberration information is obtained. According to the invention, high-precision, stable and reliable measurement of the image difference of the microscopic object is realized.

Description

Technical Field

[0001] This invention relates to the field of optical detection technology, specifically to a method and system for testing the mirror aberration of microscopic objects based on a Shaker-Hartmann sensor. Background Technology

[0002] In the field of modern optical inspection, the wavefront aberration characteristics of microscope objectives directly determine imaging quality and measurement accuracy. Especially in applications such as photolithography, wafer inspection, and ultra-precision measurement, stringent requirements are placed on controlling the aberrations of microscope objectives. For example, in photolithography systems, if the wavefront aberration of the microscope objective exceeds λ / 50 of the exposure wavelength, it will lead to blurred pattern edges and linewidth deviations, affecting chip yield and performance. In overlay error detection, aberrations introduce spurious pattern displacements, affecting sub-nanometer alignment accuracy. In wafer defect detection, aberrations reduce the contrast between defects and the background, leading to missed or false detections.

[0003] Among existing methods for measuring aberrations in microscopic objectives, the Shackleton-Hartmann wavefront sensor has been widely used due to its advantages such as high measurement speed, large dynamic range, and real-time monitoring. However, when measuring field-dependent aberrations (i.e., aberrations at different axial angles), a high-precision rotary stage is usually required to change the objective lens angle. But the rotary stage inevitably generates radial runout and apical runout during operation. These mechanical errors cause non-ideal displacement of the objective lens optical axis, thus limiting the measurement accuracy. To overcome this problem, existing technologies mostly rely on improving machining and assembly precision to reduce errors, but this approach is not only costly but also fails to fundamentally eliminate the influence of mechanical runout.

[0004] Therefore, in order to solve the problem that existing microscopic object aberration testing methods are significantly affected by mechanical errors and cannot achieve high-precision aberrations, a new technical solution is urgently needed to break through the bottleneck of mechanical precision and improve the accuracy of testing. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a method and system for testing the aberrations of microscope objectives based on a Shaker-Hartmann sensor. During the multi-angle wavefront aberration test of a microscope objective, the method effectively separates and eliminates the error aberrations introduced by the mechanical runout of the rotating stage, thereby obtaining the true wavefront aberration information of the objective and achieving high-precision, stable and reliable aberration measurement.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention discloses a method for testing the aberrations of microscopic objectives based on a Shaker-Hartmann sensor, applicable to a testing system including an illumination module, an objective lens module, and a detection module, comprising the following steps: S1. A standard point light source is generated through the lighting module to emit standard spherical waves; S2. Adjust the position of each module to keep each module and the objective lens under test in the objective lens module parallel to each other and on the same central reference optical axis, so that the focal point of the objective lens under test coincides with the standard point light source. S3. The objective lens under test is rotated around the Z-axis to multiple preset measurement angles through the θZ turntable in the objective lens module. The test is performed at each measurement angle so that the spherical wave carries the wavefront distortion after passing through the objective lens under test and enters the Shaker-Hartmann wavefront sensor in the detection module, thereby obtaining the wavefront intensity distribution image after the distortion of the objective lens under test. S4. Perform Zernike polynomial decomposition on the wavefront intensity distribution image obtained at each measurement angle to obtain wave phase difference information and the corresponding Zernike coefficient sequence; S5. Perform periodic function fitting on the tilt and defocus terms in the Zernike coefficient sequence to separate the error aberration terms introduced by the mechanical runout of the θZ turntable. Subtract the error aberration terms from the measured wave aberration information to obtain the corrected true wave aberration information and wavefront intensity distribution image.

[0007] As a further improvement to the above scheme, in step S4, the Zernike polynomial decomposition formula for the wavefront intensity distribution image acquired at each measurement angle is as follows: ; In the formula, Wavefront intensity distribution images acquired at each measurement angle; x , y The rectangular coordinates of the detection plane of the Shackletmann wavefront sensor; For the first i One measurement angle; , M This represents the number of sampling points; For the first k Individual and The relevant Zernike coefficient, , N This is the sum of the coefficients of the Zernike polynomial decomposition; For the first k Zernike polynomials, , Normalized polar coordinates, , .

