A Focusing Method and Device for a Maskless Lithography Machine

Abstract

The present invention relates to the technical field of optical technologies, and particularly relates to a focusing method and device for a maskless lithography machine, including the following steps: S1: Determine the initial position of the displacement stage and collect the light intensity at the initial position; S2: Control the displacement platform to move along the z-axis and collect the light intensity to determine the position when the light intensity reaches the maximum value; S3: Drive the displacement stage to move to a position that is separated from the maximum light intensity by a coarse step size; S4: Use the hill climbing method for rough positioning to determine the approximate position of the focal plane; S5: Fine positioning of the focal plane: Set a fine step size, within ± one coarse step size near the position in step S4, drive the displacement stage to move within this interval according to the length of the fine step size, and obtain the maximum light intensity as P1; S6: Determine the optimal positive focus position: Continue to use the hill climbing method to search for the optimal focus position near the focus, calculate the evaluation function value each time, compare the current calculated value with the database, determine the search direction and step size based on the change of the function value, and efficiently find the positive focus position.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and particularly to a focusing method and device for a maskless lithography machine. Background Art

[0002] Lithography technology, as a key micro-nano processing technology in the semiconductor manufacturing process, is widely used in the fields of integrated circuit (IC) manufacturing, micro-electromechanical systems (MEMS), optoelectronic devices, etc. Traditional lithography machines (including mask lithography machines) usually rely on a mask to project an optical pattern onto a photosensitive material to form the required fine structure. However, as the integrated circuit manufacturing process develops towards smaller nodes, lithography technology faces a series of technical challenges, especially in terms of focusing accuracy, exposure accuracy, and processing speed.

[0003] During the mask lithography process, the focusing error between the mask and the lithography substrate will directly affect the exposure effect, thereby affecting the accuracy and performance of the chip. Therefore, modern lithography machines are usually equipped with high-precision focusing systems to ensure the precise alignment between the mask and the substrate. However, mask lithography machines have certain limitations. Especially in high-resolution lithography, the manufacturing cost of the mask is relatively high, and the requirements for the mask during the lithography process are relatively stringent, which requires more precise focusing technology to improve the lithography quality.

[0004] In recent years, in maskless lithography, instead of using a traditional mask, a digital light source is used to directly write a lithography pattern on a photosensitive substrate. Maskless lithography technology has advantages such as high flexibility, low cost, and suitability for small-batch production. However, maskless lithography technology still faces the problems of how to focus quickly and accurately and reduce the focusing error.

[0005] Therefore, the present application has developed a focusing method and device for a maskless lithography machine to solve the problems existing in the prior art. Summary of the Invention

[0006] The object of the present invention is to provide a focusing method and device for a maskless lithography machine to solve the problems of slow focusing speed in the prior art and the inability to determine which layer the light spot is focused on when focusing on a sample with a multi-layer structure.

[0007] The technical solution of the present invention is: a focusing method for a maskless lithography machine, comprising the following steps:

[0008] S1: Determine the initial position of the displacement stage and collect the light intensity at the initial position: Determine the total length L in the z-axis direction of the displacement stage. When the displacement stage is not at the initial position, drive the displacement stage to move to the initial position;

[0009] S2: Control the displacement stage to move along the z-axis and collect the light intensity to determine the position at which the maximum light intensity is obtained;

[0010] S3: Drive the displacement stage to move to a position that is one coarse step away from the maximum light intensity;

[0011] S4: On the basis of the coarse positioning in S3, use the hill climbing method to compare the light intensity value or image sharpness to determine the approximate position of the focal plane;

[0012] S5: Fine positioning of the focal plane: Set a fine step size, within ± one coarse step size near the position in step S4. Drive the displacement stage to move within this interval according to the length of the fine step size and obtain the maximum light intensity as P1;

[0013] S6: Determine the optimal ortho-focus position: Continue to use the hill climbing method to search for the optimal focus position near the focus, calculate the evaluation function value each time, compare the current calculated value with the database, determine the search direction and step size based on the change of the function value, and efficiently search for the ortho-focus position.

