A substrate stripping method based on laminated mask substrate

Abstract

The present invention relates to a substrate stripping method based on a laminated mask substrate. The method comprises: 1) using MOCVD technology to grow a III-nitride material on a three-dimensional laminated mask substrate to form a III-nitride material thin film; 2) using HVPE technology to grow a III-nitride material on the continuous thin film to form a III-nitride material thick film; 3) generating stress between the three-dimensional laminated mask substrate and the III-nitride material thick film by cooling, thereby achieving self-separation. The method of the present invention can be self-separated from the substrate during the cooling process due to its weak connection with the substrate, avoiding the use of expensive technologies such as laser stripping, saving process steps and time, significantly improving production yield, and improving product quality; the specially made three-dimensional laminated mask substrate can cooperate with MOCVD to grow a high-quality thin film, and then can epitaxially grow a high-crystal quality thick film through HVPE.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors, and in particular relates to a substrate stripping method based on a stacked mask substrate. Background Art

[0002] After nearly two or three decades of research, III-nitride materials such as GaN, AlN, InN, AlGaN, and InGaN, as third-generation semiconductors, have shown many excellent physical and chemical properties and have been considered to be semiconductor materials with very high application value. Since the single crystal growth of III-nitride materials is very difficult, HVPE is a commonly used method in the growth technology of self-supporting single crystal III-nitride materials. HVPE is the abbreviation of Hydride Vapor Phase Epitaxy, which refers to the hydride vapor phase epitaxy technology. There are two main problems in the preparation of self-supporting thick films of III-nitrides by HVPE: First, the heterogeneous epitaxy causes severe warping of the III-nitride thick film; second, how to separate the epitaxial III-nitride thick film from the substrate. The first problem originates from stress. Since there is a large lattice mismatch and thermal mismatch between III-nitride materials and the commonly used substrate materials sapphire and silicon, stress will accumulate as the thickness increases due to lattice mismatch during the growth process, and stress will further accumulate during the cooling process due to the different thermal expansion coefficients with the substrate material. Therefore, for thick-film III-nitrides, due to excessive stress, severe warping will occur, and even the entire film will break, which seriously reduces the HVPE preparation yield in industrial production. For the mass production of self-supporting thick films of III-nitrides using HVPE technology, the first problem that needs to be solved is the warping problem. The second problem is the peeling of the III-nitride material from the substrate. Since III-nitrides are tightly bonded to the substrate, they are very difficult to peel off. For this reason, the industry has developed a variety of peeling methods, such as laser peeling.

[0003] Taking GaN as an example, the existing technology has the following main disadvantages:

[0004] (1) The existing methods for growing self-supporting GaN single crystals mainly include the ammonothermal method, the sodium-sulfur method and the HVPE method. Among them, the ammonothermal method and the sodium-sulfur method have relatively slow growth rates, so that the production cost remains high, and a high-pressure environment is required, and the equipment has a high risk factor. Although the HVPE method has a faster growth rate, the yield is very low, less than 20%. Most of them break during the cooling process. Even those that do not break are very difficult to peel off from the substrate. After peeling, the GaN film is warped and the lattice is twisted due to excessive stress during growth on the substrate. After being polished by the CMP process, the crystal orientation of the surface is not consistent, and there are many subsequent problems when using it as a substrate.

[0005] (2) In other technical solutions that achieve easy separation through porous structures or nanowire padding, because GaN is not grown on a regular lattice-matched substrate, the quality of the early MOCVD layer growth is not high. Therefore, the HVPE technology is used to epitaxially thicken the film. Although the defect density is reduced, the degree of reduction is limited, resulting in low overall crystal quality of the thick film product grown, which also leads to low use value.