[0008] As a further improvement to the above scheme, step S5 includes the following specific steps: S51, From a measurement perspective Related Z The lower-order aberration coefficients are selected from the Ernike coefficient sequence, including: the X-direction tilt term coefficient. Y-direction tilt coefficient and defocusing coefficient Each lower-order aberration coefficient is obtained by linearly superimposing the true aberration coefficient of the objective lens and the error aberration coefficient, expressed by the following formula: ; In the formula, Indicates the lower-order aberration coefficients; Indicates the true aberration coefficient of the objective lens; Indicates the error aberration coefficient; S52. Perform Fourier transform or least squares fitting on each low-order aberration coefficient, and extract the first-order harmonic component as the error aberration term. ; S53, The error aberration term From the measured low-order aberration coefficients Subtract from the middle to obtain the objective lens at the measured angle. The lower-order aberration coefficients after correcting for mechanical errors are as follows: ; S54. Correct the lower-order aberration coefficients With measuring angle Related Z By combining higher-order aberration coefficients from the Ernike coefficient sequence, the measurement angle of the objective lens under test can be reconstructed. The image shows the true wavefront intensity distribution.

[0009] As a further improvement to the above scheme, in step S2, by rotating the θZ turntable and observing the wavefront intensity distribution image of the Shaker-Hartmann wavefront sensor, the three-dimensional position of the standard point light source is adjusted so that the intensity of the points in the wavefront intensity distribution image that do not rotate with the θZ turntable reaches the maximum, thereby completing the alignment of the focal point of the objective lens under test with the standard point light source.

[0010] This invention also discloses a microscopic objective aberration testing system based on a Shaker-Hartmann sensor, applying the testing method described above. The testing system includes an illumination module, an objective lens module, and a detection module. The illumination module includes an LED light source, an optical fiber, an aperture stop, a collimator, a mirror, a standard high-magnification objective lens, a focusing point mask, an XY-axis two-dimensional translation stage, and a Z-axis piezoelectric level shift stage. The light beam emitted by the LED light source is transmitted through the optical fiber to the aperture stop to limit the divergence angle, and then collimated by the collimator. The collimated light beam is refracted by the mirror and then incident on the standard high-magnification objective lens. The standard high-magnification objective lens focuses the light beam at the light-transmitting hole of the focusing point mask, thereby forming a standard point light source. The XY-axis two-dimensional translation stage and the Z-axis piezoelectric level shift stage are used to adjust the three-dimensional position of the standard point light source.

[0011] As a further improvement to the above solution, the objective module includes a test objective, an aberration adjustment assembly, an objective adapter, an XY-axis fine-tuning hinge, and an θZ turntable. The test objective is mounted on the θZ turntable via the objective adapter. The θZ turntable is used to drive the test objective to rotate around the Z-axis to different angles. The aberration adjustment assembly includes multiple independently adjustable micro-motion components for fine-tuning the lens positions inside the test objective to control aberrations. The XY-axis fine-tuning hinge is located between the test objective and the θZ turntable and is used to adjust the horizontal position of the test objective so that the optical axis of the test objective is coaxial with the rotation axis of the θZ turntable. The θZ turntable is mounted on a frame module.

[0012] As a further improvement to the above scheme, the detection module includes a Shakhartmann wavefront sensor, an autocollimator, a five-dimensional adjustment frame, a Shakhartmann adapter, and an autocollimator adapter. The Shakhartmann wavefront sensor is mounted on the five-dimensional adjustment frame and placed above the objective lens under test. The five-dimensional adjustment frame is used to drive the sensor to translate along the X, Y, and Z axes and rotate around the X and Y axes. The autocollimator is used to establish the objective lens measurement reference to ensure the coaxiality and parallelism of the optical path. The Shakhartmann adapter and the autocollimator adapter are used to fix the Shakhartmann wavefront sensor and the autocollimator on a frame module to maintain the stability of the optical path position.

[0013] As a further improvement to the above solution, the testing system also includes a frame module and a Z-axis module; the frame module includes a profile frame, a base plate, and a top plate; wherein, the detection module and the objective lens module are respectively installed on the top and bottom of the top plate, and the top plate has a through hole for accommodating the Shaker-Hartmann wavefront sensor; the Z-axis module is set on the base plate and is used to drive the illumination module to translate along the Z-axis direction to adjust the axial distance between it and the objective lens module.

[0014] As a further improvement to the above solution, the wavelength of the LED light source is adjustable, with a wavelength range of 320nm-1200nm.

[0015] As a further improvement to the above scheme, the size of the focal spot of the standard high-magnification objective lens is 1 to 10 times the size of the aperture of the focal spot mask.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The microscopic objective aberration testing method disclosed in this invention utilizes wavefront data measured by a Shaker-Hartmann sensor to establish a mathematical model and algorithm analysis. This model accurately separates and eliminates spurious aberration signals introduced by the mechanical runout of the rotary stage, obtaining the true aberrations of the objective lens under test at multiple measurement angles. This method overcomes the limitation of traditional testing that heavily relies on pure mechanical precision, achieving a self-correcting closed loop for the system's own mechanical errors. This elevates measurement accuracy to a new level, ensuring the authenticity and reliability of field-dependent aberration test results.

