An alignment mark structure of SF155 photoetching machine

Abstract

The utility model belongs to the technical field of semiconductor wafer manufacturing, and relates to a kind of alignment mark structure of SF155 photoetching machine, for the photoetching alignment of Super Junction MOS double epitaxial process, including the X direction mark and Y direction mark being set on mask plate;The X direction mark and Y direction mark are all concave marks, and the concave mark is formed by etching on wafer surface;The width of X direction mark on mask plate is 20um, and interval is 40um;The Y direction mark is formed by the X direction mark clockwise rotation 90 °;The etching depth of concave mark on wafer is 1um.This application reduces the mark distortion after double epitaxial deposition by optimizing the shape, size and etching depth of mark, and improves the success rate of photoetching alignment.

Description

Technical Field

[0001] This utility model belongs to the field of semiconductor wafer manufacturing technology and relates to an alignment mark structure for an SF155 lithography machine. Background Technology

[0002] The SF155 lithography machine (NIKON stepper exposure equipment) is widely used in semiconductor wafer manufacturing. Its EGA alignment marking is divided into XY simultaneous measurement type and X and Y separate measurement type. In the manufacturing of planar MOS, MEMS, IGBT and other products, because the grown film is thin and there is no multilayer epitaxial deposition (EPIdep), the morphology distortion of the alignment mark is small and the distortion is low, so the alignment success rate is high.

[0003] However, in the Super Junction MOS manufacturing process, multilayer epitaxial deposition is required on the alignment marks, resulting in severe mark distortion. This causes the SF155 lithography machine to fail to recognize the marks, leading to alignment failure. Therefore, an optimized alignment mark structure is urgently needed to solve the mark recognition problem in multilayer epitaxial processes. Summary of the Invention

[0004] The purpose of this invention is to provide an alignment mark structure for an SF155 lithography machine, which solves the problem that the alignment mark in the existing Super Junction MOS double-layer epitaxial process (7.5um+7.5um) is distorted and cannot be identified due to the multi-layer epitaxial deposition.

[0005] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0006] An alignment mark structure for an SF155 lithography machine, used for lithographic alignment in Super Junction MOS bilayer epitaxial process, includes an X-direction mark and a Y-direction mark disposed on a mask; both the X-direction mark and the Y-direction mark are concave marks, which are formed by etching on the wafer surface;

[0007] The X-direction mark on the mask has a width of 20µm and a spacing of 40µm; the Y-direction mark is formed by rotating the X-direction mark 90° clockwise.

[0008] The depth of the concave mark on the wafer is 1µm.

[0009] Furthermore, the X-direction marking includes a central marking strip and side marking strips located on both sides of the central marking strip; the central marking strip is provided with one strip and its height on the wafer is 46 μm, and there are four side marking strips on each side, with the side marking strips having a height of 42 μm on the wafer.

[0010] Furthermore, the size ratio of the mask to the wafer is 4:1, and the actual width of the X-direction mark on the wafer is 5µm, with a spacing of 10µm.

[0011] The beneficial effects of this utility model are as follows:

[0012] This invention effectively solves the problem of distorted identification of alignment marks in multilayer epitaxial processes by optimizing the layout and size of mask markings, wafer etching depth and step height difference, and coordinating with lithography machine parameter adjustments. This enables the SF155 lithography machine to accurately identify marks in Super Junction MOS double-layer epitaxial processes, with an alignment accuracy of within ±0.1µm, significantly improving the success rate of lithography alignment. Attached Figure Description

[0013] Figure 1 Design drawing of alignment marks for the SF155 lithography machine on the photomask (marked separately in the X and Y directions);

[0014] Figure 2 This is a schematic diagram of the etching depth (etching depth 1µm) of the alignment mark on the wafer.

[0015] In the diagram, 1 is the center marker bar; 2 is the side marker bar. Detailed Implementation

[0016] The alignment mark structure of the SF155 lithography machine of this utility model will be described in detail below with reference to Figures 1-2 and specific parameters. This embodiment is applicable to the lithography alignment scenario of Super Junction MOS double-layer epitaxial process (7.5um+7.5um).

[0017] The mask marking structure design is shown in Figure 1. The alignment marking structure of this utility model includes X-direction markings and Y-direction markings, both of which are designed as concave markings (formed by etching away lines on the wafer to create the pattern).

[0018] X-direction marking group: Consists of 9 parallel grooves (grooved areas are light-transmitting areas), including one central marking strip 1 and four side marking strips 2 on each side. The width of the X-direction marking grooves on the mask is 20μm and the spacing is 40μm. Since the size ratio of the mask to the wafer is 4:1, the actual dimensions on the wafer are: a single groove width of 5μm and a spacing of 10μm between adjacent grooves. Among them, the length of the central groove on the wafer is 46μm, and the length of each of the four side grooves on the wafer is 42μm, forming a 4μm step height difference (46μm vs 42μm) to enhance the optical contrast after epitaxial coverage.

