Preparation method of novel composite substrate ultrathin functional layer structure

Abstract

The invention relates to a preparation method of a novel composite substrate ultrathin functional layer structure, and relates to the technical field of semiconductors, and the preparation method comprises the following steps: S1, growing a buffer layer and an ultrathin functional layer on a first substrate; s2, patterning the ultrathin functional layer to form an independent functional layer thin film; s3, coating photoresist in the groove to form a temporary support layer; s4, removing the first part; s5, activating the surfaces of the functional layer films on the second substrate and the first substrate; s6, bonding the second substrate with the functional layer film on the first substrate; s7, removing the first substrate; s8, carrying out CMP wet polishing to remove the buffer layer; and S9, the second part is removed. According to the invention, shape mutation generated by the functional layer thin film is reduced, stress concentration generated by the edge of the functional layer thin film is reduced, the edge of the functional layer thin film can be effectively prevented from being broken during polishing, and the yield of the ultrathin functional layer structure of the composite substrate is improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a method for preparing a novel composite substrate ultra-thin functional layer structure. Background Art

[0002] Heterogeneous integration can achieve the coordinated optimization of multiple functions by integrating materials with different functions on the same platform. It plays an important role in improving system performance, meeting complex application requirements and breaking through material performance bottlenecks. It has shown broad application prospects in the fields of high-performance computing, photonic chips, flexible devices, autonomous driving and post-Moore era technology development.

[0003] The invention publication number CN118824846A discloses a composite substrate ultra-thin functional layer structure and a preparation method thereof. In step 7 of Example 1, 200nm of AlN is completely removed by CMP wet polishing and thinning to obtain a composite substrate structure consisting of a 6-inch SiC-based wafer and a GaN HEMT functional layer with a thickness of 2μm bonded and transferred to the surface of the SiC wafer. In the related prior art, when the buffer layer (AlN) needs to be completely removed, the GaN HEMT functional layer is polished. Since the GaN HEMT functional layer is divided into an island structure, the edge of the ultra-thin functional layer is prone to stress concentration and breakage during polishing and thinning, resulting in a decrease in the yield of the composite substrate ultra-thin functional layer structure. Summary of the invention

[0004] In order to improve the problem that stress concentration and breakage easily occur at the edge of the ultra-thin functional layer during polishing and thinning, resulting in a decrease in the yield of the ultra-thin functional layer structure of the composite substrate, the present application provides a novel method for preparing the ultra-thin functional layer structure of the composite substrate.

[0005] The present application provides a novel method for preparing an ultra-thin functional layer structure of a composite substrate using the following technical solution: A method for preparing a novel composite substrate ultra-thin functional layer structure comprises the following steps: S1, sequentially epitaxially growing a buffer layer and an ultra-thin functional layer structure lattice-matched with the first substrate on the first substrate; S2, patterning the ultra-thin functional layer on the first substrate, wherein the ultra-thin functional layer is divided into mutually independent functional layer films located on the surface of the first substrate; S3, coating a photoresist in a groove between the functional layer films, and allowing the photoresist to solidify into a temporary support layer; S4, removing a first portion of the temporary support layer on the functional layer film to reduce the thickness of the temporary support layer, wherein a second portion of the temporary support layer is located in the groove between the functional layer films and does not Covering the upper surface of the functional layer film; S5, performing activation treatment and cleaning process, respectively treating the bonding surface of the target second substrate and the upper surface of the functional layer film on the first substrate; S6, bonding the bonding surface of the target second substrate and the upper surface of the first substrate to form the functional layer film; S7, removing the first substrate to expose the buffer layer; S8, removing the buffer layer to expose the lower surface of the functional layer film, the buffer layer is removed by CMP wet polishing; S9, removing the temporary supporting layer to expose the grooves between the functional layers, wherein the functional layer film is combined on the second substrate, and the grooves reveal the side walls of the functional layer film.