[0017] 2. The microscopic object aberration testing method disclosed in this invention separates the periodic error introduced by mechanical runout through Zernike coefficient harmonic analysis, and achieves sub-micron level aberration correction (accuracy up to λ / 200, λ=632.8nm), breaking through the bottleneck of traditional reliance on mechanical precision.

[0018] 3. The microscopic objective aberration testing system disclosed in this invention can achieve precise adjustment of the distance to the objective lens under test by setting up a Z-axis module; the XY-axis two-dimensional translation stage and Z-axis piezoelectric translation stage of the illumination module can accurately adjust the position of the point light source; the θZ turntable has high positioning accuracy and small end runout and radial runout, ensuring the accuracy of angle adjustment. Through the precise rotation of the θZ turntable, aberration measurement and adjustment of various axial angles of the objective lens under test can be realized, breaking through the limitation of the limited angle measurement range of the existing system, and can comprehensively acquire aberration information at different angles, meeting diverse testing needs.

[0019] 4. The microscopic objective aberration testing system disclosed in this invention uses an illumination module that forms a standard point light source through the sequential action of an LED light source, optical fiber, aperture stop, collimator, and standard high-magnification objective lens. The position of the point light source can be flexibly adjusted by an XY two-dimensional translation stage and a Z-axis piezoelectric level translation stage. The LED light source covers a wide wavelength range of 320nm–1200nm, making it suitable for aberration testing of different types of microscopic objectives in various fields such as biomedical microscopy (visible light), semiconductor detection (deep ultraviolet), and materials science analysis (near-infrared), demonstrating strong versatility.

[0020] 5. This invention introduces an autocollimator into the detection module to establish a reference optical axis, ensuring the coaxiality and parallelism of the optical paths of each module; the five-dimensional adjustment frame can precisely adjust the position of the Shaker-Hartmann wavefront sensor, further improving the detection accuracy and ensuring reliable results. Attached Figure Description

[0021] Figure 1 This is a three-dimensional structural diagram of the microscopic object image aberration testing system based on the Shaker-Hartmann sensor in an embodiment of the present invention.

[0022] Figure 2 for Figure 1 A three-dimensional structural diagram of the central lighting module.

[0023] Figure 3 for Figure 2 A schematic diagram of the structure of the centrally focused spot mask.

[0024] Figure 4 This is a schematic diagram of the optical path principle of the test system in an embodiment of the present invention.

[0025] Figure 5 This is a three-dimensional structural diagram of the objective lens module 4 in an embodiment of the present invention.

[0026] Figure 6 This is a schematic diagram of the wavefront intensity distribution obtained by the Shaker-Hartmann wavefront sensor in an embodiment of the present invention.

[0027] Figure 7 This is a flowchart of a microscopic object image aberration testing method based on a Shaker-Hartmann sensor, as described in an embodiment of the present invention.

[0028] In the diagram: 1. Frame module; 101. Profile frame; 102. Base plate; 103. Top plate; 2. Z-axis module; 201. Wedge-type Z-axis motor; 202. Adapter plate; 3. Lighting module; 301. LED light source; 302. Optical fiber; 303. Aperture stop; 304. Collimator; 305. Mirror; 306. Standard high-magnification objective lens; 307. Focusing spot mask; 3071. Light transmission hole; 308. XY-axis two-dimensional translation stage; 309. Z-axis piezoelectric translation stage; 310. Illumination... 311. Component frame; 312. Mirror adjustment frame; 313. Piezoelectric level shift adapter; 314. Standard objective lens adapter; 315. Mask plate adjustment adapter; 4. Objective lens module; 401. Objective lens under test; 402. Aberration adjustment assembly; 403. Objective lens adapter; 404. XY-axis fine-tuning hinge; 405. θZ turntable; 5. Detection module; 501. Shakhartmann wavefront sensor; 502. Autocollimator; 503. Five-dimensional adjustment frame; 504. Shakhartmann adapter; 505. Autocollimator adapter. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0030] This invention provides a method for testing the mirror aberration of microscopic objects based on a Shaker-Hartmann sensor, which is applied to a microscopic mirror aberration testing system based on a Shaker-Hartmann sensor.

[0031] Please see Figure 1 The testing system may include a frame module 1, a Z-axis module 2, an illumination module 3, an objective lens module 4, and a detection module 5.

[0032] The frame module 1 includes a profile frame 101, a base plate 102, and a top plate 103. The profile frame 101 is made of high-strength aluminum alloy, while the base plate 102 and top plate 103 are made of marble. The high-strength aluminum alloy possesses high rigidity and strength, providing a stable frame support for the system. The marble material has good stability and seismic resistance, effectively reducing the impact of external vibrations on the system. Therefore, it provides a solid installation foundation and highly stable structural support for the test system provided in this embodiment of the invention and its other internal modules.

