Microscope objective aberration testing method and system based on shack-hartmann sensor

Abstract

The present application relates to the field of optical detection technology, disclose a microscopic objective aberration testing method and system based on Shack-Hartmann sensor. System includes illumination module, objective module and detection module. In the method, the illumination module generates standard point light source divergent spherical wave, and adjusts the position of each module to make it parallel and coaxial with the objective lens to be measured; through the θZ turntable drives the objective lens to rotate around the Z axis to a plurality of preset angles, the wavefront intensity distribution image is obtained by using the Shack-Hartmann wavefront sensor at each angle; the image is decomposed by Zernike polynomial, and the wave aberration information and Zernike coefficient sequence are obtained; then the tilt term and the defocus term are fitted by periodic function, the error aberration term introduced by the turntable mechanical jump is separated, and it is deducted from the measured wave aberration information, so as to obtain the corrected real wave aberration information. The present application realizes the high precision, stable and reliable measurement of microscopic objective aberration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical detection technology, in particular to a microscopic objective aberration testing method and system based on a Shack-Hartmann sensor. BACKGROUND

[0002] In the field of modern optical detection, the wave aberration characteristics of a microscopic objective directly determine the imaging quality and measurement accuracy. Especially in application scenarios such as photolithography, wafer detection, and ultra-precision measurement, stringent requirements are placed on the control of the wave aberration of the microscopic objective. For example, in a photolithography system, if the wave aberration of the microscopic objective exceeds λ / 50 of the exposure wavelength, it will cause pattern edge blurring and line width deviation, affecting the chip yield and performance; in overlay error detection, aberration will introduce false pattern displacement, affecting sub-nanometer alignment accuracy; in wafer defect detection, aberration will reduce the contrast between defects and the background, resulting in missed detection or false detection.

[0003] In existing microscopic objective aberration testing methods, a Shack-Hartmann wavefront sensor has been widely used due to its fast measurement speed, large dynamic range, and real-time monitoring capabilities. However, when measuring field-dependent aberration (i.e., aberration at different angles along the optical axis), a high-precision rotary stage is usually required to change the objective angle. However, the rotary stage inevitably produces radial runout and end face runout during operation, and these mechanical errors will cause non-ideal displacement of the optical axis of the objective, thereby limiting the testing accuracy. To overcome this problem, existing technologies often rely on improving the machining and assembly precision to reduce errors, but this approach not only has high costs, but also cannot fundamentally eliminate the influence of mechanical runout.

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

[0005] To solve the technical problems existing in the prior art, the present application provides a microscopic objective aberration testing method and system based on a Shack-Hartmann sensor, which effectively separates and eliminates the error aberration introduced by the mechanical runout of the rotary stage during multi-angle wave aberration testing of the microscopic objective, thereby obtaining the true wave aberration information of the objective and achieving high-precision, stable, and reliable aberration measurement.

[0006] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0007] The present application discloses a microscopic objective aberration testing method based on a Shack-Hartmann sensor, which is applied to a testing system including an illumination module, an objective module, and a detection module, and includes the following steps:

[0008] S1, generating a standard point light source by the illumination module to emit a standard spherical wave;

[0009] S2, adjusting the position of each module to keep each module and the to-be-tested objective lens in the objective lens module in a parallel state and on a same central reference optical axis, so that the focal point of the to-be-tested objective lens coincides with the standard point light source;

[0010] S3, rotating the to-be-tested objective lens around the Z axis to a plurality of preset measurement angles by the θZ turntable in the objective lens module, testing at each measurement angle, so that the spherical wave carrying wavefront distortion after the to-be-tested objective lens enters the Shack-Hartmann wavefront sensor in the detection module, thereby obtaining a wavefront intensity distribution image distorted by the to-be-tested objective lens;

[0011] S4, performing Zernike polynomial decomposition on the wavefront intensity distribution image obtained at each measurement angle to obtain wavefront difference information and a corresponding Zernike coefficient sequence;

[0012] S5, performing periodic function fitting on the tilt term and the defocus term in the Zernike coefficient sequence to separate error aberration terms introduced by mechanical jitter of the θZ turntable, subtracting the error aberration terms from the measured wave aberration information to obtain corrected real wave aberration information and a wavefront intensity distribution image.

