Micro-nano structure pattern sample automatic focusing device and method

Abstract

The application discloses a kind of high-transparency micro-nano structure pattern sample automatic focusing device and method, device includes computer, laser, CCD, mirror, objective lens, imaging lens and spectral element etc., micro-nano structure pattern sample is placed on object table, and the diameter data of laser transmission light spot collected by computer processing CCD is calculated to obtain the surface position of current sample to be measured, control electric focusing lifting platform with objective lens moves, and automatic focusing is completed.The application uses the diameter of transmission light spot collected by CCD as focusing criterion, improves the detection precision of sample thickness variation, reduces the influence of high-transparency area on sample and high-complexity micro-nano structure on light spot diameter measurement, to improve the accuracy of defocus amount determination, realize the automatic focusing of micro-nano structure pattern sample at higher speed, higher stability, higher adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-speed focusing of high-transparency and high-complexity micro-nano structure pattern samples, and is a high-speed, high-precision and high-adaptability focusing control device and method based on transmission laser spot diameter for detecting defocus amount, which can be used for automatic focusing of high-transparency and high-complexity micro-nano structure pattern samples. BACKGROUND

[0002] When micro-nano structure optical elements and storage carriers are subjected to microscopic imaging and information reading, high-speed automatic focusing technology is of great significance to improve reading efficiency. According to its principle, the existing automatic focusing technology is mainly divided into two types: one is based on image processing technology to search the range and evaluate the focusing, and the other is based on auxiliary light spot to detect and calculate the defocus amount and focus. The method based on image processing technology needs to search in the whole focusing range and perform a large number of image processing operations to determine the focal plane position, so the focusing process takes a long time. The method based on auxiliary light spot to detect and focus usually falls a beam of auxiliary light on the sample surface, and judges the defocus distance according to the shape and size of the reflected light spot on the sample surface, and automatically focuses accordingly. This method has fast processing speed and is widely used for high-reflectivity samples, but when it is applied to high-transparency and high-complexity pattern samples, the reflectivity of the sample surface is low, and the reflected light spot has problems such as weak intensity and low signal-to-noise ratio, which affects the automatic focusing effect.

[0003] Patent No. CN113206950A discloses a high-speed tracking method for micro-nano structure pattern samples, which includes a computer, an illumination and imaging module, a dichroic prism, a focusing mechanism, a piezoelectric ceramic, an objective lens, a workpiece table, a detector, an astigmatism module, a light splitting module, a beam expander, a laser and a controller. The micro-nano structure pattern sample to be tracked is placed on the workpiece table, and the surface of the micro-nano structure pattern sample to be tracked is clearly imaged by the up and down movement of the focusing mechanism. Adjust the beam expander so that the laser emitted by the laser is focused on the surface of the micro-nano structure pattern sample to be tracked, and synchronously control the workpiece table and the controller to complete the movement and tracking of the micro-nano structure pattern sample to be tracked. The computer communicates with the CCD in the illumination and imaging module, the workpiece table and the controller in real time. The high-speed tracking method for micro-nano structure pattern samples can automatically track the micro-nano structure pattern samples at high speed, high precision and high sensitivity, and ensure clear imaging of the micro-nano structure pattern, which provides guarantee for subsequent reading and detection. However, when this invention is applied to high-transparency micro-nano structure pattern samples, the reflectivity of the sample surface is low, and the quality and signal-to-noise ratio of the reflected light spot will affect the judgment of the defocus amount, thereby affecting the automatic focusing effect. SUMMARY

[0004] The present application aims at solving the instability problem of the prior art technology of automatic focusing according to the diameter variation of the reflected light spot formed by the incident light beam when applied to high-transparency and high-complexity pattern samples. The actual defocus amount of the sample surface is calculated by receiving the light spot signal formed by the light beam transmitted through the sample by the CCD, and high-speed automatic focusing of the high-transparency and high-complexity micro-nano structure pattern sample is realized.