[0006] By adopting the above technical solution, by removing the first part, it is possible to avoid the first part hindering the bonding between the second substrate and the functional layer film, thereby ensuring the bonding effect between the second substrate and the functional layer film. After the buffer layer is completely removed, when the buffer layer is removed by CMP wet polishing, the functional layer film is polished and ground. Since the second part is filled in the groove, the shape mutation of the functional layer film is reduced, and the stress concentration generated at the edge of the functional layer film is reduced, which can effectively avoid the occurrence of the phenomenon of the edge of the functional layer film being broken during polishing, thereby improving the yield rate of the ultra-thin functional layer structure of the composite substrate.

[0007] Preferably, in step S3, the photoresist is coated in the groove by spin coating. First, a small amount of photoresist is dropped on the center of the ultra-thin functional layer, and then the first substrate is rotated. The photoresist spreads to the groove and the functional layer film under the action of centrifugal force, and then is baked to form a temporary supporting layer located on the buffer layer.

[0008] By adopting the above technical solution, the photoresist is spin-coated in the groove by spin coating, and a temporary support layer is formed on the buffer layer after baking, so that the temporary support layer has high uniformity and strong controllable thickness.

[0009] Preferably, in step S4, the first portion is removed by polishing and grinding, and the polishing and grinding starts from the upper surface of the first portion and stops at the upper surface of the functional layer film, so that the surface of the second portion is flush with the surface of the functional layer film.

[0010] By adopting the above technical solution, the first part is ground and removed by polishing, so that the surface of the temporary support layer is coplanar with the surface of the functional layer film, thereby effectively avoiding the influence of the first part on the bonding between the functional layer film and the second substrate, thereby ensuring the bonding effect between the functional layer film and the second substrate.

[0011] Preferably, in step S4, the first portion is removed by a stripping process, and the second portion is thinned by a stripping process, so that the upper surface of the second portion is closer to the buffer layer than the upper surface of the functional layer film.

[0012] By adopting the above technical solution, when the functional layer film is bonded to the second substrate, the temperature needs to be increased during the bonding process. The second part will expand as the temperature rises. The expansion will cause the surface of the second part to exceed the surface of the functional layer film, thereby affecting the bonding between the ultra-thin functional layer and the second substrate. To this end, the first part is completely removed and the second part is partially removed by adopting a stripping process, so that the thickness of the second part is less than the depth of the groove. When the second part expands due to heating, the second part will not exceed the groove, effectively avoiding the influence of the thermal expansion of the second part on the bonding of the functional layer film, thereby improving the bonding effect between the functional layer film and the second substrate.

[0013] Preferably, the stripping process includes: adjusting the upper surface of the first part to be parallel to the liquid surface of the dissolving solution, moving the first substrate downward, immersing the first part in the dissolving solution, and partially immersing the second part in the dissolving solution, so that the first part is completely removed and the second part is partially removed.

[0014] By adopting the above technical scheme, the target object is dissolved and removed by the dissolving liquid, the convenience of removing the first part is improved, the downward movement of the first substrate is controlled, the depth of the second part immersed in the dissolving liquid is controlled, and then the removal amount of the second part is controlled, thereby improving the accuracy and convenience of controlling the removal amount of the second part.

[0015] Preferably, in the stripping process, the process of immersing the first part and the second part in the dissolving solution is observed by a microscope magnification system, and the operator adjusts the immersion amount of the first part and the second part through the display of the microscope magnification system.

[0016] By adopting the above technical solution, the depth of the temporary support layer immersed in the dissolving liquid is observed using a microscope magnification system, which facilitates timely control of the depth of the temporary support layer immersed in the dissolving liquid and accurate control of the thickness of the temporary support layer in the groove.

[0017] Preferably, in step S8, CMP wet polishing includes: first selecting a polishing liquid that can chemically react with the surface of the buffer layer, the chemical reaction can convert the insoluble matter of the buffer layer into a soluble matter or soften the high-hardness substance, and then using a polishing head to press the buffer layer onto the polishing pad and drive the buffer layer to rotate, so that the abrasive particles in the grinding liquid produce mechanical friction with the buffer layer, thereby removing the buffer layer.

