Flatness measurement system and method based on Shack-Hartmann wavefront sensor

Abstract

The invention relates to a planeness measurement system and method based on a Shack-Hartmann wavefront sensor, relates to the technical field of optical measurement, and solves the technical problems of high cost, environmental sensitivity and low vibration robustness in a planeness measurement method in the prior art. The measuring system comprises a light source module, a variable light attenuation module, a beam expanding module, a test element loading module and an imaging detection module which are sequentially arranged in the light path direction. According to the flatness measurement system based on the Shack-Hartmann wavefront sensor, the Shack-Hartmann wavefront sensor is adopted to replace a laser interferometer to carry out surface type detection on the surface of an optical element, height information of the surface is deduced through obtained phase data, and therefore flatness measurement is obtained. The flatness measurement method based on the Shack-Hartmann wavefront sensor has the advantages of high precision, large wavefront dynamic range, rapid real-time detection and the like, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and in particular to a flatness measurement system and method based on a Shaker-Hartmann wavefront sensor. Background Technology

[0002] Flatness deviations on the surfaces of high-precision optical components (such as mirrors, window mirrors, and prisms) introduce wavefront distortion, leading to aberrations such as spherical aberration, coma, and astigmatism, significantly reducing the performance of the optical system. In fields such as lithography exposure and semiconductor defect detection, optical systems typically consist of dozens to hundreds of optical components. The cumulative flatness error of a single component can severely reduce the reliability of the equipment, such as causing distortion of the lithographic pattern. Existing flatness detection methods are generally divided into contact and non-contact types. Contact methods use a coordinate measuring machine to perform point-by-point height scanning, fit an ideal plane, and then calculate the flatness. Non-contact methods use a laser interferometer to measure the optical path difference between the surface and the reference optical path to reconstruct the surface shape.

[0003] Currently, coordinate measuring machines (CMMs), as contact measurement tools, are widely used in precision manufacturing. However, flatness measurement typically requires measuring the height data of the entire surface. CMMs measure point-by-point using probes, which, for large flat surfaces, necessitates a large number of points to cover the entire surface to ensure sufficient sampling points. This results in excessively long measurement times and low efficiency for point-by-point measurements. Furthermore, contact measurement methods can damage optical components.

[0004] In contrast, laser interferometry, as a non-contact measurement method, offers advantages such as high precision and fast measurement speed. However, commercially available laser interferometers are costly and sensitive to temperature and vibration, requiring use in laboratories or even cleanrooms. Limited by its operating wavelength, the dynamic range (the maximum and minimum surface profile errors that can be measured) of laser interferometers is relatively small. When measuring large gradient wavefront distortions (such as local scratches, micro-pits, and overall bending), traditional interferometry may cause phase changes exceeding one wavelength (2π), leading to phase wrapping. This necessitates complex unwrapping algorithms, which are time-consuming and prone to introducing errors. Summary of the Invention

[0005] This invention aims to address the technical problems of high cost, environmental sensitivity, and low vibration robustness in existing flatness measurement methods, and provides a flatness measurement system and method based on a Shaker-Hartmann wavefront sensor.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A flatness measurement system based on a Shack-Hartmann wavefront sensor, comprising, arranged in sequence in the optical path direction: a light source module, a variable optical attenuation module, a beam expansion module, a test element loading module, and an imaging detection module;

[0008] Among them,

[0009] The light source module is a laser; the light source module is used to generate laser light;

[0010] The variable optical attenuation module is arranged in sequence in the optical path direction: a polarizer, a half-wave plate, and an analyzer; the variable optical attenuation module is used to attenuate the power of the laser light emitted by the laser;

[0011] The beam expansion module is arranged in sequence in the optical path direction: a first lens group and a second lens group; the beam expansion module is used to expand the beam;

[0012] The test element loading module is the optical element to be tested;

[0013] The imaging detection module is arranged in sequence in the optical path direction: a microlens array and a CCD camera; the imaging detection module is used as a Shack-Hartmann wavefront sensor.

[0014] In the above technical solution, the working wavelength of the laser is selected from the range of 193 / 266 / 355 nm.

