CN116449643A

CN116449643A - High-precision ultraviolet lithography alignment mark and alignment method

Info

Publication number: CN116449643A
Application number: CN202310230696.6A
Authority: CN
Inventors: 沈超; 王军飞; 易淑兰; 栗东
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2023-03-11
Filing date: 2023-03-11
Publication date: 2023-07-18

Abstract

The invention belongs to the technical field of wireless optical communication, and particularly relates to an ultraviolet lithography overlay registration mark and an overlay method. The ultraviolet lithography overlay register mark comprises three parts: the hollow square frame in the middle of the register mark and the cross part in the middle of the square frame are used for rough alignment; the digital parts of the register mark, which correspond to the four vertexes of the hollow square frame, are used for marking the serial numbers of the sub-register which need to be subjected to alignment; 4 graduated scales which are positioned at the upper, lower, left and right sides and correspond to the outer sides of the four sides of the hollow square frame in the register mark are used for fine alignment; the master plate is provided with 4 graduated scales as main graduations, and the sub-plate is provided with 4 graduated scales as sub-graduations. The invention greatly improves the alignment precision of ultraviolet lithography while simultaneously improving the definition of the ultraviolet lithography pattern and facilitating the movement alignment. The register mark can simultaneously meet the overlay requirements of the bright plate and the dark plate. The overlay method has no limit on the layer number of the layout, and the overlay patterns of the subsequent layout are completely drawn in the first step process, so that the defect of overlay error superposition is avoided.

Description

High-precision ultraviolet lithography alignment mark and alignment method

Technical Field

The invention belongs to the technical field of wireless optical communication, and particularly relates to an alignment mark for ultraviolet lithography and an alignment method.

Background

Ultraviolet lithography is an important part of microelectronic and optoelectronic chip processing. For photolithography, alignment is the most important step. The process is tightly combined with the subsequent operations such as etching coating and the like in a processing area, and the accuracy of chip processing is determined. In order to fully develop the precision of the ultraviolet lithography machine, proper register marks are particularly important. First, the register marks need to be of a suitable size because the microscope of the uv lithography machine has a fixed magnification. The register mark is too large to be convenient for the lens to see the register mark and align the whole picture. The register mark is too small to be clearly resolved, and accurate register cannot be performed. Secondly, since the reticle is divided into a shadow region and a non-shadow region. The shadow area is too large to facilitate viewing alignment. In addition, if all register marks are aligned exactly, there is a corresponding difficulty in distinguishing whether the alignment itself is aligned, especially for alignment on the sub-micron scale.

Most of the existing purple photoetching register marks are directly designed with alignment patterns, such as patterns which are identical or consistent with each other by using a master plate and a sub plate, and the register marks are difficult to achieve accurate alignment. The difficulty is as follows: firstly, the register mark needs to be proper in size, can be completely displayed under a microscope of an ultraviolet photoetching machine and can be clearly observed; second, it is difficult to precisely align the fine pattern. Because the processing processes such as etching, coating and the like cannot completely transfer the pattern to the epitaxial wafer without damage due to the deviation of the processing process, the layout pattern on the surface of the epitaxial wafer has corresponding defects; in addition, the photolithography version has a certain thickness, and accurate focusing is difficult to realize. Therefore, the alignment mode of simply judging whether the sub-plate and the master plate are overlapped cannot realize higher photoetching precision.

Therefore, it is desirable to design register marks that enable both convenient coarse alignment and quick accurate alignment. Since the uv lithography microscope magnification is typically fixed, for example, 10X is common. In order to find the register mark conveniently, the method for realizing the quick coarse alignment is particularly important to plan the size of the microscope coarse register mark and the size of the microscope fine register mark. In order to reduce the difficulty of precise alignment and to exert the highest alignment potential of the ultraviolet lithography machine, improvement of the precise alignment mark is required.

Disclosure of Invention

The invention aims to provide an ultraviolet lithography alignment mark and an alignment method which can be used for conveniently and coarsely aligning and rapidly and accurately aligning.

