Ultraviolet light field regulation and control method for driving correction-free spatial light modulation through composite algorithm

Abstract

The invention discloses an ultraviolet light field regulation and control method for driving correction-free spatial light modulation through a composite algorithm, and the method comprises the following steps: feeding laser into a whole polarization state, carrying out the beam expansion of the laser, and enabling the laser to enter a spatial light modulator; laser enters the spatial light modulator, is modulated and reflected, and is split after being reflected, one path of feedback light enters the industrial camera to serve as feedback light, and the other path of light serves as output light; the industrial camera receives light spot information, a Gerchberg-Saxton algorithm is utilized in the computer to carry out preliminary mask calculation, a series of initial populations are generated, and then a genetic algorithm is utilized to carry out iteration to obtain an optimal phase mask. Regulation and control are achieved through the composite algorithm, gamma correction does not need to be conducted on the spatial light modulator, and therefore the problem that an existing spatial light modulator does not have ultraviolet correction data is effectively solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of light field regulation, and particularly relates to a method for regulating an ultraviolet light field by using a composite algorithm to drive uncorrected spatial light modulation. BACKGROUND

[0002] Due to the characteristics of high photon energy, low thermal effect and strong focusing ability, ultraviolet band lasers have been applied in the fields of industrial precision manufacturing, medical treatment, biotechnology, material spectrum analysis, environmental dynamics, microelectronics and semiconductor manufacturing. In the field of photolithography, the quality of a laser wavefront is particularly important for processing. Size and shape deviations can introduce line width errors and abnormal overlapping areas, resulting in pattern defects; uneven energy distribution can cause thermal damage, and excessive local energy can cause overexposure of photoresist; and a light spot center offset can cause adjacent pattern overlapping and short circuit in a chip.

[0003] In a traditional method, a spatial light modulator needs to be gamma-corrected to adapt to a special wavelength. When a conventional spatial light modulator is applied in the ultraviolet band, the optical path is greater than the calibration value, and the voltage value on the liquid crystal is not in a linear relationship with the loaded gray value (represented as phase delay), so gamma correction is needed, and the contradiction between high-quality, high-robustness regulation and high-efficiency regulation cannot be resolved. If gamma correction is performed again, the main methods include an interference phase calibration method and a diffraction phase calibration method (Li R, Cao L. Progress in Phase Calibration for Liquid Crystal Spatial Light Modulators [J]. Applied Sciences, 2019, 9(10): 2012.), but both methods need to build an optical path. SUMMARY

[0004] To solve the contradiction between the operation of a spatial light modulator in an ultraviolet laser wavelength environment and high-quality regulation and improve the robustness of light field regulation, the application provides a method for regulating an ultraviolet light field by using a composite algorithm to drive uncorrected spatial light modulation, adjusts the polarization state of laser and expands the laser beam, and then passes the laser through a spatial light modulator. After being split by a beam splitter prism, data is collected by using an industrial camera, a mask is calculated, and the mask is fed back to the spatial light modulator. A local optimal mask is obtained by using a Gerchberg-Saxton algorithm, and the mask is optimized by using a genetic algorithm. The method can be used to modulate in the ultraviolet wavelength, improve the quality of light field regulation in a special wavelength band, and improve the robustness of the system.

[0005] The application is implemented by at least one of the following technical solutions.

[0006] A method for regulating an ultraviolet light field by using a composite algorithm to drive uncorrected spatial light modulation, comprising the following steps:

[0007] A. The laser is sent into a whole polarization state, and then the laser is expanded and incident on the spatial light modulator;

[0008] B. The laser incident on the spatial light modulator is modulated and reflected, and the reflected light is incident on the beam splitter prism, one way of light is incident on the industrial camera as feedback light, and the other way of light is output as output light;

[0009] C. The industrial camera receives the spot information and performs preliminary mask calculation in the computer using the Gerchberg-Saxton algorithm;

[0010] D. A series of initial populations are generated from the obtained mask, and the genetic algorithm is used to obtain the optimal phase mask through iteration since the genetic algorithm is not sensitive to the voltage-phase correspondence;

[0011] F. The spatial light modulator is loaded with the iteratively obtained phase mask to realize the regulation of the ultraviolet waveband laser light field without the need for gamma correction of the spatial light modulator.