[0014] Preferably, step S2 includes the following steps:

[0015] S2.1: Set a coarse step size;

[0016] S2.2: The displacement stage moves along the z-axis direction according to the length of the coarse step size, and collect the light intensity of each step until the moving distance l = L, and collect the maximum light intensity P during the movement.

[0017] Preferably, step S4 includes the following steps:

[0018] S4.1: Collect the image and denoise the image: Collect the original lithography image and use an adaptive function to adjust the brightness and contrast of the image, and use Gaussian filtering and median filtering on the gray-scale processed image to remove the noise of the image;

[0019] S4.2: Calculate the gradient values of the image in four directions and take the extreme difference value;

[0020] S4.3: Perform edge suppression processing and morphological processing on the image, judge whether the current position of the image is the ortho-focus position, and determine the approximate position of the focal plane.

[0021] Preferably, in step S4.2, calculate the gradient values of the image in the four directions of horizontal, vertical, 45 degrees, and 135 degrees through an edge gradient operator, and obtain the difference between the maximum and minimum values of the gradients in the four directions as the gradient value.

[0022] A maskless lithography apparatus, comprising: a DMD chip, an imaging device, a focusing device, and a displacement stage. A substrate to be processed is placed on the displacement stage. The image on the DMD chip is reflected multiple times by the imaging device and then imaged on the substrate to be processed. The focusing device includes a laser light source, a beam splitting unit, and a photomultiplier tube. The beam splitting unit is located in the emission direction of the laser light source, and the laser is reflected by the beam splitting unit onto the substrate to be processed. After being reflected by the substrate to be processed, the laser is received by the photomultiplier tube.

[0023] Preferably, the imaging device includes an LED light source, a reflecting prism, a first reflector, a second reflector, and an eyepiece. The reflecting prism is located in the irradiation direction of the LED light source, and the DMD chip is located in the reflection direction of the reflecting prism. The image of the DMD chip is reflected by the first reflector and the second reflector through the reflecting prism, passes through the eyepiece, and is imaged on the substrate to be processed. Both the first reflector and the second reflector make the reflected light present a 90-degree reflection.

[0024] Preferably, the beam splitting unit includes a first beam splitter, a second beam splitter, a third reflector, and a beam splitting prism. The beam splitting prism is located between the first reflector and the second reflector. The laser light source emits laser, which successively passes through the first beam splitter, the second beam splitter, the third reflector, and the beam splitting prism, and the laser is reflected onto the second reflector. The photomultiplier tube is located in the reflection direction of the second beam splitter.

[0025] Preferably, the beam splitting prism is also provided with a dust cover.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] (1) The magnitude of the light intensity at different times is quickly collected by the photomultiplier tube and compared, and the maximum light intensity is selected to preliminarily determine the best focal plane. Then, the image processing is performed at the best focal plane position by the hill climbing method to preliminarily determine the focal point position. The displacement stage moves with a small step size near the focal point, and the photomultiplier tube captures the maximum light intensity again. The two light intensities are compared to determine the focal point position at this time. The data near the focal point at this time is calculated again by the hill climbing method to obtain the focal point position. The initial focal plane position is quickly determined by the magnitude of the light intensity, and the focal point position is further determined by the hill climbing method, reducing the complex process of image processing and also overcoming the problem of determining the best focal point position when the multi-layer structure cannot be determined by the light intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below in conjunction with the drawings and embodiments:

[0029] Figure 1 It is a flowchart of the focusing method of a maskless lithography machine according to the present invention;

[0030] Figure 2 It is a schematic structural diagram of a maskless lithography machine device according to the present invention;

[0031] Figure 3 It is a top view of a maskless lithography machine device according to the present invention;

[0032] Figure 4 It is a Gamma curve graph of the adaptive function of the present invention;

[0033] Figure 5 It is a schematic diagram of the hill climbing method search of the present invention;

[0034] Figure 6 It is a schematic diagram of the principle of Gaussian filtering for processing images of the present invention;

[0035] Figure 7 It is a diagram of the median filtering calculation process in the present invention.

