Lithographic alignment mark pattern structure supporting assisted focus
By combining cross-shaped and square-shaped MTF target patterns into the photolithographic alignment mark pattern structure, the problem of low accuracy in mark coordinate calculation was solved, improving focusing and alignment accuracy and simplifying the consistency adjustment of the processing technology.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- ZHIFENGQI (SUZHOU) OPTOELECTRONICS TECHNOLOGY CO LTD
- Filing Date
- 2025-09-10
- Publication Date
- 2026-06-26
Smart Images
Figure CN224417168U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a semiconductor photolithography processing technology, specifically to an alignment mark pattern structure for semiconductor photolithography processing that simultaneously supports auxiliary focusing. Background Technology
[0002] In semiconductor processing technologies involving geometric tolerances, such as photolithography, bonding, and flip-chip bonding, alignment techniques based on graphic markings are commonly used. This involves using a microscopic imaging module to acquire images of specific markings on the current and previous layers, calculating the coordinate positions of the markings, and providing the motion mechanism with instructions to make their coordinates consistent by calculating the coordinate differences between the current and previous markings. By controlling the coordinate differences within the error window, alignment is achieved.
[0003] Under the current technological system, the most commonly used markings are crosses, squares, or grids, such as... Figure 1 As shown, the left image depicts a large cross within a smaller cross structure, while the right image shows a combination of squares within a cross structure. The black and gray areas are used to mark the current and previous layers, respectively. Simple symmetrical patterns, especially cross shapes, facilitate high-precision calculation of geometric center coordinates. However, considering various random factors during equipment operation, the possibility of poor focusing quality cannot be ruled out, affecting coordinate calculation accuracy and consequently alignment accuracy. Because simple patterns are relatively insensitive to defocusing and difficult to quantify, focusing efficiency and alignment accuracy may be affected simultaneously.
[0004] To improve focusing accuracy, existing technologies typically use a separate MTF target. However, MTF targets are difficult to extract quickly. Therefore, existing technologies require two sets of marker patterns, one for focus adjustment and the other for coordinate position extraction. The subsequent positioning and adjustment after coordinate position extraction can affect the focusing process, thus increasing the difficulty of adjusting alignment and focus accuracy and slowing down the adjustment speed.
[0005] Therefore, how to ensure the accuracy of the marker coordinate calculation, while quantitatively ensuring the focusing and imaging quality and improving the consistency of the processing technology, is a problem that needs to be solved in this field. Summary of the Invention
[0006] The purpose of this invention is to provide a photolithographic alignment mark pattern structure that supports auxiliary focusing, enabling rapid quantitative evaluation and confirmation of the imaging focal plane of the alignment system during semiconductor overlay processes or testing, thereby improving the accuracy and repeatability of mark position calculation.
[0007] To achieve the above-mentioned objectives, the technical solution adopted by this utility model is as follows: a photolithographic alignment mark pattern structure that supports auxiliary focusing, having a cross-shaped first alignment mark main pattern and four square second alignment mark main patterns respectively nested in the four quadrants of the cross shape, with a first MTF target pattern provided at each of the four ends of the cross shape of the first alignment mark main pattern, and a set of second MTF target patterns provided at the outer corners of the four squares of the second alignment mark main pattern.
[0008] In the above technical solution, the first alignment mark main pattern and the first MTF target pattern can be regarded as layer A. MTF grid targets are equipped at the four ends of the crosshair, allowing the acquisition of MTF at four symmetrically distributed positions in the image. When all targets reach their optimal state, the focal plane of the current layer's imaging is ensured to be in the optimal state. The directions of the four MTF targets include two sets of horizontal and two sets of vertical directions, which can eliminate the influence of astigmatism. The second alignment mark main pattern and the second MTF target pattern can be regarded as layer B. MTF grid targets are equipped on the outer side of a single corner of the square main pattern, with each set containing one horizontal and one vertical grid, which can eliminate the influence of astigmatism. Arranging the four sets of MTF grid targets symmetrically allows the acquisition of MTF at four symmetrically distributed positions in the image. When all targets reach their optimal state, the focal plane of the current layer's imaging is ensured to be in the optimal state. Layers A and B can be arbitrarily used as the current or previous layer patterns to accommodate the convenient testing requirements of multi-layer overlay.
[0009] In the above technical solution, the first MTF target pattern is a grid pattern, and the stripe direction of the grid is parallel to the width direction of the end of the cross-shaped pattern.
[0010] In a preferred embodiment, the total length of the horizontal bars in the cross shape is equal to the total length of the vertical bars, and they intersect at their respective midpoints to form a centrally symmetrical structure. The geometric centers of the first MTF target patterns at the four ends of the cross shape are located on the central symmetry axis of the cross shape. At the same time, the structure of each first MTF target is also centrally symmetrical about the central symmetry point of the cross shape.
[0011] In the above technical solution, the second MTF target pattern is composed of two mutually perpendicular grid patterns, and the two grid patterns are respectively located on the outer sides of the two sides forming the outer corner of the square.