[0012] Preferably, the laser is expanded in step A by using an expansion system including two plano-convex lenses and a biconvex lens, and the biconvex lens is located between the two plano-convex lenses. The specific steps of expanding the laser are as follows: fixing one of the plano-convex lenses, adjusting the position of the biconvex lens to control the magnification, adjusting the position of the other plano-convex lens, loading a Fresnel half-wave band into the spatial light modulator, and the focal length is the distance between the industrial camera and the spatial light modulator. When the outgoing light is parallel light, the convergence point on the industrial camera is extremely bright.

[0013] Preferably, in the Gerchberg-Saxton algorithm in step C, since the industrial camera pixels are different from the spatial light modulator pixels, the actual physical size is different, so an adjustment factor Δ 调整 is introduced in the algorithm, and the relationship is as follows:

[0014]

[0015] where Δx 空间光调制器 is the size of the spatial light modulator pixels, Δx 工业相机 is the size of the industrial camera pixels, and the specific scaling operation is as follows:

[0016] U 工业相机 [r,s]=Δ 调整 U 空间光调制器 [p,q]

[0017] where U 工业相机 is the frequency domain amplitude size obtained by the industrial camera, and U 空间光调制器The amplitude in the frequency domain of the light spot on the spatial light modulator.

[0018] In the Gerchberg-Saxton algorithm in step C, an offset adjustment value x 调整 and y 调整 is introduced to calibrate the difference between the two, and the adjusted relationship is:

[0019]

[0020] where ΔΦ 线性 is the frequency domain offset caused by the introduction of the offset, which actually moves the light spot on the industrial camera to the center point in the spatial domain.

[0021] In step D, a genetic algorithm is preferably used, and the main operation is to generate an initial population by floating the mask and phase generated in the Gerchberg-Saxton algorithm up and down by a numerical value; when calculating the weight, the phase mask is loaded once, and the industrial camera reads the light spot information once until the iteration ends.

[0022] The ultraviolet light field regulation system for implementing the method comprises a laser source, a polarization adjustment system, a beam expansion system, a spatial light modulator, a beam splitter prism, an industrial camera and a computer arranged in sequence along an optical path, the polarization adjustment system is used to adjust the polarization state of the laser, the beam expansion system is used to expand the laser beam, and the expanded light is incident on the spatial light modulator, the spatial light modulator is used to adjust and reflect the incident light, the industrial camera is connected to a feedback optical path, and the computer is connected to the industrial camera and the spatial light modulator.

[0023] Preferably, the glass materials used are all ultraviolet fused quartz.

[0024] Preferably, the polarization adjustment system comprises a polarization beam splitter prism and a half-wave plate, the polarization beam splitter prism is used to obtain linearly polarized light, and the half-wave plate is used to adjust the polarization direction.

[0025] Preferably, the laser source uses a semiconductor laser as a test light source.

[0026] Preferably, the beam expansion system comprises two plano-convex lenses and a biconvex lens, and the biconvex lens is located between the two plano-convex lenses. The materials of the plano-convex lenses and the biconvex lens are all ultraviolet fused quartz.

[0027] The spatial light modulator is a phase-type reflective spatial light modulator, and the pixel size is 4.5 microns.

[0028] The industrial camera has a pixel size of 2.2 microns, and the exposure mode is line-by-line exposure.

[0029] Optionally, the industrial camera using global exposure can obtain higher image quality, so as to improve the algorithm performance.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] By using the genetic algorithm combined with the Gerchberg-Saxton algorithm, the present application can directly apply the ultraviolet band to the spatial light modulator, without adjusting the gamma curve of the spatial light modulator, and can realize efficient and high-quality spot regulation in a short time, thereby solving the contradiction between the operation of the spatial light modulator in the ultraviolet laser wavelength environment and the high-quality regulation, and improving the robustness of the light field regulation. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A light path design diagram of the ultraviolet band light field regulation method of the spatial light modulator of the embodiment of the present application;

[0033] Figure 2 A step flowchart of the ultraviolet band light field regulation method of the spatial light modulator of the embodiment of the present application;

[0034] Figure 3 A spot shape schematic diagram not subjected to the light field regulation method in the embodiment of the present application;

[0035] Figure 4 A spot shape schematic diagram after iteration by the Gerchberg-Saxton algorithm in the embodiment of the present application;

[0036] Figure 5 A spot shape schematic diagram after iteration by the genetic algorithm in the embodiment of the present application. DETAILED DESCRIPTION

[0037] In order to make the above objectives, characteristics and advantages of the present application more apparent and comprehensible, the technical solutions of the present application will be further described in detail below with reference to the accompanying drawings and specific implementation examples. It should be pointed out that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0038] It should be noted that the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above-mentioned drawings are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or modules or units does not have to be limited to only those steps or modules or units clearly listed, but can include other steps or modules or units not clearly listed or inherent to these processes, methods, products or devices.

