Method for seamless image stitching in maskless photoetching
By employing a multi-exposure method involving segmentation and gradually reducing image size, the problems of seam lines and artifacts in image stitching during maskless lithography were solved, achieving seamless image stitching and improving the quality and accuracy of photoresist images.
Patent Information
- Application Number
- CN202511334076.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-18
- Publication Date
- 2025-11-07
AI Technical Summary
When stitching images in maskless lithography, there are problems with seam lines and artifacts, which are costly and unsatisfactory, especially in large-format applications.
By dividing the image to be projected into multiple image subsets and exposing them sequentially to the same position on the photoresist, the image size is gradually reduced, and seamless image stitching is achieved by using multiple exposures, thus eliminating seam lines and artifacts.
Seamless image stitching was achieved, eliminating visible seams and artifacts, and improving the quality and accuracy of photoresist images.
Smart Images
Figure CN120912429A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of image stitching, in particular to a method for seamless image stitching in maskless lithography. BACKGROUND
[0002] Maskless lithography systems are used to project a pattern onto a photoresist material to fabricate microstructures and devices. Creating large area high resolution images requires stitching together many smaller image segments. However, inherent XY positioning errors, especially when the errors are comparable to or exceed the image resolution, such as 1 micron, cause visible seam lines and artifacts between the stitched segments.
[0003] Conventional methods, such as relying on extremely high precision XY positioning systems, are extremely costly, especially for large format applications, such as 400mm x 400mm. Simple linear intensity gradient blending techniques, while alleviating some of the seam issues, introduce artifacts, especially when imaging fine details. These artifacts are due to the modulation transfer function (MTF) of the optical projection system, which causes contrast level variations for different feature sizes, resulting in non-uniform depth profiles in the photoresist. SUMMARY
[0004] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a method for seamless image stitching in maskless lithography, which solves the problem that the prior art cannot eliminate the seam lines and artifacts in the stitched image generated by maskless gray-scale lithography.
[0005] To achieve the above purpose, the present application provides the following solutions:
[0006] A method for seamless image stitching in maskless lithography, comprising:
[0007] obtaining a to-be-projected image;
[0008] segmenting the to-be-projected image to obtain a set of segmented images;
[0009] exposing each image subset in the set of segmented images to the same position of the photoresist in order to obtain a stitched image after exposure.
[0010] Preferably, the image size of each image subset in the set of segmented images decreases in order.
[0011] Preferably, the image size difference of each image subset is any one of 2, 4 or 6 pixels.
[0012] Preferably, the number of each image subset in the set of segmented images is an odd number greater than 3 and less than 17.
[0013] The present application discloses the following technical effects:
[0014] The present application provides a seamless image splicing method in maskless lithography, comprising: obtaining a to-be-projected image; segmenting the to-be-projected image to obtain a segmented image set; exposing each image subset in the segmented image set to the same position of photoresist in sequence to obtain a spliced image after exposure. The present application does not use a simple intensity gradient, but exposes a series of image segments with gradually decreasing sizes to the same position of photoresist in sequence. By using reduced exposure time for each image segment to perform multiple exposures, seamless transition between spliced images is achieved, effectively eliminating visible joint lines and artifacts. BRIEF DESCRIPTION OF DRAWINGS
[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described in the following are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.
[0016] Figure 1 A flow chart of a seamless image splicing method in maskless lithography provided by the present application embodiment;
[0017] Figure 2 Nine image mixing diagrams provided by the present application embodiment. DETAILED DESCRIPTION
[0018] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.
[0019] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.
[0020] As shown in the drawings, the present application provides a seamless image splicing method in maskless lithography, comprising: Figure 1
[0021] Step 100: obtaining a to-be-projected image;
[0022] Step 200: segmenting the to-be-projected image to obtain a segmented image set;
[0023] Step 300: Expose each image subset in the segmented image set to the same position on the photoresist in sequence to obtain the stitched image after exposure.
[0024] Specifically, the stitched image after exposure is not a single image, but an image based on the exposure overlap of the various image subsets.
[0025] For example, consider nine images, each 2 pixels smaller than the previous one. Without blending, the central image would only be exposed for 160 milliseconds. However, by blending and exposing these images sequentially, the exposure time for each image would be approximately 160 / 9 ≈ 17.7 milliseconds.
[0026] We generate and render an image larger than the printable tile size in OpenGL, then print the smaller images sequentially. The black border width between each subsequent image is increased by 2 pixels.
