CN112301422A - Substrate stripping method based on laminated mask substrate - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 66
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- 229910004205 SiNX Inorganic materials 0.000 claims description 3
- 229910052681 coesite Inorganic materials 0.000 claims description 3
- 229910052906 cristobalite Inorganic materials 0.000 claims description 3
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- 229910052682 stishovite Inorganic materials 0.000 claims description 3
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- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/04—Pattern deposit, e.g. by using masks
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/01—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes on temporary substrates, e.g. substrates subsequently removed by etching
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
- C23C16/301—AIII BV compounds, where A is Al, Ga, In or Tl and B is N, P, As, Sb or Bi
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- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
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Abstract
The invention relates to a substrate stripping method based on a laminated mask substrate. The method comprises the following steps: 1) growing a III-nitride material on the three-dimensional laminated mask substrate by using an MOCVD (metal organic chemical vapor deposition) technology to form a III-nitride material film; 2) growing a group III nitride material on the continuous thin film using HVPE techniques to form a group III nitride material thick film; 3) self-separation is achieved by cooling to create stress between the three-dimensional stacked mask substrate and the group III nitride material thick film. By adopting the method, due to the weak connectivity with the substrate, the self-separation can be realized with the substrate in the cooling process, the expensive technologies such as laser stripping and the like are avoided, the process steps and time are saved, the production yield is obviously improved, and the product quality is improved; the adopted special three-dimensional laminated mask substrate can be matched with MOCVD to grow a high-quality thin film, and further a thick film with high crystal quality can be formed by HVPE epitaxy.
Description
Technical Field
The invention belongs to the technical field of semiconductors, and particularly relates to a substrate stripping method based on a laminated mask substrate.
Background
Through research in recent two or three decades, group III nitride materials such as GaN, AlN, InN, AlGaN, and InGaN have been considered as semiconductor materials with very high application value as third-generation semiconductors, since they exhibit many excellent physicochemical properties. HVPE is a commonly used method in the growth technique of free-standing single crystal group III nitride materials because of the difficulty of single crystal growth of group III nitride materials. HVPE is an abbreviation for Hydride Vapor Phase Epitaxy, referring to Hydride Vapor Phase Epitaxy technique. HVPE preparation of group III nitride free-standing thick films faces two major problems: firstly, the warpage of the group III nitride thick film caused by heteroepitaxy is serious; and secondly, separating the epitaxial III-nitride thick film from the substrate. The first problem originates from stress. Due to the large lattice and thermal mismatch between group III nitride materials and the commonly used substrate materials sapphire and silicon, stress builds up with increasing thickness due to lattice mismatch during growth and further stress builds up due to the different thermal expansion coefficient from the substrate material during cooling. Therefore, for thick film III-nitride, the stress is too large, which may cause severe warpage and even crack of the whole film, and significantly reduce the HVPE production yield in industrial production. For the mass production of group III nitride free-standing thick films by HVPE techniques, the first problem to be solved is the problem of warpage. The second problem is the problem of the group III nitride material peeling from the substrate. Since the group III nitride is tightly bonded to the substrate and is very difficult to be stripped, various stripping methods, such as laser stripping, have been developed.
In particular, the prior art mainly has the following disadvantages, taking GaN as an example:
(1) the existing methods for growing self-supporting GaN single crystals mainly comprise an ammonothermal method, a sodium-sulfur method and an HVPE method. The growth rates of the ammonia heat method and the sodium sulfur method are slow, so that the production cost is high, a high-pressure environment is required, and the equipment risk coefficient is large. The HVPE method has a fast growth rate, but the yield is low and is less than 20%. Most of which crumble during cooling. Even if it is not broken, the peeling from the substrate is very difficult. After stripping, the GaN film is warped due to excessive stress during growth on the substrate, crystal lattices are twisted, and after the GaN film is polished flat by a CMP process, the crystal orientation of the surface is inconsistent, so that a plurality of subsequent problems exist when the GaN film is used as the substrate.