[0012] In a preferred embodiment, the stripe direction of each grid is arranged perpendicular to the direction of the edge of the square it belongs to.
[0013] In a preferred embodiment, the spatial resolution corresponding to a single pixel of the alignment camera is denoted as d, and all feature sizes of the first alignment mark main pattern, the second alignment mark main pattern, the first MTF target pattern, and the second MTF target pattern are integer multiples of d.
[0014] The MTF grid width does not exceed 4d.
[0015] More preferably, the MTF grid width is d.
[0016] Due to the application of the above technical solution, this utility model has the following advantages compared with the prior art:
[0017] 1. This utility model adds an MTF target to the outer end of a common alignment mark, which enables rapid quantitative evaluation of the alignment mark's imaging quality, helps ensure that the mark image is acquired in the best condition, and then calculates the coordinates of the mark's location with higher accuracy.
[0018] 2. In this utility model, focal plane calibration and position calculation can be completed continuously and automatically.
[0019] 3. Through structural settings, the MTF target and the traditional pattern are both interconnected and relatively independent, without affecting the use of the original alignment algorithm.
[0020] 4. The layer and the preceding layer can exchange definitions in practical applications and are compatible with each other. Attached Figure Description
[0021] Figure 1 This is a schematic diagram of alignment marks in the prior art;
[0022] Figure 2 This is a schematic diagram of the marking structure according to an embodiment of the present utility model;
[0023] Figure 3 yes Figure 2 A magnified view of a section of 102;
[0024] Figure 4 yes Figure 2 A magnified view of a section of section 202;
[0025] Figure 5 This is a schematic diagram of the A-layer baseline used in the embodiment;
[0026] Figure 6 This is a schematic diagram of the B-layer baseline used in the embodiment. Detailed Implementation
[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments:
[0028] Example 1: See Figure 2As shown, a photolithographic alignment mark pattern structure supporting assisted focusing has a cross-shaped first alignment mark main pattern 101 and four square second alignment mark main patterns 201 respectively nested in the four quadrants of the cross shape. A first MTF target pattern 102 is provided at each of the four ends of the cross shape of the first alignment mark main pattern 101, and a set of second MTF target patterns 202 is provided at each of the four squares of the second alignment mark main pattern 201.
[0029] The first alignment mark main pattern 101 and the first MTF target pattern 102 are combined into one layer, called layer A. The second alignment mark main pattern 201 and the second MTF target pattern 202 are combined into one layer, called layer B.
[0030] In layer A, the cross-shaped structure is centrally symmetrical. MTF grid targets are placed at the four ends of the cross, allowing the acquisition of MTF at four symmetrically distributed positions in the image. When all targets are at their optimal state, it ensures that the focal plane of the layer is in its optimal state. The four MTF targets have two sets of horizontal and two sets of vertical orientations, which can eliminate the effects of astigmatism. See also Figure 3 The first MTF target pattern 102 is a grid pattern, and the direction of the grid stripes is parallel to the width direction of the end of the cross-shaped pattern.
[0031] In layer B, the squares also form a centrally symmetrical structure with a cross-shaped center. MTF grid targets are placed on the outer side of each corner of the main square pattern, with each group containing one horizontal and one vertical grid to eliminate astigmatism. Four groups of MTF grid targets are arranged symmetrically to acquire the MTF at four symmetrically distributed positions in the image. When all targets are at their optimal state, it ensures that the focal plane of the layer is at its best. See also... Figure 4 The second MTF target pattern 202 consists of a set of two mutually perpendicular grid patterns. The two grid patterns are located on the outer sides of the two sides forming the outer corners of the square, and the stripe direction of each grid is arranged perpendicular to the direction of the side of the square.
[0032] The spatial resolution corresponding to a single pixel of the alignment camera is denoted as d. All feature dimensions of the first alignment mark main pattern, the second alignment mark main pattern, the first MTF target pattern, and the second MTF target pattern are integer multiples of d. In this embodiment, the F grid width is preferably d.
[0033] The preliminary work for the corresponding alignment marks and operation method system is as follows:
[0034] 1. Confirm the compatibility between the MTF grid size and the resolution parameters of the aligned camera;
[0035] 2. Calibrate the relationship curve between the defocus amount of the camera focal plane and the measured MTF.
[0036] Based on the above preparations, the process for using the cross markers on layer A is as follows:
[0037] 1. Based on the X and Y coordinate values obtained from the pre-alignment, bring the alignment mark pattern into the field of view of the alignment camera;
[0038] 2. Adjust the Z-axis coordinate of the platform to achieve a preliminary clear image contrast;
[0039] 3. See appendix Figure 5 As shown, calculate the row and column numbers of the two baselines 103 and 104, and perform θ-axis adjustment if necessary to ensure that the mark is parallel to the camera pixels; where θ-axis adjustment refers to rotating around the vertically upward axis;
[0040] 4. Read the grayscale curve corresponding to row 103, and fine-tune the X-axis of the platform to make the curve symmetrical;
[0041] 5. Read the grayscale curve of the corresponding column 104, and fine-tune the Y-axis of the platform to make the curve symmetrical;
[0042] 6. Calculate the MTF values of the four 102 markers. If the grid width is d, directly take the grayscale value of a single pixel. If it is n times d, merge the grayscale values of every n pixels. The grayscale values of bright areas are denoted as "DN bright", and the grayscale values of dark areas are denoted as "DN dark". The MTF calculation formula is:
[0043] (π / 4)*(DN bright-DN dark) / (DN bright+DN dark)
[0044] 7. If the MTF of all four markers is consistent with the optimal state obtained during calibration, then it is confirmed that it is in the optimal state. If it is lower than the optimal MTF value, adjust the Z-axis elevation and, if necessary, adjust the pitch until the optimal state is reached.