[0013] As a further improvement of the above scheme, in step S4, the expression formula for performing Zernike polynomial decomposition on the wavefront intensity distribution image obtained at each measurement angle is:

[0014] ;

[0015] In the formula, is the wavefront intensity distribution image obtained at each measurement angle; x 、 y is the rectangular coordinates of the detection plane of the Shack-Hartmann wavefront sensor; is the i measurement angle; , M is the number of sampling points; is the k Zernike coefficient related to the measurement angle, , N is the coefficient sum of the Zernike polynomial decomposition; is the k Zernike polynomial, 、 is the normalized polar coordinate, , .

[0016] As a further improvement to the above scheme, step S5 includes the following specific steps:

[0017] 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:

[0018] ;

[0019] In the formula, Indicates the lower-order aberration coefficients; Indicates the true aberration coefficient of the objective lens; Indicates the error aberration coefficient;

[0020] 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. ;

[0021] 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:

[0022] ;

[0023] 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.

[0024] 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.

[0025] The application further discloses a microscopic objective aberration testing system based on a Shack-Hartmann sensor, which applies the testing method; the testing system comprises an illumination module, an objective module and a detection module; the illumination module comprises an LED light source, an optical fiber, an aperture diaphragm, a collimator, a mirror, a standard high-power objective, a focused light point mask plate, an XY two-dimensional translation stage and a Z piezoelectric translation stage; the light beam emitted by the LED light source is transmitted to the aperture diaphragm through the optical fiber to limit the divergence angle, and then is collimated by the collimator; the collimated light beam is reflected by the mirror and then is incident on the standard high-power objective; the standard high-power objective focuses the light beam on the light transmission hole of the focused light point mask plate, so that a standard point light source is formed; the XY two-dimensional translation stage and the Z piezoelectric translation stage are respectively used for adjusting the three-dimensional position of the standard point light source.

[0026] As a further improvement of the above-mentioned scheme, the objective module comprises a to-be-tested objective, an aberration adjustment assembly, an objective adapter, an XY fine adjustment hinge and a theta Z turntable; the to-be-tested objective is installed on the theta Z turntable through the objective adapter; the theta Z turntable is used for driving the to-be-tested objective to rotate around the Z axis direction to different angles; the aberration adjustment assembly comprises a plurality of independently adjustable micro-motion components, which are used for fine adjustment of the lens position inside the to-be-tested objective to control the aberration; the XY fine adjustment hinge is arranged between the to-be-tested objective and the theta Z turntable, and is used for adjusting the horizontal position of the to-be-tested objective, so that the optical axis of the to-be-tested objective is coaxial with the rotation axis of the theta Z turntable; the theta Z turntable is installed on a frame module.

[0027] As a further improvement of the above-mentioned scheme, the detection module comprises a Shack-Hartmann wavefront sensor, a collimator, a five-dimensional adjustment frame, a Shack-Hartmann adapter and a collimator adapter; the Shack-Hartmann wavefront sensor is installed on the five-dimensional adjustment frame and is placed above the to-be-tested objective; the five-dimensional adjustment frame is used for driving the sensor to translate along the X, Y and Z axes and rotate around the X and Y axes; the collimator is used for establishing an objective measurement reference to ensure the coaxiality and parallelism of the optical path; the Shack-Hartmann adapter and the collimator adapter are respectively used for fixing the Shack-Hartmann wavefront sensor and the collimator on a frame module to keep the position of the optical path stable.

[0028] As a further improvement of the above-mentioned scheme, the testing system further comprises a frame module and a Z module; the frame module comprises a profile frame, a bottom plate and a top plate; the detection module and the objective module are respectively installed on the top and bottom of the top plate, and a through hole for accommodating the Shack-Hartmann wavefront sensor is formed in the top plate; the Z module is arranged on the bottom plate and is used for driving the illumination module to translate along the Z axis direction to adjust the axial distance between the illumination module and the objective module.

[0029] As a further improvement of the above-mentioned scheme, the wavelength of the LED light source is adjustable, and the wavelength range is 320nm-1200nm.

[0030] As a further improvement of the above scheme, the focusing spot size of the standard high-power objective lens is 1-10 times the size of the light transmission hole of the focusing spot mask plate.

[0031] Compared with the prior art, the present application has the following advantages:

[0032] 1. The microscopic objective lens aberration testing method disclosed in the present application, by using the wavefront data measured by the Shack-Hartmann sensor, establishes a mathematical model and algorithm analysis, accurately separates and eliminates the false aberration signal introduced by the mechanical runout of the rotating table, and obtains the real aberration of the objective lens to be tested at multiple measurement angles. This method breaks through the limitation of traditional testing which relies heavily on pure mechanical precision, realizes self-correction closed loop of the system's own mechanical error, improves the measurement accuracy to a new level, and ensures the authenticity and reliability of the field-dependent aberration test results.