[0018] By adopting the above technical solution, the dissolution and softening effect between the polishing liquid and the buffer layer can be used to improve the global flattening ability of the buffer layer surface, and achieve high precision and high flatness of the buffer layer grinding. At the same time, the difference in removal rate between hard materials and soft materials is minimized to the greatest extent, avoiding surface damage caused by simple mechanical polishing and slow polishing speed and poor surface flatness caused by chemical polishing, making the material removal rate more uniform.

[0019] Preferably, in step S9, the second portion is removed by a stripping process.

[0020] By adopting the above technical solution, the second part is completely removed by the dissolving liquid, which can improve the convenience of removing the second part and make the second part removed more thoroughly.

[0021] Preferably, during the process of removing the second portion by the stripping process, the dissolving liquid is stirred to increase the turbulence of the dissolving liquid.

[0022] By adopting the above technical solution, the increase in the turbulence of the solution will significantly improve the mass transfer efficiency of the reactants and products in the solution. The turbulent mixing effect can break the boundary layer near the surface of the object, allowing the solution to reach the surface of the object more quickly and accelerate the diffusion of the dissolved products.

[0023] Preferably, after the second portion is removed by a stripping process, ionized water is used to clean the second substrate and the functional layer film.

[0024] By adopting the above technical solution, the second substrate and the functional layer film are rinsed with ionized water to ensure the cleanliness of the second substrate and the functional layer film.

[0025] In summary, the present application includes at least one of the following beneficial technical effects: 1. After the buffer layer is completely removed, when the buffer layer is removed by CMP wet polishing, the functional layer film is polished and ground. Since the second part is filled in the groove, the shape mutation of the functional layer film is reduced, and the stress concentration at the edge of the functional layer film is reduced, which can effectively avoid the occurrence of breakage at the edge of the functional layer film during polishing, and improve the yield rate of the ultra-thin functional layer structure of the composite substrate; 2. Use the dissolving liquid to dissolve and remove the target object, improve the convenience of removing the first part, control the downward movement of the first substrate, control the depth of the second part immersed in the dissolving liquid, and then control the removal amount of the second part, thereby improving the accuracy and convenience of controlling the removal amount of the second part; 3. By using a stripping process to completely remove the first portion and partially remove the second portion, the thickness of the second portion is made smaller than the depth of the groove. When the second portion expands due to heating, the second portion will not exceed the groove, thereby effectively avoiding the influence of the thermal expansion of the second portion on the bonding of the functional layer film and improving the bonding effect between the functional layer film and the second substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a method for preparing a novel composite substrate ultra-thin functional layer structure according to Example 1 of the present application.

[0027] Figure 2 It is a schematic diagram of the structure of growing a buffer layer and an ultra-thin functional layer on a first substrate.

[0028] Figure 3 It is a schematic diagram of the structure of patterning an ultra-thin functional layer to form an independent functional layer film.

[0029] Figure 4 It is a schematic diagram of the structure of applying photoresist in the groove to form a temporary supporting layer.

[0030] Figure 5 It is a structural schematic diagram of removing the redundant part of the temporary supporting layer.

[0031] Figure 6 It is a schematic diagram of the structure of bonding the second substrate to the ultra-thin functional layer on the first substrate.

[0032] Figure 7 It is a schematic diagram of the structure for thinning and removing the first substrate.

[0033] Figure 8 It is a schematic diagram of the structure with the buffer layer removed.

[0034] Fig. 9 It is a schematic diagram of the structure in which the temporary support layer is dissolved and removed by the dissolving liquid.

[0035] Fig.10It is a schematic structural diagram of the thinned temporary support layer in the preparation method of Example 2 of the present application.

[0036] Fig.11 It is a structural schematic diagram of removing the redundant part of the temporary support layer in Example 2 of the present application.

[0037] Fig.12 It is a schematic diagram of the structure of bonding the second substrate to the ultra-thin functional layer on the first substrate in Example 2 of the present application.

[0038] Explanation of the accompanying drawings: 1. first substrate; 2. buffer layer; 3. ultra-thin functional layer; 31. functional layer film; 4. temporary supporting layer; 41. first part; 42. second part; 5. second substrate. DETAILED DESCRIPTION

[0039] The following is combined with Figure 1-12 This application is described in further detail.