[0033] The Z-axis module 2 is mounted on the base plate 102 of the frame module 1 and consists of a wedge-type Z-axis motor 201 and its adapter plate 202. Through its precise driving action, it can achieve precise adjustment of the distance between the illumination module 3 and the objective lens module 4. At the same time, the adapter plate 202 provides a stable mounting carrier for the wedge-type Z-axis motor 201, ensuring the high stability support of the Z-axis module 2.

[0034] The detection module 5 is mounted on the top plate 103 of the frame module 1, and includes a Shaker-Hartmann wavefront sensor 501, an autocollimator 502, a five-dimensional adjustment frame 503, a Shaker-Hartmann adapter 504, and an autocollimator adapter 505.

[0035] The Shaker-Hartmann wavefront sensor 501 consists of a microlens array, an imaging detector, and a data processing unit, and in this embodiment, it is responsible for detecting the wavefront aberration of the objective lens. The autocollimator 502 is used to determine the objective lens measurement reference and ensure the consistency of the measurement reference. The five-dimensional adjustment frame 503 can realize translation in the X, Y, and Z directions and rotation adjustment around the X and Y axes, thereby adjusting the Shaker-Hartmann wavefront sensor 501 to the optimal working position and ensuring the accuracy of the results.

[0036] Figure 2 The diagram shows the structure of the lighting module 3, which includes an LED light source 301, an optical fiber 302, an aperture stop 303, a collimator 304, a reflector 305, a standard high-magnification objective lens 306, a focusing point mask 307, an XY-axis two-dimensional translation stage 308, a Z-axis pressure level translation stage 309, a lighting component frame 310, a reflector adjustment bracket 311, a pressure level translation adapter 312, a standard objective lens adapter 313, and a mask adjustment adapter 314.

[0037] The wavelength of the LED light source 301 is adjustable or fixed, ranging from 320 to 1200 nm, which can meet the wavelength requirements of different test scenarios. The specific wavelength is determined according to the system measurement requirements.

[0038] The XY-axis two-dimensional translation stage 308 and the Z-axis pressure level translation stage 309 are used to precisely adjust the position of the point light source to ensure that it accurately coincides with the focal point of the objective lens under test. The pressure level translation adapter 312 provides a stable mounting connection for the translation stage.

[0039] Figure 3 The diagram shows the structure of the focusing light spot mask 307. A light-transmitting hole 3071 is provided at the center of the light-shielding plane of the focusing light spot mask 307. Furthermore, the diameter of the light-transmitting hole 3071 of the focusing light spot mask 307 should be 0.5µm to 2µm, specifically determined according to the system measurement requirements.

[0040] Combination Figures 2 to 4 The light beam emitted by the LED light source 301 is transmitted to the aperture stop 303 via the optical fiber 302, and then collimated by the collimator 304. The collimated light beam is refracted by the mirror 305 and converged by the standard high-magnification objective lens 306 to the light transmission hole 3071 of the focusing point mask plate 307 to form a standard point light source.

[0041] Figure 5 This is a schematic diagram of the objective lens module 4. It is located below the top plate 103 of the frame module and includes the objective lens under test 401, the aberration adjustment component 402, the objective lens adapter 403, the XY fine-tuning hinge 404, and the θZ turntable 405.

[0042] Among them, the objective lens adapter 403 can be adapted to the objective lens 401 with various interfaces, which can meet the testing needs of different testing scenarios. The specific requirements are determined according to the system measurement requirements.

[0043] Furthermore, the aberration adjustment component 402 can independently adjust the position of the lenses constituting the objective lens 401 under test for precise adjustment. It also needs to be compatible with various objective lenses 401 under test, or be individually modified or customized according to the objective lens 401 under test, to meet the testing needs of different testing scenarios, specifically determined according to the system measurement requirements. Further, the aberration adjustment component 402 includes multiple independently adjustable spiral or direct-drive micro-motion components, which can achieve effective aberration control by precisely adjusting the position of the lenses constituting the objective lens under test.

[0044] The XY-axis fine-tuning hinge 404 can make fine adjustments to the position of the objective lens 401 under test, further ensuring the accuracy of the test.

[0045] Furthermore, the positioning accuracy of the θZ turntable 405 is no greater than 2 arcseconds, and the end runout and radial runout are no greater than 0.002mm. Through its precise rotation, aberration measurement and adjustment of various axial angles of the objective lens under test can be accurately realized.