The invention provides an ultraviolet lithography overlay registration mark, which comprises a master plate and a sub-plate; the device comprises 3 main body parts:

a main body part 1, which is a hollow square frame in the middle of the register mark and a cross part in the middle of the square frame, and is used for rough alignment; see fig. 1;

the main body part 2 is a digital part corresponding to four vertexes of the hollow square frame in the register mark and is used for marking a sub-register serial number which needs to be subjected to alignment; see fig. 4;

the main body part 3 is provided with 4 graduated scales which are positioned at the upper, lower, left and right sides and correspond to the outer sides of the four sides of the hollow square frame in the register mark and used for fine alignment; the 4 graduated scales corresponding to the master plate are called main graduations, the 4 graduated scales corresponding to the sub-plates are called sub-graduations and are used for fine alignment; see fig. 5.

Each part of the register mark has a corresponding function, so that an operator can conveniently and rapidly align the register mark by using the register mark, meanwhile, the precision alignment difficulty is greatly reduced, the reading deviation is amplified, and the alignment precision is effectively improved; in the actual alignment process, because symmetrical deviation should appear on the left and right sides after alignment, repeated confirmation of whether the scale bars are aligned is not needed; and the further from the center, the larger the offset is, so that an operator can more easily observe the offset direction and the offset size of the sub-plate relative to the master plate.

In the main body portion 1:

in the mother plate, the inner side size of the rectangular square frame is as follows: the length (long side) is 50 μm-500 μm, and the width (short side) is 10 μm-500 μm; a middle cross part, the length of the line is 180-220 mu m, and the width of the line is 40-60 mu m; preferably: the inner side length of the hollow square frame part is 260 mu m; a middle cross portion having a line length of 200 μm and a line width of 50 μm;

in the sub-version, the long side and the short side of the rectangular box are slightly smaller than the size of the master, and the rectangular box can be reserved or not; the line length and line width of the middle cross part are slightly smaller than the line length and width of the cross part in the master plate respectively, and are usually designed to be 10 mu m smaller, so that even if the pattern edge on the mask plate is damaged, the alignment of the sub-plate in the middle of the master plate can be ensured.

When the sub-plate is roughly aligned with the master plate under the microscope of the photoetching machine, the morphology after the cross is overlapped is shown in figure 3, and the cross (gray) on the sub-plate is in the middle of the cross (purple) of the master plate.

In the main body part 2, the numbers on the mother set are used for marking the serial numbers of the sub-sets for subsequent overlay. For example, in fig. 4, the red box is marked with 1, i.e., the overlay is to be performed with sub-plate 1. The digital portion is not necessary for the sub-version, but is merely an register mark that is used to indicate which serial number to select for each overlay.

In the main body part 3, the master plate comprises 4 graduated scales at the upper, lower, left and right, and each graduated scale consists of a main graduation and a sub graduation. Wherein:

the length of the scale mark in the main scale is 20-100 mu m, and the width is 1-20 mu m; preferably, the main score line has a length of 40 μm and a width of 5 μm; the gap between two adjacent graduations is 5-20 μm, preferably 10.1 μm;

the length of the graduation mark in the sub-graduation is 10-100 μm, the width is 1-20 μm, the length of the sub-graduation mark is 20 μm, and the width is 5 μm; the gap between two adjacent graduation marks of the sub-graduation is slightly smaller than the gap between two adjacent graduation marks in the main graduation, for example, when the gap of the main graduation is 10.1 mu m, the gap of the sub-graduation is 10 mu m, and the deviation of 0.1 mu m exists;

in the scale, the main scale is usually provided with an odd number of scale marks, the sub-scale is usually provided with an even number, and the number of the sub-scale marks is not limited too much.

The main scale uses the middle scale line as the alignment base line, the left and right (up and down) of the main scale line are sequentially provided with a plurality of (for example, 10) scale lines for calculating the deviation, and the number of the scale lines is not limited and is usually an integer multiple of 5.

In each scale, the sub-scale is located in the middle of the main scale, see fig. 7, the sub-scale is a middle light line portion, and the main scale is a dark color portion.

During ultraviolet lithography, the photolithography mask is used for transferring the photolithography pattern onto the epitaxial wafer. In the following description, the first block of reticle is referred to as the master, numbered 0. The subsequent photoetching plate which needs to be subjected to alignment according to the epitaxial wafer pattern is called a sub-plate, and the marks are respectively 1,2 and 3 … …; the master plate does not need to be subjected to overlay, the graph on the photoetching plate is copied to the epitaxial wafer, and the graph also comprises the alignment mark of the sub-plate required by subsequent overlay. Each sub-plate is provided with a dedicated plate alignment mark on the epitaxial wafer. For example: when the sub-plate 1 is in alignment, an alignment mark with the serial number 1 needs to be found on the epitaxial wafer for alignment.