[0040] The embodiment of the present application discloses a method for preparing a novel composite substrate ultra-thin functional layer structure.

[0041] Example 1 Reference Figure 1 , Figure 2 , a novel method for preparing an ultra-thin functional layer structure of a composite substrate comprises: S1. Epitaxially growing a buffer layer 2 and an ultra-thin functional layer 3 structure that are substantially lattice-matched on a first substrate 1 in sequence.

[0042] The first substrate 1 is a 6-inch 650 μm thick single crystal Si substrate, on which a 200 nm AlN buffer layer (buffer layer 2) and a 2 μm GaN HEMT ultra-thin functional layer (ultra-thin functional layer 3) are sequentially grown by MBE epitaxial growth.

[0043] S2, reference Figure 3 , the ultra-thin functional layer 3 on the first substrate 1 is patterned and divided into independent functional layer films 31 located on the surface of the first substrate 1 .

[0044] On the surface of the ultra-thin functional layer 3 after epitaxy, AZ701 photoresist is used for exposure, and the ultra-thin functional layer 3 of 2 μm is etched in a chlorine-based atmosphere, and the etching stops at the surface of the AlN buffer layer 2, and the ultra-thin functional layer 3 is divided into island structures (functional layer films 31) with a size of 1 cm×1 cm and an interval of 20 μm, thereby obtaining a patterned Si-based GaN HEMT wafer.

[0045] S3. Reference Figure 4 , photoresist is coated in the grooves between the functional layer films 31 , and the photoresist is solidified to form a temporary supporting layer 4 .

[0046] The composition of the photoresist in this embodiment is polyimide, and the photolithography will be coated in the groove by spin coating. The specific process is as follows: 1. Before spin coating, the surface of the functional layer structure needs to be cleaned to remove surface oxides, dirt and impurities; 2. A small amount of photoresist (usually a few milliliters) is dropped on the center of the functional layer film 31. The dispensing can be performed when the functional layer film 31 is stationary (static spin coating) or when the functional layer film 31 is already rotating (dynamic spin coating); 3. The first substrate 1 is driven to rotate, and the photoresist is Under the action of centrifugal force, it spreads to the groove and the functional layer film 31, and forms a 2μm film on the upper surface of the functional layer film 31; 4. During the rotation process, the solvent in the photoresist will gradually evaporate, causing the film to become further thinner and stable; 5. After coating is completed, the functional layer structure usually needs to be soft-baked to remove excess solvent and enhance the adhesion of the photoresist. After baking, a temporary support layer 4 is formed on the buffer layer 2. At this time, the temporary support layer 4 includes a first portion 41 coated on the functional layer film 31 and a second portion 42 located in the groove.

[0047] The photoresist is spin-coated into the groove, and a temporary support layer 4 is formed on the buffer layer 2 after baking, so that the temporary support layer 4 has high uniformity. By adjusting the spin coating speed, time and viscosity of the photoresist, the film thickness can be accurately controlled to meet different process requirements.

[0048] S4. Reference Figure 5 , remove the first portion 41 on the functional layer film 31, and in this embodiment, the thickness of the second portion 42 is equal to the thickness of the functional layer film 31. The first portion 41 is removed by polishing and grinding, specifically, the temporary first portion 41 is polished and removed by using CMP wet polishing technology, so that the surface of the temporary support layer 4 is flush with the surface of the functional layer film 31.

[0049] The first portion 41 will hinder the bonding between the ultra-thin functional layer 3 and the second substrate 5. For this reason, the first portion 41 is removed by polishing and grinding, so that the surface of the second portion 42 is coplanar with the surface of the functional layer film 31, thereby effectively avoiding the influence of the first portion 41 on the bonding of the functional layer film 31 and ensuring the bonding effect between the functional layer film 31 and the second substrate 5.