[0046] In this embodiment, a standard point light source is formed at the light-transmitting hole 3071 of the focusing light mask plate 307. The divergent spherical wave emitted by the light source passes through the objective lens 401 under test and carries the distorted wavefront of the objective lens 401 into the Shaker-Hartmann wavefront sensor 501. The Shaker-Hartmann wavefront sensor 501 transmits the detected information to the corresponding host computer. After processing the information, the host computer can obtain the wavefront intensity distribution image after the distortion of the objective lens 401 under test, thus realizing high-precision detection of the wavefront aberration information of the objective lens 401 under test.

[0047] By rotating the objective lens 401 under test using the θZ turntable 405, the wavelet aberration distribution of the objective lens 401 under test at different axial angles is measured and adjusted, such as... Figure 6 As shown, Figure 6 A schematic diagram of the wavefront intensity distribution obtained by the Shaker-Hartmann wavefront sensor. Figure 6 In the diagram, the left and top axes represent the physical positions within the detector's field of view (unit: mm), while the right axis represents the color axes with different intensity values ​​(unit: μm).

[0048] Please see Figure 7 The microscopic objective image aberration testing method based on the Shaker-Hartmann sensor according to embodiments of the present invention includes the following steps: S1. Through the sequential action of the LED light source 301, optical fiber 302, aperture stop 303, collimator 304, reflector 305, standard high-magnification objective lens 306 and focusing spot mask 307 in the lighting module 3, a standard point light source is generated to emit standard spherical waves.

[0049] By turning on the LED light source 301 and setting its operating wavelength, a certain spectral band of light generated by it can be transmitted to the aperture stop 303 via the optical fiber 302 to limit its divergence angle. Then, it is collimated by the collimator 304 to generate a parallel light beam. This is the generation of the primary light source.

[0050] Adjusting the reflector adjustment bracket 311 causes the parallel beam to be refracted in space by the reflector 305, aligning it with the standard high-power objective lens 306. The standard high-power objective lens 306 focuses the refracted collimated beam. Adjusting the axial distance between the focusing light spot mask 307 and the focal point of the standard high-power objective lens 306 ensures that the light-transmitting aperture 3071 of the focusing light spot mask 307 coincides with or covers the focal point of the standard high-power objective lens 306 (the size of the focusing light spot of the standard high-power objective lens 306 should be 1 to 10 times the size of the light-transmitting aperture 3071). This is the generation of the secondary light source, i.e., the standard point light source.

[0051] S2. Adjust the position of each module to keep each module and the objective lens 401 under test in the objective lens module 4 parallel to each other and on the same central reference optical axis, so that the focal point of the objective lens 401 under test coincides with the standard point light source, providing a good optical path basis for subsequent testing.

[0052] The autocollimator 502 is used to confirm that the light-transmitting aperture 3071 of the focusing photomask 307, the mounting surface of the objective lens adapter 403, and the measuring surface of the Shackleton-Hartmann wavefront sensor 501 are parallel. Then, while the θZ turntable 405 rotates, the outer circumference of the objective lens 401 under test is measured using mechanical, electronic, optical, and photoelectric sensors. The XY-axis fine-tuning hinge 404 is adjusted to ensure that the axis of the objective lens 401 coincides with the axis of the θZ turntable 405. It should be noted that by detecting the coaxiality between the outer cylindrical surface of the objective lens and the axis of the turntable, the coincidence of the optical axis and the mechanical axis is indirectly ensured; if there is eccentricity, rotation will cause lateral drift of the optical path.

[0053] By adjusting the XY-axis two-dimensional translation stage 308 and the Z-axis pressure level translation stage 309 in the Z-axis module 2 and the illumination module 3, the focal point of the objective lens 401 under test is precisely aligned with the point light source formed in step S1.

[0054] By rotating the θZ turntable 405 and observing the wavefront distribution image of the Shaker-Hartmann wavefront sensor 501, and then continuously and precisely adjusting the wedge-type Z-axis motor 201, the XY-axis two-dimensional translation stage 308, and the Z-axis piezoelectric level translation stage 309, the intensity of the center point of the wavefront distribution image is maximized, thus completing the precise alignment of the focal point position of the objective lens 401 under test in step three with the point light source formed in step one; at this time, the focused light of the standard high-magnification objective lens 306, the light transmission hole 3071 of the focused light point mask plate, and the focal point of the objective lens 401 under test are all aligned.

[0055] S3. The host computer controls the θZ turntable 405 to rotate the objective lens 401 under test around the Z-axis to multiple preset measurement angles in sequence. The test is performed at each measurement angle so that the spherical wave, after passing through the objective lens 401 under test, carries the wavefront distortion into the Shaker-Hartmann wavefront sensor 501 in the detection module 5, thereby obtaining the image of the distorted wavefront intensity distribution after passing through the objective lens 401 under test.