[0036] Wherein: 1. DMD chip; 2. Imaging device; 21. LED light source; 22. Reflective prism; 23. First reflector; 24. Second reflector; 25. Eyepiece; 3. Focusing device; 31. Laser light source; 32. Beam splitting part; 321. First beam splitter; 322. Second beam splitter; 323. Third reflector; 324. Beam splitting prism; 325. Dust cover; 33. Photomultiplier tube; 4. Displacement stage. Detailed implementation manners

[0037] The following combines specific embodiments to further elaborate on the content of the present invention:

[0038] As Figures 1-3 shown, a focusing method for a maskless lithography machine includes the following steps:

[0039] S1: Determine the initial position of the displacement stage 4 and collect the light intensity at the initial position: Determine the total length L of the displacement stage 4 in the z-axis direction. When the displacement stage 4 is not at the initial position, drive the displacement stage 4 to move to the initial position. The displacement stage 4 returning to the initial position can ensure the precise alignment and overlay of the lithography pattern with a specific position on the substrate, thereby improving the position accuracy of the lithography pattern and ensuring the uniformity and stability of the light intensity at the position during exposure. By returning to the initial position, a consistent light intensity distribution can be obtained during each exposure, thereby improving the quality and consistency of the lithography pattern.

[0040] S2: Control the displacement platform to move on the z-axis and collect the light intensity to determine the position when the light intensity reaches the maximum value;

[0041] S2.1: Set a coarse step size. Specifically, the coarse step size is between 0.1 μm and 1 μm. The setting of the coarse step size is mainly to quickly approach the best focus position during the focusing process. Since the focusing range of the lithography machine may be relatively large, the coarse step size can rapidly reduce the gap with the best focus position at the initial stage of focusing, thereby laying the foundation for the subsequent fine focusing steps, significantly reducing the time required to reach the preliminary focusing state, and thus improving the production efficiency of the entire lithography process;

[0042] S2.2: The displacement stage 4 moves along the z-axis direction by the length of the coarse step size, and collects the light intensity of each step until the moving distance l = L, and collects the maximum light intensity P1 during the moving process;

[0043] After the displacement stage 4 moves to the initial position, turn on the laser light source 31 and irradiate the first beam splitter 321. After the laser is reflected by the first beam splitter 321, the second beam splitter 322, the third reflector 323 and the beam splitting prism 324, the laser is reflected to the second reflector 24 and then reflected again through the eyepiece 25, and the laser is hit on the substrate to be processed. The laser is reflected again by the substrate to be processed, and successively passes through the eyepiece 25, the second reflector 24, the beam splitting prism 324, the third reflector 323 and the second beam splitter 322. The reflected laser is reflected by the second beam splitter 322 to the photomultiplier tube 33, and the photomultiplier tube 33 collects the light intensity at this time. The photomultiplier tube 33 collects the light intensity at the current position every other coarse step size. When the moving distance l = L of the displacement stage 4 in the z-axis direction is reached, the light intensity collection on the z-axis path is completed, and the maximum light intensity value P is recorded.

[0044] Further, the beam splitting prism 324 is provided with a dust cover 325, and the dust cover 325 can effectively prevent dust and dirt from adhering to the surface of the beam splitting prism 324, thereby maintaining the stability and accuracy of its optical performance, and improving the accuracy and accuracy of measurement.

[0045] S3: Drive the displacement stage 4 to move to a position one coarse step size away from the maximum light intensity. After determining the position of the maximum light intensity, the approximate position of the focal plane is initially determined. By finding the position of the maximum light intensity and moving one coarse step size on this basis, the relative position between the lithography machine lens and the silicon wafer can be initially determined, providing a general reference point for subsequent finer focusing adjustments. If the displacement stage 4 is directly moved to the maximum light intensity position, it may cause over-focusing, that is, the distance between the lens and the substrate to be processed is too close, resulting in image distortion or damage during exposure. Moving one coarse step size can effectively avoid this risk, and at the same time can rapidly reduce the focusing range, enabling subsequent finer focusing adjustments to be carried out faster, thereby improving the overall focusing efficiency.