[0019] Y-direction marking group: formed by rotating the X-direction marking group 90° clockwise. Its size parameters (width, spacing, and length on the mask and wafer) are completely consistent with the X-direction marking group, except that the direction is perpendicular, ensuring that the lithography machine can independently identify the alignment information in the X and Y directions.

[0020] As shown in Figure 2, the etching depth of the marker on the silicon wafer surface is 1µm. This depth design can effectively reduce the marker distortion after the double-layer 7.5µm epitaxial deposition.

[0021] In practical applications, after marking and etching are completed, two 7.5µm epitaxial layers are grown on the wafer. Although the markings are somewhat distorted at this time, the markings can be clearly identified by adjusting the alignment parameters of the lithography machine's exposure formula (such as setting the marking width to 6µm, the recognition frame to 16, and the focus compensation value to 6µm). This ultimately achieves precise lithographic alignment of the Super Junction MOS double-layer epitaxial process, with alignment accuracy meeting the requirement of within ±0.1µm.

[0022] The wafer groove markings are fabricated by etching an array of grooves on the surface of a silicon substrate that correspond to the mask markings. The specific characteristics are as follows:

[0023] Etching depth: Strictly controlled at 1.0 μm, with an allowable deviation of ±0.05 μm. This depth design effectively disperses stress during the epitaxial growth process, preventing cracking at the marking edges due to stress concentration, while preserving a recognizable contour base after the epitaxial layer is covered.

[0024] Groove dimensions: After etching, the bottom width of the groove on the wafer is 5μm, and the spacing between adjacent grooves is 10μm, matching the size ratio (4:1) of the mask; the roughness of the etched surface must meet the optical recognition requirements of the SF155 lithography machine (surface undulation ≤0.1μm) to ensure the clarity of the initial marking.

[0025] X / Y Marker Separation: The physical spacing between the X-direction marker group and the Y-direction marker group on the wafer is ≥100μm, which avoids bidirectional distortion superposition interference and improves the independent calibration accuracy of the lithography machine in the X and Y directions.

[0026] After completing the wafer groove marking etching, two 7.5μm epitaxial layers (total thickness 15μm) are grown sequentially. At this time, the marking structure undergoes the following changes:

[0027] The groove is partially filled by the epitaxial layer, and the depth is reduced compared to the initial etching depth. However, due to the design of the initial etching depth (1.0 μm), the identifiable concave contour is still retained.

[0028] The marker edges form a gentle slope morphology due to the lateral growth of the epitaxial layer (i.e., "distortion phenomenon"). However, the central groove (46 μm long) still maintains a relatively prominent outline after the gentle slope is formed because there is a 4 μm step height difference between it and the two side grooves (42 μm long). The optical contrast is better than that of the marker without step design.

[0029] To accommodate the distortion of the markers after epitaxy, the exposure recipe parameters of the SF155 lithography machine were adjusted as follows:

[0030] Marker width setting: The mark width recognized by the lithography machine is adjusted to 6μm to compensate for the expansion of the groove linewidth caused by the epitaxial layer coverage;

[0031] Frame size: set to 16 to ensure coverage of the 46μm long central marker area and reduce interference from edge distortion on recognition;

[0032] Focus compensation value: adjusted to +6μm to offset the focal plane shift caused by the epitaxial layer thickness and ensure clear marking imaging.

[0033] Through the above structural design and parameter adaptation, the success rate of distortion mark recognition and photolithography alignment accuracy are improved in the photolithography operation of Super Junction MOS double-layer epitaxial process (7.5um+7.5um), meeting the manufacturing accuracy requirements of super junction MOS devices.

[0034] It should be understood that the embodiments described above are merely illustrative of the present invention and are not intended to limit the present invention. All other embodiments obtained by those skilled in the art based on the above embodiments without creative effort are within the scope of protection of the present invention.

Claims

1. An alignment mark structure for an SF155 lithography machine, characterized in that, Photolithographic alignment for Super Junction MOS bilayer epitaxial process includes X-direction marks and Y-direction marks disposed on a mask; both the X-direction marks and the Y-direction marks are concave marks, which are formed by etching on the wafer surface; The X-direction markings on the mask have a width of 20µm and a spacing of 40µm. The Y-direction mark is formed by rotating the X-direction mark 90° clockwise; The depth of the concave mark on the wafer is 1µm.

2. The alignment mark structure of the SF155 lithography machine according to claim 1, characterized in that, The X-direction marking includes a central marking strip (1) and side marking strips (2) located on both sides of the central marking strip (1); the central marking strip (1) has one strip with a height of 46 μm on the wafer, and four side marking strips (2) are provided on each side, with a height of 42 μm on the wafer.

3. The alignment mark structure of the SF155 lithography machine according to claim 1, characterized in that, The size ratio of the mask to the wafer is 4:1, and the actual width of the X-direction mark on the wafer is 5µm, with a spacing of 10µm.

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