[0033] 2. The microscopic objective lens aberration testing method disclosed in the present application, by Zernike coefficient harmonic analysis, separates the periodic error introduced by mechanical runout, realizes sub-micron level aberration correction (accuracy up to λ / 200, λ=632.8nm), and breaks through the bottleneck of traditional mechanical precision dependence.

[0034] 3. The microscopic objective lens aberration testing system disclosed in the present application, by setting the Z direction module, precise adjustment of the distance from the objective lens to be tested can be realized; the XY two-dimensional translation stage and the Z direction piezoelectric translation stage of the illumination module can accurately adjust the position of the point light source; the θZ rotary table has high positioning accuracy, small end runout and radial runout, which ensures the accuracy of angle adjustment; through the precise rotation of the θZ rotary table, aberration measurement and adjustment of each angle in the axial direction of the objective lens to be tested can be realized, which breaks through the limitation of the limited angle measurement range of the existing system, can comprehensively obtain aberration information at different angles, and meets the diversified testing needs.

[0035] 4. The microscopic objective lens aberration testing system disclosed in the present application, the illumination module forms a standard point light source through LED light source, optical fiber, aperture diaphragm, collimator and standard high-power objective lens in stages, and the position of the point light source can be flexibly adjusted by the XY two-dimensional translation stage and the Z direction piezoelectric translation stage. The LED light source covers a wide wavelength range of 320nm-1200nm, and is suitable for aberration testing of different types of microscopic objective lenses in various fields such as biomedical microscopic imaging (visible light), semiconductor detection (deep ultraviolet), material science analysis (near infrared), etc., and has strong universality.

[0036] 5. The present application introduces a collimator in the detection module to establish a reference optical axis and ensure the coaxiality and parallelism of the light paths of each module; the five-dimensional adjustment frame can accurately adjust the position of the Shack-Hartmann wavefront sensor, further improve the detection accuracy, and ensure the reliability of the results. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1The figure is a schematic diagram of the three-dimensional structure of the microscopic objective aberration testing system based on the Shack-Hartmann sensor in the embodiment of the present application.

[0038] Figure 2 The figure is a schematic diagram of the three-dimensional structure of the illumination module. Figure 1

[0039] Figure 3 The figure is a schematic diagram of the three-dimensional structure of the objective module 4 in the embodiment of the present application. Figure 2

[0040] Figure 4 The figure is a schematic diagram of the optical path principle of the testing system in the embodiment of the present application.

[0041] Figure 5 The figure is a schematic diagram of the three-dimensional structure of the objective module 4 in the embodiment of the present application.

[0042] Figure 6 The figure is a schematic diagram of the wavefront intensity distribution obtained by the Shack-Hartmann wavefront sensor in the embodiment of the present application.

[0043] Figure 7 The figure is a flow chart of the microscopic objective aberration testing method based on the Shack-Hartmann sensor in the embodiment of the present application.

[0044] In the figure: 1, frame module; 101, profile frame; 102, bottom plate; 103, top plate; 2, Z-direction module; 201, wedge block type Z-direction motor; 202, adapter plate; 3, illumination module; 301, LED light source; 302, optical fiber; 303, aperture diaphragm; 304, collimator; 305, reflector; 306, standard high-power objective lens; 307, focused light point mask plate; 3071, light transmission hole; 308, XY-direction two-dimensional translation stage; 309, Z-direction piezoelectric translation stage; 310, illumination assembly frame; 311, reflector adjusting frame; 312, piezoelectric translation adapter; 313, standard objective lens adapter; 314, mask plate adjusting adapter; 4, objective module; 401, objective to be tested; 402, aberration adjusting assembly; 403, objective lens adapter; 404, XY-direction fine adjustment hinge; 405, θZ turntable; 5, detection module; 501, Shack-Hartmann wavefront sensor; 502, autocollimator; 503, five-dimensional adjusting frame; 504, Shack-Hartmann adapter; 505, autocollimator adapter. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. ​​

[0046] The embodiment of the present application provides a microscopic objective aberration testing method based on a Shack-Hartmann sensor, which is applied to a microscopic objective aberration testing system based on a Shack-Hartmann sensor.