[0045] 8. Calculate the center position of the cross mark.
[0046] Based on the above preparations, the process for using the B-layer combined block marker is as follows:
[0047] 1. Based on the X and Y coordinate values obtained from the pre-alignment, bring the alignment mark pattern into the field of view of the alignment camera;
[0048] 2. Adjust the Z-axis coordinate of the platform to achieve a preliminary clear image contrast;
[0049] 3. See appendix Figure 6 Calculate the row and column numbers of the four baselines 203, 204, 205, and 206, and perform θ-axis adjustment if necessary to ensure that the marks are parallel to the pixels of the aligned camera.
[0050] 4. Read the grayscale curve corresponding to row 203, and fine-tune the X-axis of the platform to make the curve symmetrical. If the state of 204 is different from that of 203, adjust the θ-axis to further improve the parallelism between the marker and the camera pixel.
[0051] 5. Read the grayscale curve corresponding to column 205, fine-tune the Y-axis of the platform to make the curve symmetrical. If the state of 206 is different from that of 205, adjust the θ-axis to further improve the parallelism between the marker and the aligned camera pixels.
[0052] 6. Calculate the MTF value of the eight 202 markers. If the grid width is d, directly take the grayscale value of a single pixel. If it is n times d, merge the grayscale values of every n pixels. The grayscale value of the bright area is recorded as "DN bright", and the grayscale value of the dark area is recorded as "DN dark". The MTF calculation formula is:
[0053] (π / 4)*(DN bright-DN dark) / (DN bright+DN dark)
[0054] 7. If the MTF of all four sets of markers is consistent with the optimal state obtained during calibration, then it is confirmed that it is in the optimal state. If it is lower than the optimal MTF value, adjust the Z-axis elevation and, if necessary, adjust the pitch until the optimal state is reached.
[0055] 8. Calculate the geometric center position of the mark, or confirm the symmetry of the combined image with the cross.
[0056] Therefore, this embodiment can extract coordinates while focusing quickly, and in the semiconductor overlay process or testing process, it can quickly evaluate and confirm the imaging focal plane of the alignment system in a quantitative manner, thereby improving the accuracy and repeatability of the mark position calculation.
Claims
1. A photolithography alignment mark pattern structure supporting assisted focusing, having a first alignment mark main pattern of a cross shape and 4 second alignment mark main patterns of a square shape respectively nested in four quadrants of the cross shape, characterized in that: A first MTF target pattern is provided at each of the four ends of the cross shape of the first alignment mark main pattern, and a set of second MTF target patterns is provided at each of the four outer corners of the square shape of the second alignment mark main pattern.
2. The photolithographic alignment mark pattern structure supporting auxiliary focusing according to claim 1, characterized in that: The first MTF target pattern is a grid pattern, and the direction of the grid stripes is parallel to the width direction of the end of the cross-shaped pattern.
3. The photolithographic alignment mark pattern structure supporting auxiliary focusing according to claim 2, characterized in that: In the cross shape, the total length of the horizontal bars is equal to the total length of the vertical bars and they intersect at their respective midpoints to form a centrally symmetrical structure. The geometric centers of the first MTF target patterns at the four ends of the cross shape are located on the central symmetry axis of the cross shape. At the same time, the structure of each first MTF target is also centrally symmetrical about the central symmetry point of the cross shape.
4. The photolithographic alignment mark pattern structure supporting auxiliary focusing according to claim 1, characterized in that: The second MTF target pattern consists of a set of two mutually perpendicular grid patterns, with the two grid patterns located on the outer sides of the two sides forming the outer corners of the square.
5. The photolithographic alignment mark pattern structure supporting auxiliary focusing according to claim 4, characterized in that: The stripes of each grid are arranged perpendicular to the direction of the edge of the square they belong to.
6. The photolithographic alignment mark pattern structure supporting auxiliary focusing according to claim 1, characterized in that: The spatial resolution corresponding to a single pixel of the camera is denoted as d. All feature sizes of the first alignment mark main pattern, the second alignment mark main pattern, the first MTF target pattern, and the second MTF target pattern are integer multiples of d.
7. The photolithographic alignment mark pattern structure supporting auxiliary focusing according to claim 6, characterized in that: The MTF grid width does not exceed 4d.
8. The photolithographic alignment mark pattern structure supporting auxiliary focusing according to claim 7, characterized in that: The MTF grid width is d.