[0046] In this embodiment, the focal plane is initially determined by comparing the light intensity and the degree of focus. Since there is a clear corresponding relationship between the change in light intensity and the focusing state, the best focus point can be found relatively accurately. Moreover, the response speed of light intensity focusing is usually fast, and complex image processing algorithms are not required, which helps to shorten the focusing time and improve production efficiency. However, when imaging the DMD chip 1, the spot area covered by laser focusing is large. For imaging without an image, light intensity can be used for rapid focusing. For imaging with an image, the spot will cover multiple layers of structures, and it is impossible to determine which layer the focus is on. Therefore, focusing only by light intensity cannot meet the focusing requirements, so image processing needs to be added to determine the focusing position.

[0047] S4: Use the hill-climbing method for rough positioning to determine the approximate position of the focal plane. The hill-climbing method gradually approaches the best focusing position by comparing the light intensity or the evaluation function values at different positions, and can quickly narrow the search range during the rough positioning stage.

[0048] S4.1: Collect the image and denoise the image: Collect the original lithography image and use the adaptive function to adjust the brightness and contrast of the image, and process the gray-scale image with Gaussian filtering and median filtering to remove the noise in the image. The adaptive function can dynamically adjust the brightness and contrast according to the local features of the image, making the details in the image clearer, the contrast more distinct, improving the visual effect of the image, making the lithography structure easier to observe and identify, and at the same time improving the accuracy and efficiency of subsequent image processing, because the enhanced image can provide more useful information.

[0049] Specifically, in the image preprocessing stage, the Gamma adaptive function is selected, and Gamma correction is used to adjust the brightness and contrast of the image. Gamma correction originates from the response curve of the CRT monitor, that is, the non-linear relationship between its brightness and the input voltage. Its working principle is to edit the Gamma curve of the image, perform non-linear tone adjustment on the image, find the dark and bright parts in the image signal, and increase the ratio between them, expanding the dynamic range of the image and improving the effect of image contrast.

[0050] Gamma correction can be implemented through simple operations, that is, by performing function transformation on the gray values of the image. Its standard form in image processing is as follows:

[0051]

[0052] Among them, S represents the pixel value after transformation, and R represents the original image pixel value mapped to [0, 1]. As a control parameter in the transformation process, it plays a key role in the image enhancement algorithm based on Gamma correction. It determines the final adjustment effect of brightness and contrast.

[0053] For a frame of image in a reasonable state, the average value of all pixels after normalization is roughly around 0.5. In the process of adaptive gamma correction, there is the following corresponding relationship between the γ value and the average brightness X of the image:

[0054]

[0055] From the above formula, when the mapping range of the brightness average value X is [0,1], the corresponding γ∈ [0.130288,2.847366], according to the size of γ, the corresponding Gamma curve is obtained as follows Figure 4 As shown, according to Figure 4 The relationship diagram dynamically and adaptively adjusts brightness and contrast.

[0056] Among them, Gaussian filtering is a linear filtering technology that smoothes the image through a Gaussian function. Figure 6 As shown in the figure, the core of the method is to create a Gaussian kernel whose central value is the largest and the surrounding values gradually decrease. During filtering, this Gaussian kernel is slid on the image, the weighted average of the pixels in the kernel is calculated, and then the value of the pixel in the center of the kernel is replaced by this value. This can effectively remove high-frequency noise while retaining low-frequency image details.

[0057] The median filter is an effective image processing technique that updates the grayscale value of each pixel by calculating the median of all the pixel grayscale values in its specific neighborhood. This process makes the surrounding pixel values closer to the actual situation, thereby effectively eliminating isolated noise points and having a significant filtering effect on impulse noise. More importantly, while removing noise, the median filter can well protect the edge and detail information of the image, preventing the image from becoming blurred due to filtering. Its calculation process is as follows: Figure 7 As shown: a window containing five points is selected, and then the pixels in the window are scanned one by one, the grayscale values corresponding to each pixel are arranged in ascending or descending order, and finally the middle value is selected to replace the grayscale value of the pixel.