[0047] Please refer to Figure 1 The testing system can include a frame module 1, a Z-direction module 2, an illumination module 3, an objective lens module 4 and a detection module 5.

[0048] The frame module 1 includes a profile frame 101, a bottom plate 102 and a top plate 103, wherein the profile frame 101 is made of high-strength aluminum alloy, and the bottom plate 102 and the top plate 103 are made of marble. The high-strength aluminum alloy has high rigidity and strength, and can provide stable frame support for the system; the marble material has good stability and shock resistance, which can effectively reduce the influence of external vibration on the system, thereby providing a solid installation foundation and high-stability structural support for the testing system and the remaining modules contained therein.

[0049] The Z-direction module 2 is arranged on the bottom plate 102 of the frame module 1 and is composed of a wedge block type Z-direction motor 201 and an adapter plate 202 thereof. Through the precise driving action, the distance between the illumination module 3 and the objective lens module 4 can be accurately adjusted, and at the same time, the adapter plate 202 provides a stable installation carrier for the wedge block type Z-direction motor 201, ensuring the high-stability support of the Z-direction module 2.

[0050] The detection module 5 is arranged on the top plate 103 of the frame module 1 and includes a Shack-Hartmann wavefront sensor 501, a collimator 502, a five-dimensional adjustment frame 503, a Shack-Hartmann adapter 504 and a collimator adapter 505.

[0051] The Shack-Hartmann wavefront sensor 501 is composed of a microlens array, an imaging detector and a data processing unit, and is responsible for detecting the objective lens wavefront aberration in the embodiment; the collimator 502 is used to determine the objective lens measurement reference, ensuring the consistency of the measurement reference; the five-dimensional adjustment frame 503 can realize the translation in X, Y and Z directions and the rotation adjustment around X and Y axes, so as to adjust the Shack-Hartmann wavefront sensor 501 to the best working position and ensure the accuracy of the results.

[0052] Figure 2 The structure of the illumination module 3 is shown in the structural schematic view, and the components thereof include an LED light source 301, an optical fiber 302, an aperture diaphragm 303, a collimator 304, a reflector 305, a standard high-power objective lens 306, a focused light point mask plate 307, an XY two-dimensional translation stage 308, a Z-direction piezoelectric translation stage 309, an illumination assembly frame 310, a reflector adjustment frame 311, a piezoelectric translation adapter 312, a standard objective lens adapter 313 and a mask plate adjustment adapter 314.

[0053] The wavelength of the LED light source 301 can be adjusted or fixed, ranging from 320-1200nm, to meet the requirements of different test scenarios for light source wavelength, depending on the system measurement requirements.

[0054] The XY two-dimensional translation stage 308 and the Z-direction piezoelectric translation stage 309 are used to accurately adjust the position of the point light source, ensuring that it accurately coincides with the focusing point of the objective lens to be tested, and the piezoelectric translation adapter 312 provides a stable mounting connection for the translation stage.

[0055] Figure 3 The structure diagram of the focusing light point mask plate 307 is shown, and a light transmission hole 3071 is provided in the center of the light shielding plane of the focusing light point mask plate 307. Further, the diameter of the light transmission hole 3071 of the focusing light point mask plate 307 should be 0.5um~2um, and the specific value is determined according to the system measurement requirements.

[0056] In combination Figures 2 to 4 , the LED light source 301 emits a light beam that is transmitted to the aperture diaphragm 303 through the optical fiber 302, and then collimated by the collimator 304. The collimated light beam is reflected by the reflector 305 and is converged by the standard high-power objective lens 306 to the light transmission hole 3071 of the focusing light point mask plate 307, forming a standard point light source.

[0057] Figure 5 The structure diagram of the objective lens module 4 is shown. It is arranged below the top plate 103 of the frame module, and includes the objective lens to be tested 401, the aberration adjustment assembly 402, the objective lens adapter 403, the XY fine adjustment hinge 404, and the θZ turntable 405.

[0058] The objective lens adapter 403 can adapt to various interfaces of the objective lens to be tested 401, and can meet the testing requirements of different test scenarios, depending on the system measurement requirements.