[0006] (3) The technology of growing the first layer of GaN film using a patterned substrate or ordinary lateral epitaxy technology. Since ordinary patterned substrates or lateral epitaxy technology have a large number of concentrated dislocations in the window area, the overall crystal quality has improved, but the degree of improvement is limited. And because the wing area of ​​ordinary lateral epitaxy will be raised, a large number of defects will inevitably be generated in the closed area, including dislocations, voids and other defects, which seriously affect the overall quality. Only the crystal quality in the local area has been improved. These high-density defect areas will reduce the device performance when epitaxial devices are grown, so such technology still cannot fully meet the needs of the industry. Summary of the invention

[0007] The purpose of the present invention is to solve the problem that the thick film of group III nitride grown by HVPE technology is fragile and difficult to be peeled off from the substrate.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A substrate stripping method based on a laminated mask substrate comprises the following steps:

[0010] 1) using MOCVD technology to grow a III-nitride material on a three-dimensional stacked mask substrate to form a III-nitride material film;

[0011] 2) growing a group III nitride material on the continuous film using HVPE technology to form a group III nitride material thick film;

[0012] 3) Stress is generated between the three-dimensional stacked mask substrate and the III-nitride material thick film by cooling, thereby achieving self-separation.

[0013] Furthermore, in step 1), the thickness of the III-nitride material film is 1 to 20 microns.

[0014] Furthermore, in step 2), the thickness of the III-nitride material thick film is 20 to 500 microns.

[0015] Furthermore, for the group III nitride material thick film after self-separation, a self-supporting stress-free single crystal wafer is obtained through a surface planarization process.

[0016] Furthermore, in step 1), the three-dimensional stacked mask substrate comprises a substrate, on which a bottom mask layer and a top mask layer are sequentially arranged; the bottom mask layer is provided with periodically distributed windows, and the symmetry of the pattern of the windows in the plane is consistent with the crystal symmetry of the hexagonal III-nitride material or is a subset thereof; the pattern of the windows of the top mask layer is the same as that of the bottom mask layer, and the positions of the windows are staggered; the top mask layer is connected to the bottom mask layer through a dielectric layer.

[0017] Furthermore, the shape of the window is one of the following: a bar, an equilateral triangle, or a regular hexagon.

[0018] Furthermore, the top mask layer and the bottom mask layer are SiN x , the dielectric layer is SiO2.

[0019] Further, step 1) comprises:

[0020] a) In the low-temperature nucleation stage, III-nitride nucleation points are formed on the substrate surface exposed by the bottom mask window, and the III-nitride begins to form island-like structure atomic clusters with these nucleation points as the center;

[0021] b) increasing the temperature and growing the III-nitride under normal III-nitride growth parameter conditions, and as time goes by, the grown III-nitride drills out of the channel, exposing the top mask window and forming a protruding shape;

[0022] c) After the trench is drilled and a certain height is formed outside the top window, the growth parameters are switched and MOCVD lateral epitaxial growth technology is used to make the lateral growth rate much greater than the vertical growth rate. The growth continues in this way until the III-nitride is closed into a flat large plane, that is, a III-nitride film is formed.

[0023] Furthermore, in step 3), laser lift-off technology is used to assist in substrate lift-off.

[0024] Furthermore, the III-group nitride material is GaN, AlN, InN or a ternary or quaternary alloy formed thereof.

[0025] Compared with the prior art, the present invention has the following two significant advantages:

[0026] 1. Due to the weak connection with the substrate, it can be separated from the substrate during the cooling process, avoiding the use of expensive technologies such as laser stripping to separate the III-nitride thick film from the substrate. Since the III-nitride thick film can be separated from the substrate without the need for laser stripping and other steps, it not only saves process steps and time, but also greatly improves the production yield. There is no crystal distortion, and there is no need to use a flattening process to flatten the already warped crystal; it not only effectively reduces the overall cost, but also improves product quality. This is the key point for the large-scale application of high-quality homogeneous substrates of III-nitrides.

[0027] 2. Since the specially made three-dimensional stacked mask substrate can cooperate with MOCVD to grow high-quality thin films, as a pre-process step of HVPE, it will be possible to epitaxially grow thick films with high crystal quality through HVPE. Taking GaN material growth as an example, the present invention can prepare GaN with a dislocation density of 10 at a relatively low cost. 5 / cm 2 The self-supporting GaN substrate is significantly superior to other existing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of stress distortion of self-supporting thick films of group III nitride grown on a planar substrate, where (a) is compressive stress distortion and (b) is tensile stress distortion.

[0029] Figure 2 It is a schematic diagram of the self-separation principle of growing thick-film III-nitride using the special three-dimensional stacked mask substrate of the present invention.