[0027] The final result is: there will be 8 images below the smallest image, resulting in a total of 9 exposures. The edge of the largest image will only have 1 exposure.
[0028] The final result looks the same as normal blending of a single image (blending nine 2-pixel regions from the edge).
[0029] Furthermore, the image sizes of each image subset in the segmented image set decrease sequentially.
[0030] Furthermore, the image size difference between the various image subsets is any one of 2, 4, or 6 pixels.
[0031] Specifically, between each exposure, the width of the black border increases by 2, 4, 6... pixels, with each pixel being approximately 1 micrometer, which determines the horizontal width of the steps.
[0032] Furthermore, the number of each image subset in the segmented image set is an odd number that is greater than 3 and less than 17.
[0033] Specifically, such as Figure 2 As shown, this multi-exposure blending technique uses, for example, nine images, each 2 micrometers smaller than the previous one. Printing all these images in the same location at 1 / 9 of the normal exposure time achieves perfect blending of the small images without any visible artifacts.
[0034] More specifically, the large image is cut into small pieces for printing. These small pieces are typically 400x400 pixels, projected onto a 400x400 micron photoresist emulsion in 180 milliseconds. Instead of a single image, now 9 images are generated. The first image is cut from the large image to be 416x416 pixels, followed by 412x412, 408x408, 404x400, 400x400, 396x396, 392x392, 388x388, and finally 384x384 pixels. Then, each image is projected for 20 milliseconds (180 / 9=20) at the same location on the photoresist emulsion. After exposure, the positioning system moves 400 microns for the next exposure, and the process is repeated. The XY positioning accuracy of the lithography system is better than ±1.5.
[0035] More specifically, the mixing process creates a staircase of intensity distributions, resulting in a depth in the photoresist. The number of images used in the mixing process determines the height of the staircase.
[0036] The total depth of the lithography is between 1.5 and 3 microns.
[0037] If fewer images are used, the staircase height becomes larger: for example, 3 micron depth with 3 images, each corresponding to 1 micron depth.
[0038] If 30 images are used: 3 micron / 30 = 0.1 micron per image.
[0039] Extreme case (300 images): 3 micron / 300 = 0.01 micron per image. This staircase of precision is not measurable and is over-designed.
[0040] Another constraint to consider is the performance of the DMD microdisplay. The minimum exposure time for the display to show a grayscale image is 2.5 milliseconds. If the total exposure time is 160 milliseconds (to reach a 3 micron depth in the photoresist), then a maximum of 160 / 2.5 = 64 images can be used.
[0041] Rules for image size and black border variation:
[0042] Between each exposure, the black border width is increased by 2, 4, 6,... pixels, each pixel being approximately 1 micron, which determines the lateral width of the staircase.
[0043] The number of pixels of the DMD microdisplay is limited (commonly 1920x1080 pixels). If a square tile of 400x400 microns is lithographed, the corresponding image needs to be 400x400 pixels, leaving 1080-400=680 pixels in the vertical direction. If the black border is increased by 4 pixels for each exposure, then the number of images that can be used for mixing is 680 / 4=170. But the image size is also reduced by a factor of 400 / 4=100, and the last image will be completely black.
[0044] The core limitation is the minimum exposure time (2.5 ms) and the total exposure time (160 ms) for the DMD microdisplay to display a full grayscale image, which determines the maximum number of images as 64.
[0045] Common depth range: 0.3 microns to 3 microns.
[0046] The various embodiments are described in the specification in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be mutually referred to.
[0047] The principles and implementation manners of the present application are described by using specific examples in the specification. The above description of the embodiments is only used to help understand the method of the present application and its core idea. Meanwhile, for those skilled in the art, the specific implementation manners and application ranges can be changed according to the idea of the present application. In summary, the content of the specification should not be understood as a limitation of the present application.
Claims
1. A method for seamless image stitching in maskless lithography, characterized in that, The method comprises: acquiring a to-be-projected image; segmenting the to-be-projected image to obtain a segmented image set; exposing each image subset in the segmented image set to the same position of photoresist in sequence to obtain a spliced image after exposure.
2. The method for seamless image stitching in maskless lithography according to claim 1, wherein, The image size of each image subset in the segmented image set is reduced in sequence.
3. The method for seamless image stitching in maskless lithography according to claim 2, wherein, The difference in image size of each image subset is any one of 2, 4 or 6 pixels.
4. The method for seamless image stitching in maskless lithography according to claim 2, wherein, The number of each image subset in the segmented image set is an odd number greater than 3 and less than 17.