[0059] In addition, the aberration adjustment assembly 402 can independently adjust the position of the lens that constitutes the objective lens to be tested 401 for precise adjustment. It also needs to adapt to multiple objective lenses to be tested 401, or be individually changed or customized according to the objective lens to be tested 401, to meet the testing requirements of different test scenarios, depending on the system measurement requirements. Further, the aberration adjustment assembly 402 includes multiple independently adjustable screw or direct-drive micro-motion components, which can effectively control the aberration by precisely adjusting the position of the lens that constitutes the objective lens to be tested.

[0060] The XY fine adjustment hinge 404 can finely adjust the position of the objective lens to be tested 401, further ensuring the accuracy of the test.

[0061] Further, the positioning accuracy of the theta Z turntable 405 is not greater than 2 angular seconds, the end jump and the radial jump are not greater than 0.002 mm, and through the accurate rotation, the axial aberration measurement and adjustment of the to-be-measured objective lens at each angle can be accurately realized.

[0062] In the embodiment, the standard point light source is formed at the light transmission hole 3071 of the focusing light point mask plate 307, and the divergent spherical wave carries the wavefront distorted by the to-be-measured objective lens 401 into the Shack-Hartmann wavefront sensor 501 after passing through the to-be-measured objective lens 401. The Shack-Hartmann wavefront sensor 501 transmits the detected information to the matched host computer, and the host computer can obtain the wavefront intensity distribution image distorted by the to-be-measured objective lens 401 after processing the information, that is, the high-precision detection of the wave aberration information of the to-be-measured objective lens 401 is realized.

[0063] The angle of the to-be-measured objective lens 401 is rotated through the theta Z turntable 405, and the wave aberration distribution of the to-be-measured objective lens 401 under different angles is measured and adjusted. Figure 6 Figure 6 It is a wavefront intensity distribution diagram obtained by the Shack-Hartmann wavefront sensor. Figure 6 In the figure, the coordinate axes on the left and the top represent the physical positions (unit: mm) in the field of view of the detector, and the color axis on the right represents different intensity values (unit: μm).

[0064] Referring to Figure 7 The microscopic objective lens aberration testing method based on the Shack-Hartmann sensor of the embodiment of the application includes the following steps:

[0065] S1, the standard point light source is generated to diverge the standard spherical wave through the LED light source 301, the optical fiber 302, the aperture diaphragm 303, the collimator 304, the reflector 305, the standard high-power objective lens 306 and the focusing light point mask plate 307 in the illumination module 3 in sequence.

[0066] By turning on the LED light source 301 and setting the working wavelength, the light beam of a certain spectrum generated by the LED light source 301 can be transmitted to the aperture diaphragm 303 through the optical fiber 302 to limit the divergence angle, and then collimated through the collimator 304 to generate a parallel light beam. Here, it is the generation of a light source.

[0067] ​Adjusting the mirror adjusting frame 311 so that the parallel light beam is reflected by the mirror 305 in space to align with the incident standard high-power objective 306, the standard high-power objective 306 focuses the reflected collimated light beam, and the axial distance between the focusing light point mask plate 307 and the focusing point of the standard high-power objective 306 is adjusted so that the light transmission hole 3071 of the focusing light point mask plate 307 coincides with or is covered by the focusing point of the standard high-power objective 306 (the size of the focusing point of the standard high-power objective 306 should be 1-10 times the size of the light transmission hole 3071), and the secondary light source, i.e., the standard point light source, is generated.

[0068] S2, adjusting the position of each module to keep each module and the to-be-tested objective 401 in the objective module 4 in a parallel state and on the same central reference optical axis, so that the focusing point of the to-be-tested objective 401 coincides with the standard point light source, providing a good optical path basis for subsequent testing.

[0069] The light transmission hole 3071 of the focusing photo mask plate 307, the mounting surface of the objective adapter 403, and the measurement surface of the Shack-Hartmann wavefront sensor 501 are confirmed to be parallel by using the autocollimator 502; then the outer circumferential surface of the to-be-tested objective 401 is measured by mechanical, electronic, optical, and photoelectric sensors while the θZ rotary table 405 is rotating, and the to-be-tested objective 401 axis is adjusted to coincide with the θZ rotary table 405 axis by adjusting the XY fine adjustment hinge 404. It should be noted that the coaxiality of the objective outer cylindrical surface and the rotary table axis is detected to indirectly ensure that the optical axis coincides with the mechanical axis; if there is eccentricity, the optical path will drift laterally when rotating.

[0070] The XY two-dimensional translation stage 308 and the Z piezoelectric translation stage 309 in the Z module 2 and the illumination module 3 are adjusted to make the focusing point position of the to-be-tested objective 401 coincide with the point light source formed in step S1.