[0015] In the above technical solution, the optical element to be tested is arranged on a five-axis optical element loading frame.

[0016] In the above technical solution, both the polarizer and the analyzer are polarization beam splitters with the same optical axis direction. By rotating the half-wave plate, the fast axis of the half-wave plate forms an angle θ with the linearly polarized light passing through the polarizer. After passing through the analyzer, the transmitted light power is cos 2 θ of the incident light power.

[0017] In the above technical solution, the beam expansion ratio of the beam expansion module is between two times and five times.

[0018] In the above technical solution, the focal length range of the first lens group is: -30 mm < f′1 < -15 mm; the focal length range of the second lens group is: 30 mm < f′2 < 60 mm.

[0019] A measurement method applicable to the above flatness measurement system based on a Shack-Hartmann wavefront sensor, comprising the following steps:

[0020] First, before measuring the surface shape of the optical element to be tested, calibrate the Shack-Hartmann wavefront sensor;

[0021] Then, the optical element under test is placed into the detection optical path, and wavefront reconstruction is performed by the Shaker-Hartmann wavefront sensor. The two wavefront reconstruction results are then differentially analyzed to remove the influence of incident laser wavefront distortion.

[0022] Finally, after obtaining the reconstructed wave, the wavefront data is converted into the height data of the optical element under test based on the laser's operating wavelength and the refractive index parameters of the optical element under test, thus obtaining the flatness measurement.

[0023] In the above technical solution, the calibration method for calibrating the Shak-Hartmann wavefront sensor is as follows: the expanded laser beam is incident parallel to the Shak-Hartmann wavefront sensor, and a wavefront reconstruction of the laser is performed.

[0024] The present invention has the following beneficial effects:

[0025] The planarity measurement method based on the Shaker-Hartmann wavefront sensor of the present invention has the advantages of high accuracy, large wavefront dynamic range (no need for unwrapping algorithm), and fast real-time detection, and has broad application prospects.

[0026] The present invention relates to a flatness measurement system based on a Shaker-Hartmann wavefront sensor for measuring the flatness of the surface of optical elements (such as mirrors, window mirrors, prisms, etc.). The system uses a Shaker-Hartmann wavefront sensor to replace the laser interferometer for surface shape detection of optical elements. The height information of the surface is derived from the obtained phase data, thereby obtaining the flatness measurement.

[0027] The planarity measurement system based on the Shak-Hartmann wavefront sensor of the present invention uses a Shak-Hartmann wavefront sensor with a working wavelength range of 193nm to 1100nm, which is compatible with commercially available 193 / 266 / 355nm lasers. The detector uses a CCD camera, which has the advantages of high sensitivity and low noise. Attached Figure Description

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 This is a schematic diagram of the flatness measurement system based on the Shaker-Hartmann wavefront sensor of the present invention.

[0030] Figure 2 A schematic diagram of wavefront reconstruction for a Shaker-Hartmann wavefront sensor.

[0031] The reference numerals in the figure are:

[0032] 1-Laser; 2-Polarizer; 3-Half-wave plate; 4-Analyzer; 5-First lens group; 6-Second lens group; 7-Optical element to be tested; 8-Microlens array; 9-CCD camera. Detailed Implementation

[0033] The inventive concept of this invention is as follows:

[0034] The planarity measurement system based on the Shak-Hartmann wavefront sensor of the present invention uses the Shak-Hartmann wavefront sensor to detect the surface shape of optical components. Through the combination of variable light attenuation and a CCD camera, as well as the design of an achromatic and low-aberration beam expansion module, the planarity measurement of optical components compatible with commercial lasers (193 / 266 / 355nm) in the ultraviolet band can be obtained.

[0035] The present invention will now be described in detail with reference to the accompanying drawings.

[0036] The planarity measurement system based on the Shaker-Hartmann wavefront sensor of the present invention, such as Figure 1 As shown, the optical path is provided with the following components in sequence: laser 1, polarizer 2, half-wave plate 3, analyzer 4, first lens group 5, second lens group 6, optical element to be tested 7, and Shaker-Hartmann wavefront sensor composed of microlens array 8 and CCD camera 9.