[0030] Figure 3 This is a picture of the effect of a 20-micron thick GaN thick film self-separating from a special laminated mask substrate during the cooling process observed under a microscope.

[0031] Figure 4 It is a schematic diagram of a three-dimensional structure of a strip substrate, wherein: 1-top mask layer, 2-substrate, 3-top window, 4-bottom window, 5-bottom mask layer, 6-medium layer connecting the top mask layer and the bottom mask layer.

[0032] Figure 5 These are figures with the same symmetry as the gallium nitride crystal structure, where (a), (b), and (c) are bars, triangles, and hexagons, respectively.

[0033] Figure 6 It is a schematic plan view of the design of strip, triangle and hexagonal graphic substrates, wherein (a), (b) and (c) represent strip, triangle and hexagonal windows respectively, the dotted line represents the lower window and the solid line represents the upper window.

[0034] Figure 7The following are scanning electron microscope images of GaN grown on substrates with different patterns, where (a), (b), and (c) represent the scanning electron microscope images of GaN grown on substrates with triangular, hexagonal, and stripe patterns, respectively. The figure shows the intermediate state of growth, and continued growth will form a closed film. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below through specific embodiments and drawings.

[0036] The purpose of the present invention is to solve the problem that the thick film of group III nitride grown by HVPE technology is fragile and difficult to peel off from the substrate. By using the substrate and growth process mentioned in the present invention, the self-separation of the complete group III nitride thick film from the substrate will be achieved, the production yield will be improved, and a high-quality self-supporting single crystal group III nitride thick film will be obtained. Because the high-quality self-supporting group III nitride single crystal substrate has no lattice mismatch and thermal mismatch with the epitaxially grown group III nitride layer to be used for device preparation, the crystal quality of the epitaxial layer will be greatly improved, so that the performance of the device is closer to the theoretical limit of the material, the performance is improved, and the device life is extended, so it is the best choice for epitaxial growth of high-quality devices. However, it is difficult to prepare high-quality self-supporting group III nitride single crystal substrates at present, mainly because the yield is low, the cost is high, and it takes a long time. The important purpose of the present invention is to improve the preparation yield of group III nitride self-supporting thick films, reduce costs, improve crystal quality and process stability, and provide raw material supply for group III nitride related industries.

[0037] like Figure 1 As shown in the figure, the traditional method of growing III-nitride thick films will cause the substrate and film to warp due to excessive stress. During the cooling process, thermal stress exacerbates the warping, causing cracks or even shattering of the film. Even if the thick film material is peeled off with the help of laser lift-off technology, it still needs to go through a grinding process, and only the surface is ground, and the lattice distortion problem still exists, resulting in low quality of the thick film. It is difficult to obtain a complete large piece of high-quality self-supporting III-nitride thick film because the yield is very low.

[0038] In the present invention, a special three-dimensional laminated mask substrate is used, and the growth method is divided into two steps. First, the group III nitride material is grown on the mask substrate using MOCVD equipment / technology to form a high-quality continuous film with a thickness of 1 to 20 microns. On this basis, the group III nitride is grown using HVPE technology, and the growth rate of the group III nitride film is accelerated by its advantage of fast growth rate, and a group III nitride thick film with a thickness of 20 to 500 microns is grown. MOCVD can directly grow high-quality group III nitrides on substrates such as sapphire or silicon, but the growth rate is slow. It is difficult for HVPE to directly grow high-quality group III nitride single crystals on substrates such as sapphire and silicon, but it can grow high-quality single crystals on group III nitride layers, and the growth rate is fast. Therefore, the group III nitride thick film growth step is generally divided into two steps, so that high-quality crystals can be obtained. Due to the special structure of the mask substrate, the mask layer and the III-nitride do not form chemical bonds, but rely on weak van der Waals forces to bond, so that the direct connection between the III-nitride film and the substrate is very small, and it will break under huge stress. During the growth process, due to the high temperature of the growth conditions, the thermal stress between the substrate and the thick film will not be reflected. During the cooling process, due to the large difference in thermal expansion coefficients between the substrate and the III-nitride thick film, huge stress will be generated, thereby breaking the weakest channel connection, thereby achieving a self-separation effect, such as Figure 2 shown.