[0039] As Figure 1 ,Figure 2 As shown, the method for controlling ultraviolet light field by using a composite algorithm to drive a non-corrected spatial light modulation device provided by the embodiment of the application comprises the following steps:

[0040] A. The laser is sent to a polarization adjustment system to adjust the polarization state, and the laser is expanded by a beam expanding system and then incident on a spatial light modulator;

[0041] B. The laser incident on the spatial light modulator is modulated and reflected, and the reflected light is incident on a beam splitter prism, one-way light is incident on an industrial camera as feedback light, and the other way light is output as output light;

[0042] C. The industrial camera receives the light spot information, and a Gerchberg-Saxton algorithm is used to perform fast preliminary mask calculation in a computer;

[0043] D. A series of initial populations are generated by using the obtained mask, and a phase mask is obtained by using a genetic algorithm to iterate, so as to gradually approach an optimal solution;

[0044] F. After the mask data is saved, the phase mask obtained by iteration in step D is only needed to be loaded in the spatial light modulator, so that the laser spot of any wavelength can be controlled with high quality.

[0045] In one of the embodiments of the application, the polarization adjustment system comprises a polarization beam splitter prism and a half-wave plate, and the influence of the polarization state transformation on the wavefront performance does not need to be considered. During the control, the linearly polarized light is obtained by sending the multimode laser into the polarization beam splitter prism, and then the polarization direction is adjusted by using the half-wave plate.

[0046] In one of the embodiments of the application, the beam expanding system comprises two plano-convex lenses and a biconvex lens. In order to reduce the aberration caused by the ultraviolet band material, the plano-convex lens with a focal length of 35 mm and a convex surface facing the incident surface is used as the incident surface, and then a 30 mm biconvex lens, a 100 mm plano-convex lens with a convex surface facing the exit surface are used. The adjustable beam expanding system can effectively reduce the spherical aberration. The beam expanding system can realize a maximum magnification of about 6 times for the spot size.

[0047] The specific steps of step A for expanding the laser are as follows: the position of the first plano-convex lens is fixed, the position of the central biconvex lens is adjusted to control the magnification, the position of the last plano-convex lens is adjusted, and a Fresnel half-wave band is loaded in the spatial light modulator. The focal length is the distance between the industrial camera and the spatial light modulator. When the exit light is parallel light, the convergence point on the industrial camera is extremely bright.

[0048] In one of the embodiments of the application, in step A, the expanded spot is 3 times the original size.

[0049] In one of the embodiments of the present application, in step B, the splitting ratio of the splitting prism is feedback light: output light = 1:9, i.e. 10% of the light incident on the splitting prism is incident on the industrial camera as feedback light, and 90% of the light is output as output light.

[0050] In one of the embodiments of the present application, the optical device used is ultraviolet fused quartz material. The lenses, half-wave plates, polarization beam splitting prisms, splitting prisms, and mirrors used are all ultraviolet fused quartz material, because the spot distortion before modulation has little effect on the result, and because ordinary quartz glass and other materials have strong absorption of ultraviolet waveband light, which has a large effect on light intensity, and the remaining glass materials that can be used in the ultraviolet waveband are relatively expensive.

[0051] In the Gerchberg-Saxton algorithm in step C, because the pixels of the industrial camera and the pixels of the spatial light modulator are different, the actual physical dimensions are different, so an adjustment factor Δ is introduced in the Gerchberg-Saxton algorithm 调整 , and the relationship is as follows:

[0052]

[0053] where Δx 空间光调制器 is the size of the pixels of the spatial light modulator, Δx 工业相机 is the size of the pixels of the industrial camera, and the specific scaling operation is as follows:

[0054] U 工业相机 [r,s] = Δ 调整 U 空间光调制器 [p,q]

[0055] where U 工业相机 [r,s] is the frequency domain amplitude size obtained by the industrial camera, U 空间光调制器 [p,q] is the frequency domain amplitude size on the spatial light modulator corresponding to the spot, and r, s are the discrete coordinates in space in the industrial camera, and p, q are the discrete coordinates in space in the spatial light modulator.