The ultraviolet lithography machine generally selects a fixed 10x microscope lens, and the display screen is fixed in size. Therefore, the size of the photomask register mark is reasonably set. If the register mark pattern is too large, only part of the pattern can be displayed on the display screen, and the microscope lens needs to be repeatedly moved while the alignment is performed, so that the alignment conditions of different positions of the epitaxial wafer can be observed, and the alignment difficulty of the alignment is greatly increased. On the contrary, if the register mark pattern is too small, although the whole register mark can be observed in the same field of view, it is difficult for the naked eye to distinguish the relative positions of the epitaxial wafer and the photomask, and thus high-precision alignment cannot be realized.

The invention takes a SUSS-MA6 photoetching machine which is most commonly used in ultraviolet photoetching as an example, and introduces the specific application of the register mark in the photoetching process. The photoetching process is to uniformly coat a layer of photoresist on the surface of an epitaxial wafer, and then transfer a mask pattern onto the photoresist by using an ultraviolet photoetching machine. Photoresists have very strong photosensitive characteristics, i.e., the characteristics vary significantly for exposed and non-exposed areas. By utilizing the characteristic, different areas of the epitaxial wafer are selectively exposed, so that the pattern of the photoetching mask plate is transferred to the photoresist of the epitaxial wafer. It should be noted that the exposure process covers the entire epitaxial wafer, but selective exposure can be achieved because the photolithographic reticle has a light transmissive portion and a light opaque portion.

After the first exposure and subsequent development, etching, etc., processes are completed, the desired pattern will be formed on the epitaxial wafer. Micro-nano machining is a high-precision machining on the scale of micrometers or even nanometers, so that the subsequent process needs to precisely machine a specific area. In addition to the first photolithography process, the following photolithography process focuses on alignment processing, i.e., overlay.

The invention provides a high-precision ultraviolet lithography register mark, which is specifically applied to lithography and comprises the following steps:

step one: and cleaning the epitaxial wafer, and spin-coating photoresist on the clean surface of the epitaxial wafer. Selecting specific positive photoresist or negative photoresist according to the pattern of the photoetching pattern;

step two: a first photolithography is performed. Transferring the master pattern onto the epitaxial wafer photoresist. The process does not need alignment operation, and only needs to ensure that the distribution of the photoetching patterns on the epitaxial wafer is as symmetrical as possible;

step three: and carrying out secondary photoetching after carrying out subsequent operations such as development, film hardening, etching and the like on the epitaxial wafer. The process is overlay, and the sub-plate register mark is aligned with the register mark of the corresponding serial number of the master plate during photoetching; firstly, matching rectangular boxes of the main body part 1 and roughly aligning cross parts; then, the fine alignment of the graduated scale of the main body part 1 is carried out, and the calibration basis is that the graduation lines at the centers of the master plate and the sub-plate are aligned left and right, and the graduation lines at the left and right have accumulated deviation;

step four: and carrying out a subsequent alignment process according to the micro-nano processing requirement, wherein the specific operation is consistent with the third step.

The ultraviolet lithography overlay registration mark designed by the invention is a consistent brand new registration mark, and can greatly improve the overlay precision of ultraviolet lithography while improving the definition of ultraviolet lithography patterns and facilitating the movement alignment. The register mark can simultaneously meet the overlay requirements of the bright plate and the dark plate. For different patterns required by the light plate and the dark plate, operators can realize ultra-high precision overlay by only carrying out the same plate alignment operation. The overlay process is not particularly limited on the layer number of the layout, and the overlay patterns of the subsequent layout can be completely drawn in the first step process, so that the defect of overlay error superposition is avoided.

Drawings

Fig. 1 is a schematic view of a main body portion 1 of a master registration mark of the present invention.

FIG. 2 is a schematic illustration of register marks on a plain version of the present invention.

Fig. 3 is a schematic diagram of the superposition morphology of the registration mark main body part 1 under the microscope of the invention.

Fig. 4 is a schematic view of a main body portion 2 of a master registration mark of the present invention.

Fig. 5 is a schematic view of a main body portion 3 of a master registration mark of the present invention.

Fig. 6 is a schematic of a graduated scale on a subversion of the invention.

FIG. 7 is a schematic diagram of the topology of the present invention in which the sub-layout coincides with the master layout.