[0056] S4. Perform Zernike polynomial decomposition on the wavefront intensity distribution image obtained at each measurement angle to obtain wave phase difference information and the corresponding Zernike coefficient sequence.

[0057] In this embodiment, after acquiring the distorted wavefront intensity distribution image of the objective lens 401 under test, the difference between the actual measured spot and the theoretical position in the image is processed to obtain the measured wavefront slope. Then, the wavefront phase is reconstructed based on the Zernike polynomial, and the calculation expression is as follows: ; In the formula, Indicates the wavefront phase; , N This is the sum of the coefficients of the Zernike polynomial decomposition; Zernike coefficient, is The k-th Zernike polynomial; For the first k Zernike polynomials, , Normalized polar coordinates, , .

[0058] Furthermore, the aberrations of the objective lens under test can be quantified based on the reconstructed wavefront distribution. Total wavefront aberration (TotalRMS): excluding translation ( ) and out of focus ( The root mean square value of wavefront distortion following the term: ; In the formula, K Number of valid items (starting from Z5).

[0059] The individual aberration RMS values ​​of the objective lens 401 under test can be extracted based on the reconstructed wavefront distribution to separate aberration components in different directions: Ball difference RMS: ; 0° Astigmatism RMS: ; 45° Astigmatism RMS: ; X-coherence RMS: ; Y coma RMS: .

[0060] The formulas for the RMS values ​​of the aforementioned polynomials are the standard method for wavefront aberration analysis. The coefficients are determined by Zernike theory itself. By comparing the calculated RMS values, the aberration performance of different objectives can be quantitatively determined. The weighting factors (5, 7, 8, 9, etc.) are determined by the orthogonal normalization properties of the Zernike polynomials on the unit circle. These are predefined constants in Zernike theory, primarily used to eliminate the influence of the modulus of each polynomial, ensuring that the calculated RMS values ​​accurately reflect the magnitude of the aberration component and allow for fair comparison between different aberrations.

[0061] By acquiring raw data, reconstructing wavefront slope and wavefront phase using the above methods, and then performing Zernike polynomial fitting and RMS quantization and separation, the repeatability and stability of testing the 401-wavelength aberration of the objective lens under test can be achieved.

[0062] In some embodiments, after obtaining quantified wavefront aberration information, especially by separating aberration components in different directions, the aberration adjustment component 402 can be used to perform sub-micron level online adjustment of the lens in the objective lens 401 under test. This allows for precise intervention in the position of some or all of the lenses in the objective lens 401 under test, in order to improve or eliminate uneven wavefront distribution and achieve high-precision intervention and adjustment of the wavefront aberration information of the objective lens 401 under test.

[0063] In step S4, the Zernike polynomial decomposition formula for the wavefront intensity distribution image acquired at each measurement angle is as follows: ; In the formula, Wavefront intensity distribution images acquired at each measurement angle; x , y The rectangular coordinates of the detection plane of the Shaker-Hartmann wavefront sensor 501; For the first i One measurement angle; , M This represents the number of sampling points; For the first k Individual and The relevant Zernike coefficient.

[0064] S5. Perform periodic function fitting on the tilt and defocus terms in the Zernike coefficient sequence to separate the error aberration terms introduced by the mechanical runout of the θZ turntable 405. Subtract the error aberration terms from the measured wave aberration information to obtain the corrected true wave aberration information and wavefront intensity distribution image.

[0065] Step S5 includes the following specific steps: S51, From a measurement perspective Related Z The lower-order aberration coefficients are selected from the Ernike coefficient sequence, including: the X-direction tilt term coefficient. Y-direction tilt coefficient and defocusing coefficient Each lower-order aberration coefficient is obtained by linearly superimposing the true aberration coefficient of the objective lens and the error aberration coefficient, expressed by the following formula: ; In the formula, Indicates the lower-order aberration coefficients; Indicates the true aberration coefficient of the objective lens; This represents the error aberration coefficient.

[0066] Among them, the radial runout and end face runout The introduced error aberration can be modeled as: ; In the formula, C T and C D This is the sensitivity constant for converting mechanical displacement into Zernike coefficients. This is the phase angle of the mechanical runout error.

[0067] Mechanical runout is due to machining and assembly processes. and Typically varies with the measurement angle It exhibits periodic variations and primarily contains first-order harmonic components. Therefore, this embodiment focuses on the acquired total aberration coefficient sequence. Perform harmonic analysis, specifically step S52.