[0050] S5, respectively, perform activation treatment and cleaning process on the surface of the second substrate 5 and the functional layer film 31 on the first substrate 1. In this embodiment, the second substrate 5 is a 6-inch single crystal SiC wafer with a thickness of 500 μm, and the surface of the second substrate 5 and the surface of the functional layer film 31 are respectively subjected to Ar ion activation treatment, the activation process is Ar ion beam current 200 sccm, processing time 30 s, activation power 50 W, and then the second substrate 5 and the Si-based ultra-thin functional layer 3 are respectively cleaned by deionized water megasonic cleaning.

[0051] S6. Reference Figure 6 , the surfaces of the second substrate 5 and the functional layer film 31 grown on the first substrate 1 are placed opposite to each other and put into a bonding machine for bonding. The processed second substrate 5 and the functional layer film 31 on the first substrate 1 are placed face to face in a bonding machine for bonding, the bonding temperature is 200°C, the bonding pressure is 30000N, and the bonding time is 1h (the warpage after bonding is less than 20μm, and the wafer can be taped out normally).

[0052] S7, reference Figure 7 , the bonded composite substrate structure is thinned from the direction of the first substrate 1 until it is completely removed. The removal process is as follows: 1. The bonded composite structure is placed in a grinder for grinding and thinning, and the first substrate 1 is thinned until about 100μm remains, and the grinding rate is about 10μm / min; 2. The remaining first substrate 1 is completely removed by dry etching with fluorine-based gases such as SF6 to expose the surface of the buffer layer 2.

[0053] S8. Reference Figure 8 , the buffer layer 2 is thinned and completely removed by CMP wet polishing. The 200nm buffer layer 2 is completely removed to obtain a composite substrate structure consisting of a 6-inch SiC-based wafer and a GaN HEMT functional layer with a thickness of 2μm bonded and transferred to the surface of the SiC wafer. The specific process of CMP wet polishing is: 1. Chemical reaction stage A polishing liquid that can chemically react with the surface of the buffer layer 2 is selected. The chemical substances in the polishing liquid chemically react with the material of the buffer layer 2 to convert insoluble substances into soluble substances or soften high-hardness substances.

[0054] 2. Mechanical grinding stage The polishing head presses the buffer layer 2 onto the rotating polishing pad with a certain pressure, and a thin film of grinding liquid is formed between the polishing pad and the surface of the buffer layer 2.

[0055] The abrasive particles in the grinding liquid are evenly distributed under the transmission of the polishing pad and the action of centrifugal force, and mechanically rub against the surface of the buffer layer 2 to remove the easily removable substances generated by the chemical reaction.

[0056] 3. Cyclic process Chemical reaction and mechanical grinding are performed alternately to continuously remove excess material on the surface of the buffer layer 2 until the desired flatness is achieved.

[0057] By utilizing the dissolution and softening effect between the polishing liquid and the buffer layer 2, the global planarization capability of the surface of the buffer layer 2 can be improved, and high precision and high flatness of the grinding of the buffer layer 2 can be achieved. At the same time, the difference in removal rate between hard materials and soft materials is minimized to the greatest extent, avoiding the problems of surface damage caused by simple mechanical polishing and slow polishing speed and poor surface flatness caused by chemical polishing, so that the material removal rate is more uniform.

[0058] S9, reference Fig. 9 , the second portion 42 is corroded and dissolved by a dissolving liquid, and the second portion 42 is removed. The dissolving liquid in this embodiment is dimethyl sulfoxide (DMSO), which can dissolve polyimide, but cannot effectively dissolve SiC and GaN. Therefore, when removing the second portion 42, the functional layer structure is immersed in a container filled with the dissolving liquid. When the dissolving liquid completely dissolves and removes the second portion 42, the dissolving liquid is extracted from the functional layer structure, and the functional layer structure is cleaned with deionized water. The functional layer structure is rinsed with ionized water to ensure the cleanliness of the surface of the functional layer structure.