(2) In other technical schemes which achieve easy separation through a porous structure or nanowire bedding and the like, because GaN does not grow on a regular lattice-matched substrate, the growth quality of an early MOCVD layer is not high. Therefore, the HVPE technology is used for extending and thickening the film, the defect density is reduced, but the reduction degree is limited, so that the overall crystal quality of the finally grown thick film product is not high, and the use value is not high.
(3) The technology for growing the first layer of GaN film by using the patterned substrate or the common lateral epitaxy technology has the advantages that the common patterned substrate or the common lateral epitaxy technology has a large amount of concentrated dislocation generation in a window area, so that the overall crystal quality is improved, but the improvement degree is limited. And because the wing area of the common lateral epitaxy tilts, a large number of defects including dislocation, holes and the like are generated in the folding area, the integral quality is seriously influenced, and the crystal quality in a local area is improved. These high density defect regions can degrade device performance when the device is epitaxial and thus such techniques still do not fully meet industry needs.
Disclosure of Invention
The invention aims to solve the problems that a group III nitride thick film grown by HVPE technology is fragile and difficult to be stripped from a substrate.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a substrate stripping method based on a laminated mask substrate comprises the following steps:
1) growing a III-nitride material on the three-dimensional laminated mask substrate by using an MOCVD (metal organic chemical vapor deposition) technology to form a III-nitride material film;
2) growing a group III nitride material on the continuous thin film using HVPE techniques to form a group III nitride material thick film;
3) self-separation is achieved by cooling to create stress between the three-dimensional stacked mask substrate and the group III nitride material thick film.
Further, the thickness of the group III nitride material film in the step 1) is 1-20 microns.
Further, the thickness of the group III nitride material thick film in the step 2) is 20-500 microns.
Further, for the III-nitride material thick film after self-separation, a self-supporting stress-free single crystal wafer is obtained through a surface planarization process.
Further, the three-dimensional laminated mask substrate in the step 1) comprises a substrate, wherein a bottom layer mask layer and a top layer mask layer are sequentially arranged on the substrate; the bottom mask layer is provided with periodically distributed windows, and the symmetry of the pattern of the windows in a plane is consistent with the crystal symmetry of the hexagonal III-nitride material or is a subset of the crystal symmetry; the top layer mask layer and the bottom layer mask layer have the same pattern of windows, and the positions of the windows are staggered; the top mask layer is connected with the bottom mask layer through a dielectric layer.
Further, the graphic of the window is one of the following: strip shape, regular triangle shape and regular hexagon shape.
Further, the top and bottom mask layers are SiNxThe dielectric layer is SiO2。
Further, step 1) comprises:
a) in the low-temperature nucleation stage, III-group nitride nucleation points are formed on the surface of the substrate exposed out of the bottom layer mask window, and the III-group nitride starts to form island-shaped structure atomic groups by taking the nucleation points as centers;
b) raising the temperature, growing the III-nitride under the normal III-nitride growth parameter condition, and drilling a channel by the grown III-nitride along with the increase of time to expose a top mask window and form a protruding shape;
c) after a channel is drilled and a certain height is formed outside a top layer window, growth parameters are switched, the transverse growth rate is far higher than the vertical growth rate by adopting the MOCVD lateral epitaxy technology, and the III-nitride film is grown until the III-nitride is folded into a flat large plane, namely the III-nitride film is formed.
Further, step 3) uses laser lift-off technology to assist in achieving substrate lift-off.
Further, the III-nitride material is GaN, AlN, InN or ternary or quaternary alloy formed by the GaN, the AlN and the InN.