FIG. 8 is an enlarged schematic view of the scale of the present invention.

FIG. 9 is a schematic representation of the topography of a subplate of the present invention shifted to the left by 0.1 μm.

FIG. 10 is a schematic representation of the morphology of a subplate of the present invention shifted to the right by 0.1 μm.

Detailed Description

The invention is further illustrated by the following examples in connection with the accompanying drawings.

In the main body portion 1:

in the mother plate, the inner side length of the hollow square frame part is 260 mu m; a middle cross portion having a line length of 200 μm and a line width of 50 μm;

in the sub-plate, the long side and the short side of the rectangular square frame are slightly smaller than the size of the master plate, and the line length and the line width of the middle cross part are respectively smaller than the line length and the wide line width of the cross part in the master plate by 10 mu m, so that even if the edge of a pattern on the mask plate is damaged, the sub-plate can be ensured to be in the middle of the master plate during alignment.

in the main scale, the length of the scale mark is 40 μm, and the width is 5 μm; the gap between two adjacent scales is 10.1 mu m;

in the sub-scale, the length of the scale mark is 20 μm, and the width is 5 μm; the gap between two adjacent graduation marks is 10 μm, representing a deviation of 1 μm.

The main scale uses the middle scale line as the alignment baseline, and the left and right (up and down) of the main scale line are sequentially provided with a plurality of (e.g. 10) scale lines for calculating the deviation.

Shown in the red line box in fig. 1 is the subject portion 1 of the master registration mark, with the middle cross portion and the open box portion for coarse alignment.

The morphology of the sub-plate overlapped with the rough alignment cross of the master plate under the microscope of the photoetching machine is shown in figure 3, and the gray cross on the sub-plate is arranged in the middle of the purple cross of the master plate.

The main body part 2 on the master is a number in a red frame for marking a sub-version number for subsequent overlay. For example, in fig. 4, the red box is marked with 1, i.e., the overlay is to be performed with sub-plate 1. The digital portion is not necessary for the sub-version, but is merely an register mark that is used to indicate which serial number to select for each overlay.

When the main body part 3 is precisely aligned, the shape of the sub-layout overlapped with the master pattern is shown in fig. 7. The sub-layout is a gray layout, the coarse alignment mark cross is positioned in the middle of the master pattern cross, and the scale of the sub-layout is positioned in the middle of the scale of the master pattern. When the two are fully aligned, the magnified topography shown on the microscope of the lithography machine is shown in FIG. 8. The most intermediate primary graduations are aligned. The graduation lines on the sub-layout are offset towards the center relative to the master layout. For convenience of description, scales are numbered. When the master is perfectly aligned with the sub-plates, the sub-plates at the-1 scale are offset 0.1 μm to the right with respect to the master, the sub-plates at 1 are offset 0.1 μm to the left with respect to the master, the sub-plates at-2 are offset 0.2 μm to the right with respect to the master, and the sub-plates at 2 are offset 0.2 μm to the left with respect to the master. The sub-plate at 3 is offset 0.3 μm to the right with respect to the master and the sub-plate at 3 is offset 0.3 μm to the left with respect to the master. And so on, the offset of each subsequent sub-engraving relative to the master scale will be superimposed accordingly.

When the subplate is offset to the left by 0.1 μm, the scale bars at-1 are aligned. The sub-engraving bars at 0 are offset to the left by 0.1 μm relative to the master scale bars, and the sub-engraving bars at-2 are offset to the right by 0.1 μm relative to the master scale bars. The sub-engraving scale bar at 1 is offset to the left by 0.2 μm relative to the master scale bar, and the sub-engraving scale bar at-3 is offset to the right by 0.2 μm relative to the master scale bar. And so on.

When the sub-plate is shifted 0.1 μm to the right, the scale bars at the 1 scale are aligned. The sub-engraving scale bars at the 0 scale are offset to the right by 0.1 μm relative to the master, and the sub-engraving scale bars at-1 are offset to the right by 0.2 μm relative to the master. The sub-engraving bars at-2 are offset 0.3 μm to the right with respect to the master. And so on. The sub-plate scale bars at 2 are offset to the left by 0.1 μm with respect to the master scale bars, and the sub-plate scale bars at 3 are offset to the left by 0.2 μm with respect to the master.