[0059] In order to increase the dissolution rate of the temporary support layer 4 by the solution, the solution is stirred by a stirring device, and the specific stirring device can be one of a blade stirrer, a turbine stirrer, a paddle stirrer, an anchor stirrer, and a ribbon stirrer. The stirring device is used to increase the turbulence of the solution, and the increase in the turbulence will significantly improve the mass transfer efficiency of the reactants and products in the solution. The turbulent mixing effect can break the boundary layer near the surface of the object, so that the solution reaches the surface of the object more quickly, and accelerates the diffusion of the dissolved product.

[0060] S10, obtaining a functional layer film 31 on the target second substrate 5.

[0061] The implementation principle of Example 1 is: when the buffer layer 2 is completely removed and the functional layer film 31 is ground, the groove is filled with the second portion 42, thereby reducing the shape mutation of the functional layer film 31 and the stress concentration at the edge of the functional layer film 31. This can effectively avoid the edge of the functional layer film 31 from being broken during polishing, thereby improving the yield of the ultra-thin functional layer structure of the composite substrate.

[0062] Example 2 Reference Fig.10 , Fig.11 and Fig.12The difference between this embodiment and embodiment 1 is that when the functional layer film 31 is bonded to the second substrate 5, the temperature needs to be increased during the bonding process. The second portion 42 will expand as the temperature rises. The expansion will cause the surface of the second portion 42 to exceed the surface of the functional layer film 31, thereby affecting the bonding between the functional layer film 31 and the second substrate 5. For this reason, in step S4, a stripping process is used to completely remove the first portion 41 and partially remove the second portion 42, so that the thickness of the second portion 42 is less than the thickness of the functional layer film 31.

[0063] Reference Fig.10 , Fig.11 and Fig.12 The specific peeling process is as follows: the first substrate 1 is mounted on the mounting seat of the feeding device, and then the surface of the functional layer film 31 is kept level with the liquid surface of the dissolving solution, and then the feeding device drives the second part 42 to immerse in the dissolving solution, and specifically immerses it to 1 / 3 of the second part 42. After being dissolved and corroded by the dissolving solution, the second part 42 has 2 / 3 of the entire thickness remaining. By completely removing the first part 41 and partially removing the second part 42, the thickness of the second part 42 is made smaller than the functional layer film 31, so that when the second part 42 is heated and expanded, it will not exceed the groove, effectively avoiding the influence of the thermal expansion of the second part 42 on the bonding of the functional layer film 31, and improving the bonding effect between the functional layer film 31 and the second substrate 5.

[0064] Specifically, the feeding device is a ball screw feeding system. The ball screw achieves high-precision micro-feeding through the rolling motion of steel balls, and can achieve a pulse feeding accuracy of 0.1μm. The feeding device is used to control the depth of the temporary support layer 4 immersed in the dissolving solution, thereby adjusting the thickness of the remaining part of the second part 42 in the groove, thereby improving the convenience and accuracy of controlling the thickness of the second part 42.

[0065] In order to facilitate observation of the depth of the second part 42 immersed in the dissolving liquid, the operator observes the depth of the second part 42 immersed in the dissolving liquid through the microscope magnification system, and adjusts the feeding amount of the feeding device according to the display result of the microscope magnification system. Specifically, the microscope magnification system includes but is not limited to an optical microscope magnification system and a super-depth 3D digital microscope. The microscope magnification system is used to observe the depth of the second part 42 immersed in the dissolving liquid, so as to facilitate timely control of the depth of the second part 42 immersed in the dissolving liquid and accurately control the thickness of the second part 42 in the groove.

[0066] After the second portion 42 is removed, the functional layer film 31 is taken out from the dissolving solution, and then the surfaces of the functional layer film 31 and the buffer layer 2 are cleaned with ionized water to ensure that the surfaces of the functional layer film 31 and the buffer layer 2 are clean.

[0067] The implementation principle of Example 2 is: the first part 41 is completely removed and the second part 42 is partially removed by the dissolving liquid, so that the thickness of the second part 42 is less than the depth of the groove, so that when the second part 42 is heated and expanded, the second part 42 will not exceed the groove, effectively avoiding the influence of the thermal expansion of the second part 42 on the bonding of the functional layer film 31, and improving the bonding effect between the functional layer film 31 and the second substrate 5.