[0058] In actual application, there are many different shapes of windows to choose from in the median filtering process, such as square, cross, ring and circle. These windows of different shapes will bring different filtering effects in the application. For example, square and circular windows are more suitable for processing images with long outer edges due to their shape characteristics; while cross-shaped windows perform well in processing images with sharp corners due to their structural characteristics. Figure 7As shown, a rectangular window is selected in this application because the rectangular window processes pixel values evenly in all directions, can effectively smooth the image, and can better retain edge information at the same time.

[0059] S4.2: Calculate the gradient values of the image in four directions and take the extreme difference value. Calculate the gradient values of the image in the horizontal, vertical, 45-degree, and 135-degree directions through the edge gradient operator, and obtain the difference between the maximum and minimum gradient values in the four directions as the gradient value. Calculating the gradient value can highlight the edge features in the image because the edge is the area where the gray value changes most violently. By comparing the gradient values in the four directions, the intensity and direction of the edge can be determined. By calculating the gradient values in the four directions and taking the extreme difference value, richer image feature information can be obtained, which helps to more accurately adjust the focusing position, so that the lithography image reaches the best focusing effect, thereby reducing the error rate.

[0060] S4.3: Perform edge suppression processing and morphological processing on the image, judge whether the current position of the image is the in-focus position, and determine the approximate position of the focal plane. Edge suppression processing can reduce or eliminate the edge effect in the image, thereby reducing factors such as noise and lens distortion caused during the image acquisition process. Through edge suppression, the edges in the image can be made smoother, reducing the focusing error caused by the edge effect. Morphological processing can be used to further smooth the image, highlight the key features in the image, and reduce the interference of noise, which helps to more accurately judge whether the current position of the image is the in-focus position, thereby improving the focusing accuracy.

[0061] S5: Fine positioning of the focal plane: Set a fine step size. Specifically, the fine step size is between 0nm - 10nm. Through the further refinement after focusing with the coarse step size, it is ensured that the lithography machine can meet the final focusing accuracy requirements. Since the lithography process has extremely high requirements for accuracy, the fine step size can perform fine adjustment in the final stage of focusing, thereby maximizing the focusing accuracy. It can ensure that after the lithography machine reaches the preliminary focusing position, it continues to make small adjustments to meet the final focusing accuracy requirements, within ± one coarse step size near step S4. Drive the displacement stage 4 to move in this interval according to the length of the fine step size, and obtain the maximum light intensity as P1. When performing fine positioning, collect the light intensity every other fine step size and determine the maximum light intensity P1. When P1 > P, the displacement stage 4 moves to the position where P1 is located to achieve fast focusing for fine positioning. Through the movement of the displacement stage 4, the light intensity within the interval can be collected quickly, and further shorten the time for the focus point, improving work efficiency. After focusing on the product to be detected, it is necessary to replace the product to be detected, and the product to be detected can be replaced frequently and quickly at the same time.

[0062] S6: Determine the optimal in-focus position: Near the focus, continue to use the hill-climbing method to search for the optimal focus position, calculate the evaluation function value each time, compare the current calculated value with the database, determine the search direction and step size based on the change in the function value, and efficiently search for the in-focus position. Move the displacement stage 4 according to the result of the hill-climbing method. If the function value of the hill-climbing method increases, drive the displacement stage 4 to continue moving forward; if it decreases, reverse the direction and reduce the step size. When a peak appears, reverse the direction at the corresponding position and reduce the step size to continue the search until the position where the maximum value of the comprehensive evaluation function is found. Through the acquisition of the maximum light intensity twice, the data for image processing is greatly reduced, and the focus position can be determined quickly and accurately.

[0063] In this embodiment, the evaluation function in steps S4 and S6 selects the PMBG focusing evaluation function, and its calculation formula is as follows:

[0064] ;

[0065] ;

[0066] : The selected direction angle;

[0067] M, N: Respectively represent the row and column of the pixel;

[0068] : The value of the corresponding pixel point;

[0069] : The gradient of the corresponding pixel point;

[0070] : The general expression of the convolution matrix of the Brenner operator.