[0005] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0006] In one aspect, the present application provides an automatic focusing device for micro-nano structure pattern samples, comprising an illumination imaging module, a stage for placing the micro-nano structure pattern sample, a laser, a CCD, a controller and a computer, characterized in that it further comprises a first focusing mechanism for placing a first objective lens and a second focusing mechanism for placing a second objective lens.

[0007] The computer is in communication connection with the illumination imaging module, the CCD and the controller respectively; the controller is in communication connection with the stage, the first focusing mechanism and the second focusing mechanism respectively.

[0008] The laser emitted by the laser is converged by the second objective lens and irradiated on the bottom of the micro-nano structure pattern sample, is transmitted through the micro-nano structure pattern sample, is converged by the converging lens after passing through the first objective lens above the micro-nano structure pattern sample, and is imaged by the CCD; the first focusing mechanism drives the first objective lens above the stage to move, so that the surface of the stage is at the focal position of the first objective lens; the micro-nano structure pattern sample is placed on the stage, and the distance from the upper surface of the stage to the upper surface of the current micro-nano structure pattern sample is calculated by the computer processing the diameter data of the laser transmitted light spot; the second focusing mechanism drives the second objective lens to move up and down, so as to complete the automatic focusing.

[0009] In another aspect, the present application further provides an automatic focusing method for micro-nano structure pattern samples, characterized in that the method comprises the following steps:

[0010] a) The first focusing mechanism drives the first objective lens to move, so that the focal plane of the first objective lens coincides with the upper surface of the stage, and at this time the distance between the first objective lens and the upper surface of the stage is s0 mm.

[0011] b) The laser is controlled, the power of the laser is set to a mW, the beam expander is adjusted so that the convergence angle of the laser emitted by the second objective lens is I, and the second focusing mechanism drives the second objective lens to move, so that the light beam convergence point of the second objective lens coincides with the upper surface of the stage.

[0012] c) Control the first focusing mechanism to drive the first objective lens to move downward for a total stroke of k pm, with a movement resolution of b nm. At the same time, record the change in the object distance value of the converging point of the light beam of the second objective lens to the object distance of the first objective lens, Δs, and the spot diameter d received by the CCD at different positions of the first focusing mechanism c .

[0013] d) Fit the data obtained in the previous step to obtain a fitting curve of the spot diameter d c and the change in the object distance value Δs.

[0014] e) Control the first focusing mechanism to return to s0, and place the micro-nano structure pattern sample to be tested on the upper surface of the stage. According to the spot diameter received by the CCD at this time, combined with the fitting curve obtained in step d), the change in the converging point of the outgoing light beam of the second objective lens relative to the object distance of the first objective lens caused by the refraction of the sample can be calculated.

[0015] f) According to the law of refraction, the distance between the upper surface of the stage and the upper surface of the micro-nano structure pattern sample can be calculated by the value of Δs and the refractive index n of the sample where the relationship between I and I' is sin I = n sin I'. Control the first focusing mechanism to drive the first objective lens to move upward by a distance of c, which completes the auto-focusing of the high-transparency micro-nano structure pattern sample.

[0016] Compared with the prior art, the technical effects of the present application are as follows:

[0017] 1) The spot size is used to react to the sample surface position, and is directly used as a criterion to calculate the distance and complete the focusing process. Compared with the scheme of image processing and judging the focusing of the sample surface information, the present application has smaller calculation amount and faster processing speed.

[0018] 2) Compared with the method of using reflected light spot measurement results as the defocusing criterion in the prior application, the present application uses transmitted light spot measurement results as the defocusing criterion. When applied to the auto-focusing and tracking of high-transparency low-reflectivity samples, the problem of low signal-to-noise ratio of the reflected light spot and poor focusing effect caused by the complex structure and low reflectivity of the sample can be avoided. It has higher adaptability and stability. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The present application is a high-transparency high-complexity micro-nano structure pattern sample focusing device schematic diagram.