[0037] The optical components of the flatness measurement system based on the Shak-Hartmann wavefront sensor of this invention are mainly divided into five parts according to their application: a light source module, a variable light attenuation module, a beam expander module, a test element loading module, and an imaging detection module. The light source module is a laser 1, whose operating wavelength can be selected from the range of 193 / 266 / 355nm as required. The variable light attenuation module consists of a polarizer 2, a half-wave plate 3, and an analyzer 4; the beam expander module consists of a first lens group 5 and a second lens group 6; the test element loading module includes a high-precision five-axis optical element loading frame, on which the optical element to be tested 7 is mounted; the imaging detection module is a Shak-Hartmann wavefront sensor composed of a microlens array 8 and a matching CCD camera 9. All optical components and module groups are assembled and mounted on a pre-designed mechanical structure using centering.

[0038] The laser light emitted from laser 1 undergoes power attenuation via a variable optical attenuation module to protect the CCD camera 9 in the Shaker-Hartmann wavefront sensor. The polarizer 2 and analyzer 4 in this variable optical attenuation module are both polarization beam splitters with aligned optical axes. By rotating the half-wave plate 3, the fast axis of the half-wave plate 3 forms an angle θ with the linearly polarized light passing through polarizer 2. After passing through analyzer 4, the transmitted light power is the cosine of the incident light power. 2 θ. By changing the rotation angle of half-wave plate 3, the optical power of the laser can be continuously changed.

[0039] After power attenuation, the laser enters the beam expander module, which consists of a first lens group 5 and a second lens group 6. The first lens group 5 is composed of fused silica and calcium fluoride, and this part mainly corrects chromatic aberration and some spherical aberration and coma. The second lens group 6 is composed of fused silica, and this part mainly corrects spherical aberration and astigmatism.

[0040] The focal length range of the first lens group 5 is:

[0041] -30mm <f′1<-15mm

[0042] The focal length range of the second lens group 6 is:

[0043] 30mm <f′2<60mm

[0044] The beam-expanding module, composed of the first lens group 5 and the second lens group 6, has a beam-expanding magnification between two and five times.

[0045] The planarity measurement method based on the Shaker-Hartmann wavefront sensor of the present invention includes the following steps:

[0046] First, before measuring the surface profile of the optical element 7 to be tested, the Shak-Hartmann wavefront sensor needs to be calibrated. The calibration method is to directly allow the expanded laser beam to be incident parallel to the Shak-Hartmann wavefront sensor and perform a wavefront reconstruction of the laser.

[0047] Then, the optical element 7 to be tested is placed into the detection optical path through a five-dimensional platform (a five-axis optical element mounting frame), and wavefront reconstruction is performed by a Shaker-Hartmann wavefront sensor. The difference between the two wavefront reconstruction results can remove the influence of incident laser wavefront distortion.

[0048] Figure 2 This is a diagram illustrating the effect of reconstructing the projected wavefront of the element under test using the system of the present invention. Figure 2 As can be seen, the wavefront exhibits a large range of distortions (manifested as local curvature and abrupt, steep edges). This result demonstrates the advantage of the Shaker-Hartmann wavefront sensor in providing a large dynamic range wavefront measurement, which is not available in traditional laser interferometers (laser interferometers require complex unwrapping algorithms when dealing with this type of problem, which are time-consuming and prone to errors).

[0049] Finally, after obtaining the reconstructed wavefront, based on the operating wavelength of laser 1 and the refractive index parameters of the optical element under test 7, the wavefront data can be converted into the height data of the optical element under test 7, thereby obtaining the flatness measurement.

[0050] The planarity measurement system based on the Shaker-Hartmann wavefront sensor of the present invention, after experimental testing, can easily reconstruct wavefront distortion in dozens of wavelength ranges in an industrial environment (without a laboratory environment), thereby obtaining the planarity measurement of the optical element under test.

[0051] The planarity measurement system based on the Shaker-Hartmann wavefront sensor of the present invention has the advantages of high accuracy, large wavefront dynamic range (no need for unwrapping algorithm), and fast real-time detection, and has broad application prospects.