[0039] For the thick-film III-nitride after self-separation, after the surface planarization process, a self-supporting stress-free single crystal wafer can be obtained, which can be used for various research and device production in the III-nitride related industry.

[0040] Figure 3 The experimental results show the self-separation effect, but because the film is not thick enough, it cannot be self-supporting after self-separation and is easy to break. It is only necessary to optimize the growth conditions to make the surface flat, and then use HVPE technology to thicken the film, so that the film can maintain its integrity after self-separation.

[0041] The key point of the present invention is to use a special three-dimensional laminated mask substrate to grow a self-separating III-nitride thick film. The use of a special three-dimensional laminated mask substrate is the most critical point, because the substrate can not only weaken the direct connection strength between the film and the substrate, achieving the effect of easy peeling, but also maintain a very high crystal quality when the initial film layer is grown by MOCVD, which makes the overall crystal quality of the film epitaxially thickened by the HVPE method very high, and the dislocation density can be less than 10 5 / cm 2 .

[0042] Figure 4 Schematic diagram of the structure of the special three-dimensional laminated mask substrate of the present invention. The top mask layer 1 and the bottom mask layer 5 located on the substrate 2 are both provided with periodically distributed strip windows, namely the top window 3 and the bottom window 4, but staggered with each other. The top mask layer 1 and the bottom mask layer 5 are connected by a dielectric layer 6. The materials of the top mask layer 1 and the bottom mask layer 5 can be SiN x , etc. The material of the dielectric layer 6 can be SiO2, etc.

[0043] Among them, the bottom mask layer is provided with periodically distributed special graphic windows. Figure 4 In addition to the strips in the figure, it can also be regular triangles and regular hexagons, such as Figure 5 As shown. These patterns are the patterns whose symmetry in the plane is consistent with the crystal symmetry of GaN and other III-nitride materials or a subset thereof. Using these patterns with special symmetry, it is possible to prepare a continuous and flat high-quality epitaxial GaN and other III-nitride thin films covering the entire substrate surface, which can be more fully compatible with subsequent device processes. The patterns of the top mask layer and the bottom mask layer are the same, but they are staggered, such as Figure 6 As shown, the dotted line represents the lower window and the solid line represents the upper window.

[0044] The growth process of group III nitride on the 3D stacked mask substrate structure of the present invention is as follows:

[0045] 1) At the beginning, it is necessary to go through a low-temperature nucleation stage, during which group III nitride nucleation points are formed on the substrate surface exposed by the bottom mask window. With these points as the center, group III nitride begins to form island-like structure atomic clusters.

[0046] 2) Then, the temperature is raised and the III-nitride is grown under normal III-nitride growth parameter conditions. As time goes by, the grown III-nitride will drill out the channel, exposing the top mask window and forming a protruding shape.

[0047] 3) After the trench is drilled and a certain height is formed outside the top window, the growth parameters are switched and a lateral epitaxial growth technique (such as the MOCVD lateral epitaxial growth technique described above in the present invention) is used to make the lateral growth rate much greater than the vertical growth rate. The growth continues in this way until the III-nitride is closed into a flat large plane, i.e., the III-nitride film described above in the present invention is formed.

[0048] Figure 7 This is a scanning electron microscope image of gallium nitride grown on substrates with different patterns. The image shows the intermediate state of growth. Continuing growth will form a closed film.

[0049] In the traditional method of growing III-nitride thick films on planar substrates, in addition to being easy to break, laser stripping technology is also required to separate the III-nitride thick film from the substrate. The technical difficulty of laser stripping itself is also very high, which further reduces the yield and consumes a long time for the process, so the cost is relatively high. The beneficial effect brought by the present invention is that the effect of separating the III-nitride thick film from the substrate can be achieved without the laser stripping step, which not only saves process steps and time, but also greatly improves the production yield. It is expected that the yield of the stripped thick film will exceed 90%, and there will be no crystal distortion. Not only the overall cost is greatly reduced, but also the product quality is improved. This will be the key point for the large-scale application of high-quality homogeneous substrates of III-nitrides. Once high-quality homogeneous III-nitride substrates are widely used, many long-standing industry problems will be solved, and the performance of the produced devices will be greatly improved. In the field of power electronic devices, the withstand voltage of the device can be improved, and the heat loss of the device itself can be reduced. In the field of radio frequency devices, the power density and radio frequency conversion efficiency can be improved, the operating voltage can be reduced, and the frequency application range can be expanded. In the field of optoelectronic devices, vertical structure devices can be made to greatly improve the luminous efficiency and reduce the complexity of the driving circuit.