Compared with the prior art, the invention has the following two remarkable advantages:
1. due to the weak connectivity with the substrate, the film can be self-separated from the substrate in the cooling process, and the group III nitride thick film and the substrate are prevented from being separated by expensive technologies such as laser lift-off and the like. The effect of separating the III-group nitride thick film from the substrate can be achieved without the steps of laser stripping and the like, so that the process steps and time are saved, the production yield is greatly improved, crystal distortion does not exist, and the warped crystal is not required to be ground by using a grinding process; not only effectively reduces the comprehensive cost, but also improves the product quality. This is a key point for large-scale application of group III nitride high quality homogeneous substrates.
2. As the adopted special three-dimensional laminated mask substrate can be matched with MOCVD to grow a high-quality thin film, as a preorder process step of HVPE, a thick film with high crystal quality can be obtained by HVPE epitaxy. Taking GaN material growth as an example, the invention can prepare the dislocation density of 10 at lower cost5/cm2The self-supporting GaN substrate is obviously superior to other existing methods.
Drawings
FIG. 1 is a schematic diagram of stress distortion of a planar substrate grown III-nitride free-standing thick film, wherein (a) is a compressive stress distortion and (b) is a tensile stress distortion.
Fig. 2 is a schematic diagram of the self-segregation principle of growing thick film group III nitride using a tailored three-dimensional stacked mask substrate of the present invention.
Fig. 3 is a graph showing the effect of self-detachment of a 20 μm thick GaN film from a tailored stacked mask substrate during a temperature reduction process under a microscope.
Fig. 4 is a schematic three-dimensional structure of a strip-shaped substrate, in which: 1-top mask layer, 2-substrate, 3-top window, 4-bottom window, 5-bottom mask layer, 6-dielectric layer connecting top mask layer and bottom mask layer.
Fig. 5 is a graph having the same symmetry as the gallium nitride crystal structure, in which the graph (a), the graph (b), and the graph (c) are in the order of a stripe, a triangle, and a hexagon.
FIG. 6 is a schematic plan view of a substrate design in the form of a stripe, triangle, or hexagon pattern, wherein the (a), (b), (c) sequentially represent stripe, triangle, and hexagon windows, the dotted line represents the lower window, and the solid line represents the upper window.
FIG. 7 is a scanning electron microscope image of gallium nitride growth on a substrate with different patterns, wherein (a), (b) and (c) show the scanning electron microscope images of gallium nitride growth on a substrate with triangular, hexagonal and bar patterns in sequence. The figure shows an intermediate state of growth, continued growth will form a closed film.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, the present invention shall be described in further detail with reference to the following detailed description and accompanying drawings.
The invention aims to solve the problems that a group III nitride thick film grown by HVPE technology is fragile and difficult to be stripped from a substrate. By using the substrate and the growth process provided by the invention, the complete III-nitride thick film and the substrate can be separated from each other, the production yield is improved, and the high-quality self-supporting single crystal III-nitride thick film is obtained. Because the high-quality self-supporting III-group nitride single crystal substrate and the epitaxial growth III-group nitride layer to be used for device preparation have no lattice mismatch and thermal mismatch, the crystal quality of the epitaxial layer is greatly improved, so that the performance of the device is closer to the theoretical limit of materials, the performance is improved, the service life of the device is prolonged, and the self-supporting III-group nitride single crystal substrate is the best choice for epitaxially growing high-quality devices. However, it is difficult to prepare a high quality free-standing group III nitride single crystal substrate, mainly with low yield, high cost and long time consumption. The invention aims to improve the preparation yield of the III-nitride self-supporting thick film, reduce the cost, improve the crystal quality and the process stability and provide raw material supply for the III-nitride related industries.
As shown in fig. 1, when a group III nitride thick film is grown by a conventional method, the substrate and the thin film may warp due to excessive stress, and during cooling, the thermal stress further aggravates the warp, so that the thin film may crack or even crack. Even if the thick film material is stripped by the laser stripping technology, the thick film material still needs to be subjected to a grinding process, and the ground surface is only the surface, so that the problem of lattice distortion still exists, and the thick film quality is not high. Obtaining a complete large sheet of high quality, free-standing group III nitride thick films is difficult due to low yield.