[0068] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a novel composite substrate ultra-thin functional layer structure, characterized in that: The method comprises the following steps: S1, epitaxially growing in sequence a buffer layer (2) and an ultra-thin functional layer (3) structure lattice-matched with the first substrate (1) on the first substrate (1); S2, patterning an ultra-thin functional layer (3) on a first substrate (1), wherein the ultra-thin functional layer (3) is divided into functional layer films (31) that are independent of each other and are located on a surface of the first substrate (1); S3, coating photoresist in the grooves between the functional layer films (31), and solidifying the photoresist into a temporary support layer (4); S4, removing the first portion (41) of the temporary support layer (4) on the functional layer film (31) to reduce the thickness of the temporary support layer (4), wherein the second portion (42) of the temporary support layer (4) is located in the groove between the functional layer films (31) and does not cover the upper surface of the functional layer film (31); S5, performing activation treatment and cleaning process, respectively treating the bonding surface of the target second substrate (5) and the upper surface of the functional layer film (31) on the first substrate (1); S6, forming a bonding surface of the second substrate (5) as a bonding target and an upper surface of the first substrate (1) having the functional layer film (31); S7, removing the first substrate (1) to expose the buffer layer (2); S8, removing the buffer layer (2) to expose the lower surface of the functional layer film (31), wherein the buffer layer (2) is removed by CMP wet polishing; S9, removing the temporary support layer (4) to expose the grooves between the functional layers, wherein the functional layer film (31) is bonded to the second substrate (5), and the grooves reveal the side walls of the functional layer film (31).

2. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 1, characterized in that: In step S3, the photoresist is applied into the groove by spin coating. A small amount of the photoresist is first dropped on the center of the ultra-thin functional layer (3). The first substrate (1) is then rotated. The photoresist is spread onto the groove and the functional layer film (31) under the action of centrifugal force. The photoresist is then baked to form a temporary support layer (4) located on the buffer layer (2).

3. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 1, characterized in that: In step S4, the first portion (41) is removed by polishing and grinding, and the polishing and grinding starts from the upper surface of the first portion (41) and stops at the upper surface of the functional layer film (31), so that the surface of the second portion (42) is flush with the surface of the functional layer film (31).

4. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 1, characterized in that: In step S4, the first portion (41) is removed by a stripping process, and the second portion (42) is thinned by a stripping process, so that the upper surface of the second portion (42) is closer to the buffer layer (2) than the upper surface of the functional layer film (31).

5. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 4, characterized in that: The stripping process includes: adjusting the upper surface of the first part (41) to be parallel to the liquid surface of the dissolving solution, moving the first substrate (1) downward, immersing the first part (41) in the dissolving solution, and partially immersing the second part (42) in the dissolving solution, so that the first part (41) is completely removed and the second part (42) is partially removed.

6. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 5, characterized in that: During the stripping process, the process of immersing the first portion (41) and the second portion (42) in the dissolving solution is observed through a microscope magnification system, and an operator adjusts the immersion amount of the first portion (41) and the second portion (42) through the display of the microscope magnification system.

7. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 1, characterized in that: In step S8, the CMP wet polishing includes: first selecting a polishing liquid that can chemically react with the surface of the buffer layer (2), wherein the chemical reaction can convert the insoluble matter of the buffer layer (2) into a soluble matter or soften the high-hardness substance, and then using a polishing head to press the buffer layer (2) onto the polishing pad and drive the buffer layer (2) to rotate, so that the abrasive particles in the grinding liquid and the buffer layer (2) produce mechanical friction, thereby removing the buffer layer (2).

8. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 1, characterized in that: In step S9, the second portion (42) is removed by a stripping process.

9. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 8, characterized in that: During the process of removing the second portion (42) by a stripping process, the dissolving liquid is stirred to increase the turbulence of the dissolving liquid.

10. The method for preparing the novel composite substrate ultra-thin functional layer structure according to claim 8, characterized in that: After the second portion (42) is removed by a stripping process, the second substrate (5) and the functional layer film (31) are cleaned using ionized water.

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