[0071] The θZ rotary table 405 is rotated, and the wavefront distribution image of the Shack-Hartmann wavefront sensor 501 is observed, and then the wedge Z motor 201, the XY two-dimensional translation stage 308, and the Z piezoelectric translation stage 309 are continuously and accurately adjusted to make the center point intensity of the wavefront distribution image maximum, i.e., the focusing point position of the to-be-tested objective 401 coincides with the point light source formed in step one, and the standard high-power objective 306 focusing light, the light transmission hole 3071 of the focusing light point mask plate, and the focusing point of the to-be-tested objective 401 coincide.

[0072] S3, rotate the objective lens 401 around the Z axis to a plurality of preset measurement angles in sequence by the host computer control θZ rotary table 405, test at each measurement angle, so that the spherical wave carrying wavefront aberration after the objective lens 401 enters the Shack-Hartmann wavefront sensor 501 in the detection module 5, thereby obtaining the aberration wavefront intensity distribution image through the objective lens 401.

[0073] S4, the wavefront intensity distribution image obtained at each measurement angle is decomposed by Zernike polynomial to obtain wavefront aberration information and corresponding Zernike coefficient sequence.

[0074] In this embodiment, after obtaining the aberration wavefront intensity distribution image carrying the objective lens 401, the shift difference between the actual measurement spot and the theoretical position in the image is processed to obtain the measurement wavefront slope, and then the wavefront phase is reconstructed based on the Zernike polynomial, and the expression is:

[0075] ;

[0076] In the formula, represents the wavefront phase; , N is the sum of the coefficients of the Zernike polynomial decomposition; is the Zernike coefficient, and is the kth Zernike polynomial; is the first k Zernike polynomial, , is the normalized polar coordinate, , .

[0077] Further, the aberration of the objective lens 401 can be quantified according to the reconstructed wavefront distribution, and the total wave aberration (TotalRMS) is the root mean square value of the wavefront aberration after excluding the translation (T) and defocus (D) terms:

[0078] ;

[0079] In the formula, K is the effective term number (Z5).

[0080] The single aberration RMS value of the objective lens 401 can be stripped according to the reconstructed wavefront distribution to separate the aberration components in different directions:

[0081] Spherical aberration RMS: ;

[0082] 0° astigmatism RMS: ;​​

[0083] 45° astigmatism RMS: ;

[0084] X coma RMS: ;

[0085] Y coma RMS: .

[0086] The formula of the above multiple aberration RMS values is a standard method for wavefront aberration analysis. The coefficient sequence number is determined by the Zernike theory itself, and the advantages and disadvantages of different objective lenses can be quantitatively judged by comparing the calculated RMS values. The weight factor (5, 7, 8, 9, etc.) is determined by the orthogonal normalization characteristics of Zernike polynomials on a unit circle, and is a constant defined in advance in Zernike theory. It is mainly used to eliminate the influence of the modulus of each polynomial itself, so that the calculated RMS value truly reflects the size of the aberration component, and different aberrations can be compared fairly.

[0087] After the original data is collected, the wavefront slope and the wavefront phase are reconstructed, and then the Zernike polynomial fitting and the RMS quantization and separation are performed, the test repeatability and stability of the wave aberration of the measured objective lens 401 can be realized.

[0088] In some embodiments, after obtaining the quantized wave aberration information, especially separating the aberration components in different directions, the sub-micron online adjustment of the lens level in the measured objective lens 401 can be performed with the aid of the aberration adjustment assembly 402, so as to finely intervene in the position of part or all of the lenses in the measured objective lens 401, so as to improve or eliminate the uneven wavefront distribution, and realize high-precision intervention adjustment of the wave aberration information of the measured objective lens 401.

[0089] In step S4, the expression formula for Zernike polynomial decomposition of the wavefront intensity distribution image obtained at each measurement angle is:

[0090] ;

[0091] In the formula, is the wavefront intensity distribution image obtained at each measurement angle; x , y is the rectangular coordinate of the Shack-Hartmann wavefront sensor 501 detection plane; is the i measurement angle; , M is the sampling point number; is the k Zernike coefficient related to .

[0092] S5, performing periodic function fitting on the tilt term and the defocus term in the Zernike coefficient sequence to separate the error aberration term introduced by the mechanical jitter of the θZ turntable 405, subtracting the error aberration term from the measured wave aberration information to obtain corrected real wave aberration information and a wavefront intensity distribution image.