From the above, it can be derived that when the 0 scale bar is aligned, the master is perfectly aligned with the sub-plate. At this time, the scale bar on the left side of the sub-plate 0 is shifted to the right relative to the scale bar of the master, and the scale bar on the right side of the sub-plate 0 is shifted to the left relative to the master. The farther the scale bar is from 0, the more the scale bar is offset. When the master sub-plate scale bar at-1 is aligned, the sub-plate is offset to the left relative to the master by 0.1 μm, and when the sub-plate scale bar at-2 is aligned relative to the master, the sub-plate is offset to the left by 0.2 μm relative to the master. And so on. When the scale bar at sub-plate 1 is aligned with respect to the master, the sub-plate is offset to the right by 0.1 μm with respect to the master, and when the scale bar at sub-plate 2 is aligned with respect to the master, the sub-plate is offset to the right by 0.2 μm with respect to the master. And so on.

Conventional register marks are judged only by whether all the graduation marks are aligned, but small deviations are extremely difficult for human eyes to distinguish. The register mark used by the invention can observe symmetrical offset respectively appearing on the left side and the right side after alignment besides taking the central scale mark as a reference. The larger the offset toward the edge, the larger the offset is, which is equivalent to amplifying the offset, and thus the human eye calibration is facilitated.

The longitudinal scale is the same as the transverse principle. For the negative plate, only the graph area and the non-graph area in the area are exchanged, and the display effect under the microscope of the photoetching machine is not different from that of the positive plate.

The division of the steps in this embodiment is only for clarity of description, and it is possible to combine the steps into one step or split some steps into multiple steps in implementation, so long as the same logic relationship is included, which is within the protection scope of this patent.

It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples of carrying out the invention and that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. A high-precision ultraviolet lithography overlay registration mark, wherein the registration mark comprises a master plate and a sub-plate; the utility model is characterized in that the utility model is divided into 3 main body parts:

a main body part 1, which is a hollow square frame in the middle of the register mark and a cross part in the middle of the square frame, and is used for rough alignment;

the main body part 2 is a digital part corresponding to four vertexes of the hollow square frame in the register mark and is used for marking a sub-register serial number which needs to be subjected to alignment;

the main body part 3 is provided with 4 graduated scales which are positioned at the upper, lower, left and right sides and correspond to the outer sides of the four sides of the hollow square frame in the register mark and used for fine alignment; the master plate is provided with a master plate, wherein 4 graduated scales of the master plate are called main graduations, and 4 graduated scales of a sub plate are called sub graduations.

2. The high-precision uv lithography overlay mark according to claim 1, wherein the body portion 1:

in the mother plate, the inner side size of the rectangular square frame is as follows: the length is 50 μm-500 μm, and the width is 10 μm-500 μm; a middle cross part, the length of the line is 180-220 mu m, and the width of the line is 40-60 mu m;

in the sub-plate, the long side and the short side of the rectangular square frame are slightly smaller than the size of the master plate, and the rectangular square frame is reserved or not reserved; the line length and the line width of the middle cross part are slightly smaller than the line length and the wide line width of the cross part in the master plate respectively; when the sub-plate is roughly aligned with the master plate under the microscope of the photoetching machine, the cross on the sub-plate is arranged in the middle of the cross of the master plate.

3. The high-precision uv lithography overlay mark according to claim 2, wherein the main body portion 3:

the length of the scale mark in the main scale is 20-100 mu m, and the width is 1-20 mu m; the gap between two adjacent scales is 5-20 mu m;

the gap between two adjacent graduation marks of the sub graduation is slightly smaller than the gap between two adjacent graduation marks in the main graduation, which represents deviation;

in the graduated scale, the main graduation has odd graduation marks, and the sub graduation has even graduation marks;

the main scale takes the middle scale line as an alignment baseline, and a plurality of scale lines are sequentially arranged at the left and right or the upper and lower parts of the main scale line and are used for calculating deviation;

when aligning, in each graduated scale, the sub-graduation is positioned at the middle position of the main graduation.

4. The high-precision uv lithography overlay mark as claimed in claim 3, wherein the body portion 1: in the mother plate, the inner side length of the hollow square frame part is 260 mu m; a middle cross portion having a line length of 200 μm and a line width of 50 μm;

in the sub-plate, the line length and line width of the middle cross portion are 10 μm smaller than the line length and width of the cross portion in the master, respectively.