[0071] Among them, 。

[0072] The accuracy of the autofocus system is significantly improved by the PMBG focus evaluation function. Whether the focus is clear is judged by calculating the gradient value. The PMBG focus evaluation function is selected based on the following advantages: First, the visual characteristics of the human eye are fully considered. Since the human vision is more sensitive to green, the data of the green channel is used as the input. This can not only ensure the effective acquisition of image edge information, but also well take into account the evaluation of the focus degree of the image by the human eye, while greatly reducing the computational complexity. Second, improvements are made at the operator level. The Brenner operator in the PMBG focus evaluation function is extended, changing it from two directions in one horizontal direction to eight directions originally, and the gradient operators in four directions of 0°, 45°, 90°, and 135° are selected from them. The focus evaluation function value is determined by multiplying and summing the gradient values in these four directions, which greatly enlarges the function value gap between the focused image and the slightly defocused image, significantly enhances the resolution ability of images with different focus degrees, and thus obtains a more excellent clarity ratio and sensitivity factor.

[0073] Specifically, the hill climbing method simulates the process of a climber looking for a mountain peak, continuously selects better solutions, and thus gradually approaches the optimal solution of the problem. Its basic principle is to continuously select the solution that makes the objective function value the largest (or smallest) in the neighborhood, and gradually approach the local optimal solution until reaching a local highest point (or lowest point) or no higher point (or lower point) can be found. In this process, the function value is used as the standard to measure the quality of the solution, guiding the search direction. In the hill climbing method, the function value is usually calculated by a pre-defined evaluation function, that is, the function value of the hill climbing method is the evaluation function value.

[0074] As Figure 5 shown, first start from the starting position with a large step size, compare the size of the focus evaluation function values of the previous and current frames and determine the forward direction of the next step. If the value of the previous frame is less than the current frame, continue to move in this direction; if the value of the previous frame is greater than the current frame, reverse the rotation of the motor. After determining the rotation direction of the zoom motor, still search with a large step size, rotate from point A towards point B until the curve trend is downward, that is, the focus evaluation function value of the current frame is less than that of the previous frame. The large step size causes the positive focus position to be missed. If the value at point B is less than that at point F, continue to rotate in the same direction. If the value at point F is greater than that at point H, it indicates that the focus evaluation function curve trend is downward. At this time, change the rotation direction of the zoom motor and reduce the search step size. When the value of the previous frame is less than the current frame again, that is, the value at point C is less than that at point G, change the rotation direction of the zoom motor and reduce the search step size again. Repeat the above steps repeatedly until the search step size is the minimum step size, and the peak point E of the focus evaluation function curve is found with the minimum step size, which indicates that the autofocus is successful.

[0075] A maskless lithography apparatus is controlled by a focusing method of a maskless lithography machine, and includes a DMD chip 1, an imaging device 2, a focusing device 3, and a displacement stage 4. A substrate to be processed is placed on the displacement stage 4. The imaging device 2 includes an LED light source 21, a reflecting prism 22, a first reflecting mirror 23, a second reflecting mirror 24, and an eyepiece 25. The focusing device 3 includes a laser light source 31, a beam splitting unit 32, and a photomultiplier tube 33. The LED light irradiates the image on the DMD chip 1 and reflects it to the substrate to be processed through the imaging device 2. The laser light source 31 emits laser light, and the laser light is irradiated on the photomultiplier tube 33 through the beam splitting unit 32 to obtain the light intensity, thereby preliminarily determining the focusing position.

[0076] Furthermore, both the first reflecting mirror 23 and the second reflecting mirror 24 make the reflected light present a 90-degree reflection. The 90-degree reflection makes the light propagation in the lithography machine more stable, reduces the errors caused by light deflection or scattering, thereby improving the lithography accuracy. At the same time, it also arranges the optical elements and mechanical structures inside the lithography machine more flexibly, making the spatial layout of the entire system more compact and reasonable.

[0077] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims within the present invention.