[0020] Figure 2 The present application is a schematic diagram of the change of the laser spot with the sample thickness.

[0021] Figure 3 The present application is a real spot change trend chart.

[0022] Figure 4 A graph showing the relationship between the change in object distance and the spot diameter of the objective lens of this invention; Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments and accompanying drawings, but these should not be construed as limiting the scope of protection of the present invention.

[0024] Example 1

[0025] like Figure 1 As shown, the high-transparency micro / nano structure patterned sample autofocus device includes an illumination imaging module 1, a first reflector 2, a beam splitter prism 3, a first focusing mechanism 4, a first objective lens 5, a micro / nano structure patterned sample 6, a stage 7, a second objective lens 8, a second focusing mechanism 9, a second reflector 10, a beam expander 11, a laser 12, a converging lens 13, a CCD 14, a controller 15, and a computer 16.

[0026] The laser emitted by the laser 12 passes through the beam expander 11, is reflected by the second mirror 10, and then passes through the second objective lens 8 to reach the bottom surface of the micro-nano structure patterned sample 6. The transmitted light passes through the first objective lens 5, is reflected by the beam splitter 3, and then passes through the converging lens 13 to reach the CCD 14.

[0027] The stage 7, the first focusing mechanism 4, and the second focusing mechanism 9 communicate with the controller 15; the illumination imaging module 1, the first CCD 14, and the controller 15 communicate with the computer 16.

[0028] A focusing method for high-transparency, high-complexity micro / nano structure patterned samples includes the following steps:

[0029] a) Control the first focusing mechanism 4 to drive the first objective lens 5 to move so that the focal plane of the first objective lens 5 coincides with the upper surface of the stage 7. At this time, the distance s0 between the first objective lens 5 and the upper surface of the stage 7 is 2.45mm.

[0030] b) Control the laser and set its power to 40mW; adjust the beam expander 11 to achieve the convergence angle of the laser emitted from the second objective lens 8. The second focusing mechanism 9 is controlled to move the second objective lens 8 so that the beam convergence point of the second objective lens 8 coincides with the upper surface of the stage 7.

[0031] c) Control the first focusing mechanism 4 to move the first objective lens 5 downwards for a total distance of 250 μm, with a motion resolution of 2 nm. Simultaneously record the change in object distance Δs between the beam convergence point of the second objective lens 8 and the first objective lens 5 at different positions of the first focusing mechanism 4, as well as the diameter d of the light spot received by the CCD 14. c .

[0032] d) Fit the data obtained in the previous step to obtain the spot diameter d.c fitting curve of the change amount of object distance value As.

[0033] e) Control the first focusing mechanism 4 to return to s0=2.45mm, place the micro-nano structure pattern sample 6 on the upper surface of the object table 7, and according to the spot diameter received by the CCD 14 at this time, combined with the fitting curve obtained in step d), the change amount As of the exit beam convergence point of the second objective lens 8 relative to the object distance of the first objective lens 5 caused by the refraction of the sample can be obtained.

[0034] f) According to the refraction law, the distance from the upper surface of the micro-nano structure pattern sample 6 to the upper surface of the object table 7 can be calculated by the value of As and the refractive index n of the sample wherein the relationship between I and I' is sin I=n*sin I'. Control the first focusing mechanism 4 to move the first objective lens 5 upward by a distance c, that is, the automatic focusing of the high-transparency micro-nano structure pattern sample 6 is completed.