In the invention, a specially-made three-dimensional laminated mask substrate is used, the growth method is divided into two steps, firstly, MOCVD equipment/technology is used for growing the III-group nitride material on the mask substrate to form a high-quality continuous film with the thickness of 1-20 microns, and on the basis, the HVPE technology is used for growing the III-group nitride, and the advantage of high growth rate is used for accelerating the growth rate of the III-group nitride film to grow the III-group nitride thick film with the thickness of 20-500 microns. MOCVD can grow higher quality group III nitrides directly on substrates such as sapphire or silicon, but at slower growth rates. HVPE has difficulty in growing high-quality group III nitride single crystals directly on substrates such as sapphire and silicon, but can grow high-quality single crystals on group III nitride layers, and the growth rate is high. Thus, the group III nitride thick film growth step is generally divided into two steps, which enables high quality crystals to be obtained. Due to the special structure of the mask substrate, no chemical bond is formed between the mask layer and the group III nitride film, and the mask layer and the group III nitride film are combined by weak van der Waals force, so that the direct connection part of the group III nitride film and the substrate is few and can be broken under huge stress. In the growth process, the temperature of the growth condition is higher, so that the thermal stress between the substrate and the thick film cannot be reflected, and in the cooling process, the large stress can be generated due to the large difference of the thermal expansion coefficients between the substrate and the group III nitride thick film, so that the weakest channel is twisted off and connected, and the self-separation effect is achieved, as shown in fig. 2.
After the self-separated thick film III-nitride is subjected to a surface planarization process, a self-supporting stress-free single crystal wafer can be obtained, and the self-supporting stress-free single crystal wafer can be used for various researches and device production of III-nitride related industries.
The experimental case of fig. 3 shows a self-separation effect, but since the film thickness is not thick enough, it cannot exist self-supporting after self-separation, and is easily broken. The self-separated film can keep the integrity thereof only by optimizing growth conditions to flatten the surface and thickening the film by using the HVPE technology.
The key point of the present invention is the use of a tailored three-dimensional stacked mask substrate to grow a thick film of group III nitride that can be self-separated. The use of a specially-made three-dimensional laminated mask substrate is the most critical point because the substrate can weaken the direct connection strength between the film and the substrate to achieve the effect of easy stripping, and also can keep very high crystal quality when the initial film layer is grown by MOCVD (metal organic chemical vapor deposition), so that the overall crystal quality of the film which is epitaxially thickened by using the HVPE method is very high, and the dislocation density can be lower than 105/cm2。
FIG. 4 is a schematic diagram of a tailored three-dimensional laminated mask substrate structure of the present invention. The top mask layer 1 and the bottom mask layer 5 on the substrate 2 are both provided with periodically distributed strip-shaped windows, namely, the top window 3 and the bottom window 4, but are staggered with each other. The top mask layer 1 and the bottom mask layer 5 are connected through a dielectric layer 6. The material of the top mask layer 1 and the bottom mask layer 5 may be SiNxEtc., the material of the dielectric layer 6 may be SiO2And the like.
The bottom mask layer is provided with special pattern windows distributed periodically, and can be regular triangles and regular hexagons besides the stripes in fig. 4, as shown in fig. 5. The patterns are the patterns with the in-plane symmetry consistent with the crystal symmetry of the III-group nitride materials such as GaN and the like or subsets of the patterns, and the patterns with the special symmetry can be used for preparing the continuous and flat high-quality III-group nitride films such as epitaxial layer GaN and the like which are paved on the whole substrate surface and can be more fully compatible with the subsequent device process. The top and bottom mask layers are patterned identically but offset from each other as shown in fig. 6, where the dashed lines represent the lower level windows and the solid lines represent the upper level windows.
The growth of group III nitrides on the 3D stacked mask substrate structure of the present invention is as follows:
1) initially, a low temperature nucleation stage is required through which group III nitride nucleation sites are formed on the substrate surface exposed by the underlying mask window. Centered on these points, the group III nitride starts to form island-like structural radicals.