[0056] In the Gerchberg-Saxton algorithm in step C, because the pixels of the industrial camera and the pixels of the spatial light modulator are different, the actual physical dimensions are different, so an adjustment factor Δ is introduced in the Gerchberg-Saxton algorithm 调整 and y 调整 are introduced to calibrate the difference between the two, and the adjusted relationship

[0057]

[0058] where Δφ 线性In order to introduce the frequency domain offset caused by the offset, the spot on the industrial camera is actually moved to the center point in the space, m and n are spatial coordinates, and k and l are frequency domain coordinates after Fourier transform.

[0059] In the Gerchberg-Saxton algorithm, an adjustment factor is introduced to match the size of the spatial light modulator and the industrial camera pixel. An offset adjustment value is introduced to match the non-coincidence of the spot in the physical scale of the spatial light modulator and the industrial camera. In the actual code running process, the Fourier transform is first performed on the obtained spot information, the amplitude in the frequency domain of the spot information is adjusted by the adjustment factor, and the actual frequency position is adjusted by the offset adjustment value, so that the actual position and actual size of the spot in the spatial light modulator and the industrial camera are one-to-one corresponding.

[0060] In one embodiment of the present application, a genetic algorithm is used in step D, and the main operation is to randomly float up and down the mask and phase generated in the Gerchberg-Saxton algorithm by a preset value, and the value of the preset value depends on the difference between the gamma correction of the current spatial light modulator and the target wavelength to generate an initial population. When calculating the weight, load the phase mask once, and the industrial camera reads the spot information once until the iteration ends.

[0061] The optimization parameters of the genetic algorithm include: the population size is 50-200, the number of offspring is 50% of the initial population, and the mutation probability is 0.01-0.1.

[0062] The information of the actual spot is obtained by using the industrial camera, the phase mask is calculated by using the computer, and is reloaded into the spatial light modulator, and the root mean square error of the actual spot and the target spot is calculated, and the mask with lower error rate has higher weight.

[0063] In one embodiment of the present application, by comparing Figure 3 and Figure 4 It can be found that the intensity of the obtained spot after adjustment by the genetic algorithm is more in line with the corresponding requirements. By correcting the mask by the genetic algorithm, the phase error caused by the absence of gamma correction can be compensated, so that the spatial light modulator can still control the ultraviolet laser spot with high quality in the ultraviolet band.

[0064] The ultraviolet light field control system for implementing the foregoing method comprises a laser source, a polarization adjustment system, a beam expansion system, a spatial light modulator, a beam splitter prism, an industrial camera and a computer arranged in sequence along an optical path. The industrial camera is connected to a feedback light path, and the computer is connected to the industrial camera and the spatial light modulator. Through the system, the spot roundness can be improved, and the central intensity of the spot can be more concentrated.

[0065] Also included is a mirror system for sending the laser into the polarization adjustment system. Preferably, the mirror system includes mirror 1 and mirror 2.

[0066] The embodiment of the present application builds an ultraviolet light field regulation system, combines the Gerchberg-Saxton algorithm and the genetic algorithm, uses the Gerchberg-Saxton algorithm to calculate, corrects errors caused by the nonlinear response of the spatial light modulator to the phase mask through the genetic algorithm, and can realize high-quality regulation of the ultraviolet waveband laser using the spatial light modulator in the ultraviolet waveband without gamma correction of the spatial light modulator without special gamma correction.

[0067] The embodiment of the present application does not need to additionally build an optical path to re-correct the value of the gamma curve, greatly improves the usability of the spatial light modulator without gamma correction in the ultraviolet waveband. In addition, since the local optimal value can be found by using the genetic algorithm, this method can be applied in any waveband, and is a scheme with high robustness.

[0068] When the conventional spatial light modulator without gamma correction is applied to the ultraviolet waveband, the optical path is long, the gray value-phase difference is not one-to-one corresponding, and the phase difference is greater than the calibration value. The embodiment of the present application does not need to perform gamma correction on the spatial light modulator, and avoids the nonlinear response of the spatial light modulator in the ultraviolet waveband.