Claims

1. An automatic focusing device for micro-nano structure pattern sample, comprising an illumination imaging module (1), a stage (7) for placing a micro-nano structure pattern sample (6), a laser (12), a CCD (14), a controller (15) and a computer (16), characterized in that, The first focusing mechanism (4) is used for placing the first objective lens (5), and the second focusing mechanism (9) is used for placing the second objective lens (8); The computer (16) is in communication connection with the illumination imaging module (1), the CCD (14) and the controller (15) respectively; the controller (15) is in communication connection with the object table (7), the first focusing mechanism (4) and the second focusing mechanism (9) respectively; The laser (12) exits the laser and converges through the second objective lens (8), irradiates the bottom of the micro-nano structure pattern sample (6), transmits through the micro-nano structure pattern sample (6), and converges through the converging lens after the transmitted light passes through the first objective lens (5) above the micro-nano structure pattern sample (6), and is imaged by the CCD; the first focusing mechanism (4) drives the first objective lens (5) above the objective table to move, so that the surface of the objective table is in the focal position of the first objective lens (5), the micro-nano structure pattern sample (6) is placed on the objective table, and the diameter data of the laser transmission light spot is calculated by the computer to calculate the distance from the upper surface of the objective table to the upper surface of the current micro-nano structure pattern sample (6), which specifically includes calculating the diameter d c The data corresponding to the distance change value Δs is calibrated and curve fitting is performed; the first focusing mechanism (4) is controlled to return to the distance s0, the micro-nano structure pattern sample (6) to be measured is placed on the upper surface of the objective table (7), and the change amount Δs1 of the converging point of the outgoing light beam of the second objective lens (8) relative to the first objective lens (5) caused by the refraction of the micro-nano structure pattern sample (6) to be measured is obtained according to the spot diameter received by the CCD (14) at this time and the fitting curve obtained in step 5; the distance c from the upper surface of the objective table (7) to the upper surface of the micro-nano structure pattern sample (6) is calculated, and the formula is as follows: In the formula, sinI=n*sinI', n is the refractive index of the micro-nano structure pattern sample (6); I is the convergence angle of the laser emitted by the laser (12) after being emitted by the second objective lens (8); the second focusing mechanism (9) drives the second objective lens (8) to move up and down, so as to complete the automatic focusing.

2. An automatic focusing method for a micro-nano structure pattern sample, characterized in that, The method comprises the following steps: Step 1: control the first focusing mechanism (4) to make the focal plane of the first objective lens (5) coincide with the upper surface of the object table (7), so that the distance s0 between the first objective lens (5) and the upper surface of the object table (7) is obtained; Step 2: set the power of the laser (12) as a, adjust the beam expander (11) to make the convergence angle of the laser emitted by the laser (12) after being emitted by the second objective lens (8) as I; Step 3: control the second focusing mechanism (9) to make the beam convergence point of the second objective lens (8) coincide with the upper surface of the object table (7); Step 4. Control the first focusing mechanism (4) to move the first objective lens (5) up and down in the stroke range, and record the change of the object distance Δs of the light beam convergence point of the second objective lens (8) to the first objective lens (5) and the diameter d of the light spot received by the CCD (14) at different positions of the first focusing mechanism (4) c ; Step V. The spot diameter d c corresponding to the data Δs and curve fitting; Step 6: control the first focusing mechanism (4) to return to the distance s0, place the micro-nano structure pattern sample (6) to be measured on the upper surface of the object table (7), and according to the spot diameter received by the CCD (14) at this time, the fitting curve obtained in step 5 is combined to obtain the change amount Δs1 of the object distance of the second objective lens (8) caused by the refractive index of the micro-nano structure pattern sample (6) to be measured; Step 7: calculate the distance c from the upper surface of the object table (7) to the upper surface of the micro-nano structure pattern sample (6), and the formula is as follows: In the formula, sinI=n*sinI', n is the refractive index of the micro-nano structure pattern sample (6); Step 8: control the first focusing mechanism (4) to move the first objective lens (5) upward by the distance c, that is, the automatic focusing of the micro-nano structure pattern sample (6) is completed.

3. The method of claim 2, wherein the method further comprises: The micro-nano structure pattern sample (6) comprises a pattern region with optical contrast and a non-pattern region, and the pattern region has a higher optical reflectivity, and the non-pattern region has a higher optical transmittance.

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