[0093] Step S5 includes the following specific steps:

[0094] S51, from the measurement angle related to Z select low-order aberration coefficients in the Zernike coefficient sequence, including: X-direction tilt term coefficient , Y-direction tilt term coefficient and defocus term coefficient ; wherein each low-order aberration coefficient is obtained by linear superposition of objective lens real aberration coefficient and error aberration coefficient, and the expression formula is:

[0095] ;

[0096] In the formula, the low-order aberration coefficient is represented; the objective lens real aberration coefficient is represented; and the error aberration coefficient is represented.

[0097] Wherein, the error aberration introduced by the radial jitter amount and the end face jitter amount can be modeled as:

[0098] ;

[0099] In the formula, C T and C D is the sensitivity constant for converting mechanical displacement into Zernike coefficient. is the phase angle of the mechanical jitter error.

[0100] Due to mechanical processing and assembly, the mechanical jitter amounts and usually vary periodically with the measurement angle , and mainly contain a first-order harmonic component. Therefore, the embodiment performs harmonic analysis on the total aberration coefficient sequence collected, specifically step S52.

[0101] S52, Fourier transform or least square fitting is performed on each low-order aberration coefficient to extract the first-order harmonic component as the error aberration term , and the expression is:

[0102] ;

[0103] wherein, A k 、 B k is the amplitude of periodic tilt / defocus of mechanical runout in X / Y direction; C k is the constant term in the fitting residual (originated from the setup residual error).

[0104] S53, subtract the error aberration term from the measured low-order aberration coefficients to obtain the low-order aberration coefficients of the objective lens 401 under the measurement angle after correction of mechanical error:

[0105] ;

[0106] S54, combine the corrected low-order aberration coefficients with the high-order aberration coefficients (high-order aberration affected by slight mechanical runout can be ignored) in the ernike coefficient sequence related to the measurement angle Z to reconstruct the real wavefront intensity distribution image of the objective lens 401 under the measurement angle .

[0107] In some embodiments, after the test is completed, the operator can perform accurate adjustment on the objective lens 401 through the aberration adjustment assembly 402 based on the high-precision wavefront information until the wave aberration under all angles meets the design requirements.

[0108] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art, according to the technical solution and the inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for testing the aberrations of a microscope objective based on a Shack-Hartmann sensor, characterized in that The application is applied to a test system comprising an illumination module (3), an objective module (4) and a detection module (5), and comprises the following steps: S1, generating a standard point light source by the illumination module (3) to emit a standard spherical wave; S2, adjusting the positions of the modules to keep the modules and a to-be-tested objective (401) in the objective module (4) in a parallel state and on a same central reference optical axis, so that the focal point of the to-be-tested objective (401) coincides with the standard point light source; S3, rotating the to-be-tested objective (401) around the Z axis to a plurality of preset measurement angles by a θZ turntable (405) in the objective module (4), testing at each measurement angle, so that the spherical wave carries wavefront distortion after passing through the to-be-tested objective (401) and enters a Shack-Hartmann wavefront sensor (501) in the detection module (5), thereby obtaining a wavefront intensity distribution image distorted by the to-be-tested objective (401); S4, performing Zernike polynomial decomposition on the wavefront intensity distribution image obtained at each measurement angle to obtain wavefront difference information and a corresponding Zernike coefficient sequence; in step S4, the expression formula for performing Zernike polynomial decomposition on the wavefront intensity distribution image obtained at each measurement angle is: wherein is the wavefront intensity distribution image acquired at each measurement angle; x , y is the Cartesian coordinate of the Shack-Hartmann wavefront sensor (501) detection plane; is the i measurement angle; , M is the number of sampling points; is the k Zernike coefficient related to , , N is the sum of the coefficients of the Zernike polynomial decomposition; is the k Zernike polynomial, , is the normalized polar coordinate, , ; S5, performing periodic function fitting on tilt terms and defocus terms in the Zernike coefficient sequence to separate error aberration terms introduced by mechanical jumping of the θZ turntable (405), subtracting the error aberration terms from the measured wave aberration information to obtain corrected real wave aberration information and a wavefront intensity distribution image; step S5 comprises the following specific steps: S51、from the measurement angle related Z selecting low-order aberration coefficients in the Zernike coefficient sequence, including: X-direction tilt term coefficients , Y-direction tilt term coefficients and defocus term coefficients ; wherein each low-order aberration coefficient is obtained by linear superposition of an objective lens real aberration coefficient and an error aberration coefficient, and the expression formula is: wherein denotes a low order aberration coefficient; denotes a real objective aberration coefficient; denotes an error aberration coefficient; S52, Fourier transform or least square fitting is performed on each low-order aberration coefficient to extract a first-order harmonic component as an error aberration term ; S53, subtracting the error aberration term from the measured low order aberration coefficients to obtain the low order aberration coefficients of the objective (401) under test corrected for mechanical errors at the measurement angle under test: S54、combine the corrected low-order aberration coefficients with the high-order aberration coefficients in the Zernike coefficient sequence to reconstruct a real wavefront intensity distribution image of the objective lens (401) at the measurement angle Z ​​​ 2. The method of testing the aberrations of a microscope objective based on a Shack-Hartmann sensor according to claim 1, characterized in that In step S2, the three-dimensional position of the standard point light source is adjusted by rotating the θZ turntable (405) and observing the wavefront intensity distribution image of the Shack-Hartmann wavefront sensor (501) so that the intensity of the point in the wavefront intensity distribution image that does not change with the rotation of the θZ turntable (405) reaches the maximum, thereby completing the coincidence of the focal point of the to-be-tested objective (401) with the standard point light source.