Claims

1. A focusing method for a maskless lithography machine, characterized in that, It includes the following steps: S1: Determine the initial position of the displacement stage (4) and collect the light intensity at the initial position: Determine the total length L of the displacement stage (4) in the z-axis direction. When the displacement stage (4) is not at the initial position, drive the displacement stage (4) to move to the initial position; S2: Control the displacement stage to move along the z-axis and collect the light intensity to determine the position when the light intensity reaches the maximum value; S2.1: Set a coarse step size; S2.2: The displacement stage (4) moves along the z-axis direction by the length of the coarse step size, and collect the light intensity of each step until the moving distance l = L, and collect the maximum light intensity P during the movement; S3: Drive the displacement stage (4) to move to a position one coarse step size away from the maximum light intensity; S4: On the basis of the coarse positioning in S3, use the hill climbing method to compare the light intensity value or image sharpness to determine the approximate position of the focal plane; S5: Fine positioning of the focal plane: Set a fine step size, within ± one coarse step size near the position in step S4, drive the displacement stage (4) to move in this interval by the length of the fine step size, and obtain the maximum light intensity as P1; S6: Determine the optimal ortho-focus position: Continue to use the hill climbing method near the focus to search for the optimal focus position, calculate the evaluation function value each time, compare the current calculated value with the database, and determine the search direction and step size based on the change of the function value to efficiently find the ortho-focus position.

2. The focusing method of a maskless lithography machine according to claim 1, characterized in that: Step S4 includes the following steps: S4.1: Collect the image and denoise the image: Collect the original lithography image and use the adaptive function to adjust the brightness and contrast of the image, and use Gaussian filtering and median filtering to process the gray-scale image to remove the noise of the image; S4.2: Calculate the gradient values of the image in four directions and take the extreme difference value; S4.3: Perform edge suppression processing and morphological processing on the image, judge whether the current position of the image is the ortho-focus position, and determine the approximate position of the focal plane.

3. The focusing method of a maskless lithography machine according to claim 2, characterized in that: In step S4.2, calculate the gradient values of the image in four directions of horizontal, vertical, 45 degrees and 135 degrees through the edge gradient operator, and obtain the difference between the maximum and minimum values of the gradients in the four directions as the gradient value.

4. A maskless lithography machine device, which is controlled by using the focusing method of a maskless lithography machine according to any one of claims 1-3, characterized in that, It includes: DMD chip (1), imaging device (2), focusing device (3) and displacement stage (4). The substrate to be processed is placed on the displacement stage (4). The image on the DMD chip (1) is reflected multiple times by the imaging device (2) and imaged on the substrate to be processed. The focusing device (3) includes a laser light source (31), a beam splitting part (32) and a photomultiplier tube (33). The beam splitting part (32) is located in the emission direction of the laser light source (31), and the laser is reflected to the substrate to be processed through the beam splitting part (32). After the laser is reflected by the substrate to be processed, it is received by the photomultiplier tube (33).

5. The maskless lithography apparatus according to claim 4, characterized in that: The imaging device (2) includes an LED light source (21), a reflecting prism (22), a first reflecting mirror (23), a second reflecting mirror (24), and an eyepiece (25). The reflecting prism is located in the irradiation direction of the LED light source (21), and the DMD chip (1) is located in the reflection direction of the reflecting prism (22). The reflecting prism (22) reflects the image of the DMD chip (1) through the first reflecting mirror (23) and the second reflecting mirror (24), and passes through the eyepiece (25) to form an image on the substrate to be processed. Both the first reflecting mirror (23) and the second reflecting mirror (24) reflect the reflected light at a 90-degree angle.

6. The maskless lithography apparatus according to claim 5, characterized in that: The beam splitting unit (32) includes a first beam splitter (321), a second beam splitter (322), a third reflecting mirror (323), and a beam splitting prism (324). The beam splitting prism (324) is located between the first reflecting mirror (23) and the second reflecting mirror (24). The laser light source (31) emits laser light, which sequentially passes through the first beam splitter (321), the second beam splitter (322), the third reflecting mirror (323), and the beam splitting prism (324), and reflects the laser light to the second reflecting mirror (24). The photomultiplier tube (33) is located in the reflection direction of the second beam splitter (322).

7. The maskless lithography apparatus according to claim 6, wherein: The beam splitting prism (324) is also provided with a dust cover (325).

Images