[0052] The present invention relates to a flatness measurement system based on a Shaker-Hartmann wavefront sensor for measuring the flatness of the surface of optical elements (such as mirrors, window mirrors, prisms, etc.). The system uses a Shaker-Hartmann wavefront sensor to replace the laser interferometer for surface shape detection of optical elements. The height information of the surface is derived from the obtained phase data, thereby obtaining the flatness measurement.

[0053] The planarity measurement system based on the Shak-Hartmann wavefront sensor of the present invention uses a Shak-Hartmann wavefront sensor with a working wavelength range of 193nm to 1100nm, which is compatible with commercially available 193 / 266 / 355nm lasers. The detector uses a CCD camera, which has the advantages of high sensitivity and low noise.

[0054] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A flatness measurement system based on a Shaker-Hartmann wavefront sensor, characterized in that, Including, arranged in sequence along the optical path direction: a light source module, a variable optical attenuation module, a beam expansion module, a test element loading module, and an imaging detection module; Among them, The light source module is a laser (1); the light source module is used to generate laser light; The variable optical attenuation module includes, arranged in sequence along the optical path direction: a polarizer (2), a half-wave plate (3), and an analyzer (4); the variable optical attenuation module is used to attenuate the power of the laser light emitted by the laser (1); The beam expansion module includes, arranged in sequence along the optical path direction: a first lens group (5) and a second lens group (6); the beam expansion module is used to expand the beam; The test element loading module is a to-be-tested optical element (7); The imaging detection module includes, arranged in sequence along the optical path direction: a microlens array (8) and a CCD camera (9); the imaging detection module is used as a Shack-Hartmann wavefront sensor.

2. The flatness measurement system based on the Shaker-Hartmann wavefront sensor according to claim 1, characterized in that, The working wavelength of the laser (1) is selected from the range of 193 / 266 / 355 nm.

3. The flatness measurement system based on the Shaker-Hartmann wavefront sensor according to claim 1, characterized in that, The to-be-tested optical element (7) is arranged on a five-axis optical element loading frame.

4. The flatness measurement system based on the Shaker-Hartmann wavefront sensor according to claim 1, characterized in that, Both the polarizer (2) and the analyzer (4) are polarization beam splitters with the same optical axis direction. By rotating the half-wave plate (3), the fast axis of the half-wave plate (3) forms an angle θ with the linearly polarized light passing through the polarizer (2). After passing through the analyzer (4), the transmitted light power is the cosine of the incident light power. 2 θ.

5. The flatness measurement system based on the Shaker-Hartmann wavefront sensor according to claim 1, characterized in that, The beam expansion ratio of the beam expansion module is between two and five times.

6. The flatness measurement system based on the Shaker-Hartmann wavefront sensor according to claim 5, characterized in that, The focal length range of the first lens group (5) is: -30 mm < f′1 < -15 mm; the focal length range of the second lens group (6) is: 30 mm < f′2 < 60 mm.

7. A measurement method applicable to the flatness measurement system based on the Shaker-Hartmann wavefront sensor as described in claim 1, characterized in that, Including the following steps: First, before measuring the surface shape of the to-be-tested optical element (7), calibrate the Shack-Hartmann wavefront sensor; Then, place the to-be-tested optical element (7) into the detection optical path, perform wavefront reconstruction through the Shack-Hartmann wavefront sensor, and perform difference on the results of the two wavefront reconstructions to remove the influence of the incident laser wavefront distortion; Finally, after obtaining the reconstructed wavefront, according to the working wavelength of the laser (1) and the refractive index parameter of the to-be-tested optical element (7), convert the wavefront data into the height data of the to-be-tested optical element (7) to obtain the measurement of flatness.

8. The flatness measurement method based on the Shaker-Hartmann wavefront sensor according to claim 7, characterized in that, The calibration method for calibrating the Shack-Hartmann wavefront sensor is: make the expanded laser light incident on the Shack-Hartmann wavefront sensor parallelly and perform wavefront reconstruction of the laser light once.

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