3. Microscope objective aberration testing system based on a Shack-Hartmann sensor, characterized in that The application discloses a test method and a test system.

4. The micro-mirror aberration testing system based on Shack-Hartmann sensor according to claim 3, characterized in that, The objective lens module (4) comprises a to-be-tested objective lens (401), an aberration adjusting assembly (402), an objective lens adapter (403), an XY micro-adjusting hinge (404) and a theta Z turntable (405); the to-be-tested objective lens (401) is installed on the theta Z turntable (405) through the objective lens adapter (403), and the theta Z turntable (405) is used for driving the to-be-tested objective lens (401) to rotate around the Z-axis direction to different angles; the aberration adjusting assembly (402) comprises a plurality of independently adjustable micro-adjusting components and is used for micro-adjusting the lens positions in the to-be-tested objective lens (401) to control aberration; the XY micro-adjusting hinge (404) is arranged between the to-be-tested objective lens (401) and the theta Z turntable (405) and is used for adjusting the horizontal position of the to-be-tested objective lens (401), so that the optical axis of the to-be-tested objective lens (401) is kept coaxial with the rotating shaft of the theta Z turntable (405); and the theta Z turntable (405) is installed on a frame module (1).

5. The micro-mirror aberration testing system based on Shack-Hartmann sensor according to claim 3, characterized in that, The detection module (5) comprises a Shack-Hartmann wavefront sensor (501), a collimator (502), a five-dimensional adjusting frame (503), a Shack-Hartmann adapter (504) and a collimator adapter (505); the Shack-Hartmann wavefront sensor (501) is installed on the five-dimensional adjusting frame (503) and is placed above the to-be-tested objective lens (401), and the five-dimensional adjusting frame (503) is used for driving the sensor to translate along the X, Y and Z axes and rotate around the X and Y axes; the collimator (502) is used for establishing an objective lens measurement reference to ensure coaxiality and parallelism of the light path; and the Shack-Hartmann adapter (504) and the collimator adapter (505) are respectively used for fixing the Shack-Hartmann wavefront sensor (501) and the collimator (502) on a frame module (1) to keep the light path position stable.

6. The micro-mirror aberration testing system based on Shack-Hartmann sensor according to claim 3, characterized in that, The test system further comprises a frame module and a Z-direction module (2); the frame module comprises a profile frame (101), a bottom 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 a through hole for accommodating the Shack-Hartmann wavefront sensor (501) is formed in the top plate (103); the Z-direction module (2) is arranged on the bottom plate (102) and is used for driving the illumination module (3) to translate along the Z-axis direction to adjust the axial distance between the illumination module (3) and the objective lens module (4).

7. The micro-mirror aberration testing system based on Shack-Hartmann sensor according to claim 3, characterized in that, The wavelength of the LED light source (301) is adjustable, and the wavelength range is 320nm-1200nm.

8. The micro-mirror aberration testing system based on Shack-Hartmann sensor according to claim 3, characterized in that, The size of the focused light spot of the standard high-power objective lens (306) is 1-10 times the size of the light transmission hole (3071) of the focused light spot mask plate (307).

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