[0068] S52. Perform Fourier transform or least squares fitting on each low-order aberration coefficient, and extract the first-order harmonic component as the error aberration term. The expression is: ; In the formula, A k , B k The amplitude of the periodic tilt / defocus of the mechanical runout in the X / Y direction factor; C k This is the constant term in the fitting residuals (derived from the assembly and adjustment residual error).

[0069] S53, The error aberration term From the measured low-order aberration coefficients Subtracting from the middle, we obtain the measurement angle of the objective lens 401 under test. The lower-order aberration coefficients after correcting for mechanical errors are as follows: ; S54. Correct the lower-order aberration coefficients With measuring angle Related Z By combining the higher-order aberration coefficients in the Ernike coefficient sequence (higher-order aberrations are negligible due to minute mechanical runout), the measurement angle of the objective lens 401 under test can be reconstructed. The image shows the true wavefront intensity distribution.

[0070] In some embodiments, after the test is completed, the operator can use the aberration adjustment component 402 to precisely adjust the objective lens 401 under test based on this high-precision wavefront information until the wavefront aberration at all angles meets the design requirements.

[0071] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for measuring mirror aberration of microscopic objects based on a Shaker-Hartmann sensor, characterized in that, The method applied to a testing system including an illumination module (3), an objective lens module (4), and an inspection module (5) includes the following steps: S1. A standard point light source is generated through the lighting module (3) to emit standard spherical waves; S2. Adjust the position of each module to keep each module and the objective lens (401) in the objective lens module (4) parallel to each other and on the same central reference optical axis, so that the focal point of the objective lens (401) coincides with the standard point light source; S3. The objective lens (401) under test is rotated around the Z-axis to multiple preset measurement angles by the θZ turntable (405) in the objective lens module (4). The test is performed at each measurement angle so that the spherical wave carries the wavefront distortion after passing through the objective lens (401) under test and enters the Shaker-Hartmann wavefront sensor (501) in the detection module (5) to obtain the wavefront intensity distribution image after the distortion of the objective lens (401) under test. S4. Perform Zernike polynomial decomposition on the wavefront intensity distribution image obtained at each measurement angle to obtain wave phase difference information and the corresponding Zernike coefficient sequence; S5. Perform periodic function fitting on the tilt and defocus terms in the Zernike coefficient sequence to separate the error aberration terms introduced by the mechanical runout of the θZ turntable (405). Subtract the error aberration terms from the measured wave aberration information to obtain the corrected true wave aberration information and wavefront intensity distribution image.

2. The method for testing mirror aberrations of microscopic objects based on a Shaker-Hartmann sensor according to claim 1, characterized in that, In step S4, the Zernike polynomial decomposition formula for the wavefront intensity distribution image acquired at each measurement angle is as follows: In the formula, Wavefront intensity distribution images acquired at each measurement angle; x , y Cartesian coordinates of the plane detected by the Shaker-Hartmann wavefront sensor (501); For the first i One measurement angle; , M This represents the number of sampling points; For the first k Individual and The relevant Zernike coefficient, , N This is the sum of the coefficients of the Zernike polynomial decomposition; For the first k Zernike polynomials, , Normalized polar coordinates, , .

3. The method for testing mirror aberrations of microscopic objects based on a Shaker-Hartmann sensor according to claim 2, characterized in that, Step S5 includes the following specific steps: S51, From a measurement perspective Related Z The lower-order aberration coefficients are selected from the Ernike coefficient sequence, including: the X-direction tilt term coefficient. Y-direction tilt coefficient and defocusing coefficient Each lower-order aberration coefficient is obtained by linearly superimposing the true aberration coefficient of the objective lens and the error aberration coefficient, expressed by the following formula: In the formula, Indicates the lower-order aberration coefficients; Indicates the true aberration coefficient of the objective lens; Indicates the error aberration coefficient; S52. Perform Fourier transform or least squares fitting on each low-order aberration coefficient, and extract the first-order harmonic component as the error aberration term. ; S53, The error aberration term From the measured low-order aberration coefficients Subtracting from the middle, we obtain the measurement angle of the objective lens (401) under test. The lower-order aberration coefficients after correcting for mechanical errors are as follows: S54. Correct the lower-order aberration coefficients With measuring angle Related Z By combining higher-order aberration coefficients from the Ernike coefficient sequence, the measurement angle of the objective lens (401) under test can be reconstructed. The image shows the true wavefront intensity distribution.

4. The method for testing mirror aberrations of microscopic objects based on a Shaker-Hartmann sensor according to claim 1, characterized in that, In step S2, by rotating the θZ turntable (405) and observing the wavefront intensity distribution image of the Shaker-Hartmann wavefront sensor (501), the three-dimensional position of the standard point light source is adjusted so that the intensity of the point in the wavefront intensity distribution image that does not rotate with the θZ turntable (405) reaches the maximum, thereby completing the alignment of the focal point of the objective lens (401) under test with the standard point light source.