5. The high-precision uv lithography overlay mark according to claim 4, wherein the body portion 3:

the length of the scale mark in the main scale is 40 mu m, and the width is 5 mu m; the gap between two adjacent scales is 10.1 mu m;

the length of the scale mark in the sub scale is 20 mu m, and the width is 5 mu m; the gap between two adjacent graduation marks is 10 μm, and the deviation of 1 μm exists.

6. The high-precision uv lithography overlay mark of claim 5, wherein the sub-plate coincides with the master when fine alignment is performed; the rough alignment mark sub-plate cross is positioned in the middle of the master plate cross; the graduated scale of the neutron plate of the fine alignment mark is positioned in the middle of the graduated scale of the master plate; when the two are completely aligned, the most middle main inscription line is aligned; the scale lines on the sub-plate are offset towards the center relative to the master plate; for convenience of description, scales are numbered; when the master is fully aligned with the sub-plates, the sub-plates at the-1 scale are offset 0.1 μm to the right relative to the master, the sub-plates at 1 are offset 0.1 μm to the left relative to the master, the sub-plates at-2 are offset 0.2 μm to the right relative to the master, and the sub-plates at 2 are offset 0.2 μm to the left relative to the master; -the sub-plate at 3 is offset 0.3 μm to the right with respect to the master and the sub-plate at 3 is offset 0.3 μm to the left with respect to the master; by analogy, the offset of each subsequent sub-engraving scale relative to the master scale is correspondingly overlapped;

when the subplate is offset to the left by 0.1 μm, the scale bars at-1 are aligned; the sub-engraving scale bar at 0 is offset to the left by 0.1 mu m relative to the master scale bar, and the sub-engraving scale bar at-2 is offset to the right by 0.1 mu m relative to the master scale bar; the sub-engraving scale bar at 1 is offset by 0.2 mu m leftwards relative to the master scale bar, and the sub-engraving scale bar at-3 is offset by 0.2 mu m rightwards relative to the master scale bar; and so on;

when the sub-plate is shifted to the right by 0.1 μm, the scale bars at the 1 scale are aligned; the sub-engraving scale bars at the 0 scale are shifted to the right by 0.1 mu m relative to the master, and the sub-engraving scale bars at the-1 scale are shifted to the right by 0.2 mu m relative to the master; the sub-engraving bars at-2 are offset 0.3 μm to the right with respect to the master; and so on; the sub-plate scale bar at 2 is offset to the left by 0.1 μm relative to the master scale bar, and the sub-plate scale bar at 3 is offset to the left by 0.2 μm relative to the master;

according to the different conditions, when the 0 scale bar is aligned, the master plate and the sub-plate are completely aligned; at this time, the scale bar at the left side of the sub-plate 0 is offset to the right relative to the scale bar of the master, and the scale bar at the right side of the sub-plate 0 is offset to the left relative to the master; the farther the scale bar is from 0, the more the scale bar is offset; when the scale bar of the master plate at the position-1 is aligned, the sub plate is offset to the left by 0.1 mu m relative to the master plate, and when the scale bar of the master plate at the position-2 is aligned relative to the master plate, the sub plate is offset to the left by 0.2 mu m relative to the master plate; and so on; when the scale bar at sub-plate 1 is aligned relative to the master, the sub-plate is offset to the right by 0.1 μm relative to the master, and when the scale bar at sub-plate 2 is aligned relative to the master, the sub-plate is offset to the right by 0.2 μm relative to the master; and so on.

7. Method for overlay of plate marks based on high precision uv lithography overlay according to one of claims 1-6, characterized by the steps of:

step one: cleaning the epitaxial wafer, and spin-coating photoresist on the surface of the clean epitaxial wafer; selecting specific positive photoresist or negative photoresist according to the pattern of the photoetching pattern;

step two: performing first photoetching, and transferring a master pattern onto the epitaxial wafer photoresist; the alignment operation is not performed, so that the distribution symmetry of the photoetching plate patterns on the epitaxial wafer is ensured;

step three: performing secondary photoetching after subsequent operations of developing, hardening and etching on the epitaxial wafer; namely, overlay is carried out, and the sub-version register marks are aligned with the register marks of corresponding serial numbers of the master plate during photoetching; firstly, matching rectangular boxes of the main body part 1 and roughly aligning cross parts; then, the fine alignment of the graduated scale of the main body part 1 is carried out, and the calibration basis is that the graduation lines at the centers of the master plate and the sub-plate are aligned left and right, and the graduation lines at the left and right have accumulated deviation;