[0050] At present, some existing technologies can produce a self-peeling effect. For example, nanowires are laid on a flat substrate to weaken the connection strength between the growing III-nitride film and the substrate, thereby achieving an easy peeling effect. There is also a method that first prepares a porous III-nitride on a flat substrate to weaken the connection strength between the substrate and the film. There is also a method that uses an ordinary patterned substrate for growth, which is also to weaken the connection strength between the substrate and the gallium nitride film to achieve an easy peeling effect. However, since the quality of some III-nitride films before using the HVPE technology is not high, the quality of the thick film crystals finally epitaxially grown by HVPE is also not high. Taking the growth of GaN materials as an example, an ordinary patterned substrate can make the overall dislocation density close to 10 6 / cm 2 However, due to the unevenness, the defect density in the concentrated area is still very high. However, through the technology of the present invention, it is possible to prepare a material with a dislocation density of less than 10 5 / cm 2 The self-supporting GaN substrate is significantly superior to other existing methods.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. A person skilled in the art may modify or make equivalent substitutions for the technical solutions of the present invention without departing from the principle and scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A substrate stripping method based on a laminated mask substrate, characterized in that: The following steps are involved: 1) using MOCVD technology to grow a group III nitride material on a three-dimensional stacked mask substrate to form a group III nitride material film; the group III nitride material film has a thickness of 1 to 20 microns; 2) using HVPE technology to grow a group III nitride material on the group III nitride material thin film to form a group III nitride material thick film; the thickness of the group III nitride material thick film is 20 to 500 microns; 3) Stress is generated between the three-dimensional stacked mask substrate and the thick film of the group III nitride material by cooling, thereby achieving self-separation; Step 1) The three-dimensional stacked mask substrate comprises a substrate, on which a bottom mask layer and a top mask layer are sequentially arranged; the bottom mask layer is provided with periodically distributed windows, and the symmetry of the pattern of the windows in the plane is consistent with the crystal symmetry of the hexagonal group III nitride material or is a subset thereof; the pattern of the windows of the top mask layer is the same as that of the bottom mask layer, and the positions of the windows are staggered; the top mask layer is connected to the bottom mask layer through a dielectric layer; The graphics of the window are a triangular window and a hexagonal window as shown in (b) and (c) of FIG. 6 , wherein the dotted line represents the lower layer window and the solid line represents the upper layer window.

2. The method according to claim 1, characterized in that For the thick film of the group III nitride material after self-separation, a self-supporting stress-free single crystal wafer is obtained through a surface planarization process.

3. The method according to claim 1, characterized in that The top mask layer and the bottom mask layer are SiN x , the dielectric layer is SiO2.

4. The method according to claim 1, characterized in that: Step 1) includes: a) In the low-temperature nucleation stage, III-nitride nucleation points are formed on the substrate surface exposed by the bottom mask window, and the III-nitride begins to form island-like structure atomic clusters with these nucleation points as the center; b) increasing the temperature and growing the III-nitride under normal III-nitride growth parameter conditions, and as time goes by, the grown III-nitride drills out of the channel, exposing the top mask window and forming a protruding shape; c) After the trench is drilled and a certain height is formed outside the top window, the growth parameters are switched and MOCVD lateral epitaxial growth technology is used to make the lateral growth rate much greater than the vertical growth rate. The growth continues in this way until the III-nitride is closed into a flat large plane, that is, a III-nitride film is formed.

5. The method according to claim 1, characterized in that Step 3) using laser lift-off technology to assist in substrate lift-off.

6. The method according to claim 1, characterized in that The group III nitride material is GaN, AlN, InN or a ternary or quaternary alloy thereof.

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