[0069] The above embodiments of the present application are merely examples for clearly illustrating the present application, and are not intended to limit the implementation manners of the present application. Based on the above description, other different forms of changes or modifications can be made by those skilled in the art. Here, all the implementation manners are not required or can not be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for controlling an ultraviolet light field by a complex algorithm driven spatial light modulation without correction space, characterized in that, It comprises the following steps: A. The laser is incident on the spatial light modulator after being expanded and polarized; B. The laser incident on the spatial light modulator is modulated and reflected, and the reflected light is incident on the beam splitter prism, one-way light is incident on the industrial camera as feedback light, and the other way light is output as output light; C. The industrial camera receives the light spot information and uses the Gerchberg-Saxton algorithm to perform preliminary mask calculation in the computer; D. A series of initial populations are generated from the obtained mask, and the genetic algorithm is used to iteratively obtain the optimal phase mask, gradually approaching the optimal solution; F. The spatial light modulator is loaded with the iteratively obtained phase mask to realize the regulation of the ultraviolet band laser light field.

2. The method according to claim 1, wherein, The spatial light modulator is a reflection type spatial light modulator without special gamma correction.

3. The method according to claim 1, wherein, The actual light spot information is obtained by the industrial camera, and the phase mask is calculated by the computer and reloaded into the spatial light modulator to calculate the root mean square error between the actual light spot and the target light spot.

4. The method according to any one of claims 1-3, wherein the method is a method for driving a spatial light modulation of ultraviolet light without correction of space without a spatial light modulation of ultraviolet light with correction. In the Gerchberg-Saxton algorithm, the obtained light spot information is Fourier transformed, the amplitude of the light spot information in the frequency domain is adjusted by adjusting the factor, and the actual frequency position is adjusted by the offset amount adjustment value to realize the one-to-one correspondence of the actual position and actual size of the light spot in the spatial light modulator and the industrial camera.

5. The method according to claim 4, wherein, The adjustment of the amplitude of the light spot information in the frequency domain is expressed as: U 工业相机 [r,s] = Δ 调整 U 空间光调制器 [p,q] where U 工业相机 [r,s] is the amplitude of the frequency domain obtained by the industrial camera, U 空间光调制器 [p,q] is the amplitude of the frequency domain on the spatial light modulator corresponding to the light spot, r,s are the discrete coordinates in space in the industrial camera, p,q are the discrete coordinates in space in the spatial light modulator, Δ 调整 is the adjustment factor.

6. The method according to claim 5, wherein, The expression of the adjustment factor is: where Δx 空间光调制器 is the pixel size of the spatial light modulator, Δx 工业相机 is the pixel size of the industrial camera.

7. The method according to claim 4, wherein, An offset adjustment value x is introduced 调整 and y 调整 to calibrate the pixel of the industrial camera and the spot position of the spatial light modulator, the adjusted relationship is: where Δφ 线性 is the frequency domain offset brought by introducing the offset, in the spatial domain it is actually to move the spot on the industrial camera to the center point, m, n are spatial coordinates, k, l are frequency domain coordinates after Fourier transform.

8. An ultraviolet light field modulation system for implementing the method of any one of claims 1-6, characterized in that, It comprises a laser source, a polarization adjustment system, a beam expansion system, a spatial light modulator, a beam splitter prism, an industrial camera and a computer arranged in sequence along the optical path, the polarization adjustment system is used to adjust the polarization state of the laser, the beam expansion system is used to expand the laser and the expanded light is incident on the spatial light modulator, the spatial light modulator is used to adjust and reflect the incident light, the industrial camera is connected to the feedback light path, and the computer is connected to the industrial camera and the spatial light modulator.

9. The ultraviolet light field regulation system of claim 8, wherein, The polarization adjustment system comprises a polarization beam splitter prism and a half-wave plate, the polarization beam splitter prism is used to obtain linearly polarized light, and the half-wave plate is used to adjust the polarization direction.

10. The ultraviolet light field regulation system of claim 8, wherein, The beam expansion system comprises two plano-convex lenses and a biconvex lens, and the biconvex lens is located between the two plano-convex lenses.

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