5. A microscopic objective image aberration testing system based on a Shaker-Hartmann sensor, characterized in that, The test system is a test system comprising an illumination module (3), an objective lens module (4), and a detection module (5) as described in any one of claims 1 to 4; wherein the illumination module (3) comprises an LED light source (301), an optical fiber (302), an aperture stop (303), a collimator (304), a mirror (305), a standard high-magnification objective lens (306), a focusing spot mask (307), an XY-axis two-dimensional translation stage (308), and a Z-axis piezoelectric translation stage (309); the LED light source (301) comprises an LED light source (302), an optical fiber (302), an aperture stop (303), a collimator (304), a mirror (305), a standard high-magnification objective lens (306), a focusing spot mask (307), an XY-axis two-dimensional translation stage (308), and a Z-axis piezoelectric translation stage (309); the LED light source (302) comprises an LED light source (303) and a detection module (5). 1) The emitted beam is transmitted to the aperture stop (303) via the optical fiber (302) to limit the divergence angle, and then collimated by the collimator (304). After collimation, the beam is refracted by the mirror (305) and then incident on the standard high-power objective lens (306). The standard high-power objective lens (306) focuses the beam at the light-transmitting hole (3071) of the focusing point mask plate (307), thereby forming a standard point source. The XY-axis two-dimensional translation stage (308) and the Z-axis piezoelectric level translation stage (309) are used to adjust the three-dimensional position of the standard point source, respectively.

6. The microscopic objective image aberration testing system based on the Shaker-Hartmann sensor according to claim 5, characterized in that, The objective module (4) includes an objective lens under test (401), an aberration adjustment assembly (402), an objective lens adapter (403), an XY-axis fine-tuning hinge (404), and an θZ turntable (405). The objective lens under test (401) is mounted on the θZ turntable (405) via the objective lens adapter (403). The θZ turntable (405) is used to drive the objective lens under test (401) to rotate around the Z-axis to different angles. The aberration adjustment assembly (402) includes multiple An independently adjustable micro-motion component is used to fine-tune the position of the lens inside the objective lens (401) to control aberrations; an XY-axis fine-tuning hinge (404) is set between the objective lens (401) and the θZ turntable (405) to adjust the horizontal position of the objective lens (401) so that the optical axis of the objective lens (401) and the rotation axis of the θZ turntable (405) remain coaxial; the θZ turntable (405) is mounted on a frame module (1).

7. The microscopic objective image aberration testing system based on the Shaker-Hartmann sensor according to claim 5, characterized in that, The detection module (5) includes a Shaker-Hartmann wavefront sensor (501), an autocollimator (502), a five-dimensional adjustment frame (503), a Shaker-Hartmann adapter (504), and an autocollimator adapter (505). The Shaker-Hartmann wavefront sensor (501) is mounted on the five-dimensional adjustment frame (503) and placed above the objective lens (401) to be tested. The five-dimensional adjustment frame (503) is used to drive the sensor to translate along the X, Y, and Z axes and rotate around the X and Y axes. The autocollimator (502) is used to establish the objective lens measurement reference to ensure the coaxiality and parallelism of the optical path. The Shaker-Hartmann adapter (504) and the autocollimator adapter (505) are used to fix the Shaker-Hartmann wavefront sensor (501) and the autocollimator (502) on a frame module (1) to keep the optical path position stable.

8. The microscopic objective image aberration testing system based on the Shaker-Hartmann sensor according to claim 5, characterized in that, The testing system also includes a frame module and a Z-axis module (2); the frame module includes a profile frame (101), a base plate (102) and a top plate (103); wherein, the detection module (5) and the objective lens module (4) are respectively installed on the top and bottom of the top plate (103), and the top plate (103) is provided with a through hole for accommodating the Shaker-Hartmann wavefront sensor (501); the Z-axis module (2) is set on the base plate (102) and is used to drive the illumination module (3) to translate along the Z-axis direction to adjust the axial distance between it and the objective lens module (4).

9. The microscopic objective image aberration testing system based on the Shaker-Hartmann sensor according to claim 5, characterized in that, The wavelength of the LED light source (301) is adjustable, with a wavelength range of 320nm-1200nm.

10. The microscopic objective image aberration testing system based on the Shaker-Hartmann sensor according to claim 5, characterized in that, The size of the focal spot of the standard high-power objective lens (306) is 1 to 10 times the size of the aperture (3071) of the focal spot mask (307).

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