2) The temperature is then raised and the growth of the group III nitride is performed under normal group III nitride growth parameters, and over time the grown group III nitride will drill out the trench, exposing the top mask window, forming the protruding shape.
3) After the channel is drilled and a certain height is formed outside the top window, the growth parameters are switched, and the lateral epitaxy technique (such as the MOCVD lateral epitaxy technique described earlier in the present invention) is adopted, so that the lateral growth rate is far greater than the vertical growth rate. The growth is continued until the III-nitride is folded into a flat large plane, and the III-nitride film is formed.
FIG. 7 is a scanning electron micrograph of gallium nitride grown on a substrate of different patterns, shown as an intermediate state of growth, continuing to grow to form a closed film.
In addition to being easy to crack, the traditional method for growing the group III nitride thick film on the planar substrate also needs a laser lift-off technology to separate the group III nitride thick film from the substrate. The technical difficulty of laser lift-off is also very high, which brings about further reduction of yield and longer time consumption for the process, thus the cost is higher. The method has the advantages that the effect of separating the III-group nitride thick film from the substrate can be achieved without a laser stripping step, so that the process steps and time are saved, the production yield is greatly improved, the yield of the stripped thick film is expected to exceed 90%, and no crystal distortion exists. Not only greatly reduces the comprehensive cost, but also improves the product quality, which is a key point for the large-scale application of the III-nitride high-quality homogeneous substrate. Once high quality homogeneous III-nitride substrates are applied in large scale, many of the long standing industry problems will be solved and the performance of the devices produced will be greatly improved. In the field of power electronic devices, the voltage withstanding value of the device can be improved, and the heat loss of the device can be reduced. In the field of radio frequency devices, the power density and the radio frequency conversion efficiency can be improved, the working voltage is reduced, and the frequency application range is enlarged. In the field of photoelectric devices, the LED can be used as a device with a vertical structure, so that the luminous efficiency is greatly improved, and the complexity of a driving circuit is reduced.
Some current techniques can produce a self-peeling effect. For example, the nanowire is paved on a planar substrate, so that the connection strength of the grown III-nitride film and the substrate is weakened, and the effect of easy stripping is achieved. There are also methods to weaken the bonding strength of the substrate to the membrane by first preparing a porous group III nitride on a planar substrate. In addition, the method uses a common pattern substrate for growth, and also aims to weaken the connection strength of the substrate and the gallium nitride film and achieve the effect of easy peeling. However, these methods are not as high quality thick film crystals that are eventually epitaxial by HVPE because some of the group III nitride films prior to using HVPE techniques are not as high quality. Taking GaN material growth as an example, a common pattern substrate can enable the total dislocation density to be close to 106/cm2However, due to the non-uniformity, the defect density is still very high in the concentrated area. By the technique of the invention, dislocation density lower than 10 can be prepared5/cm2The self-supporting GaN substrate is obviously superior to other existing methods.
The above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person skilled in the art can modify the technical solution of the present invention or substitute the same without departing from the principle and scope of the present invention, and the scope of the present invention should be determined by the claims.
Claims (10)
1. A substrate stripping method based on a laminated mask substrate is characterized by comprising the following steps:
1) growing a III-nitride material on the three-dimensional laminated mask substrate by using an MOCVD (metal organic chemical vapor deposition) technology to form a III-nitride material film;
2) growing a group III nitride material on the continuous thin film using HVPE techniques to form a group III nitride material thick film;
3) self-separation is achieved by cooling to create stress between the three-dimensional stacked mask substrate and the group III nitride material thick film.
2. The method according to claim 1, wherein the thickness of the group III nitride material thin film in the step 1) is 1 to 20 μm.
3. The method of claim 1, wherein the group III nitride material thick film of step 2) has a thickness of 20 to 500 μm.
4. The method of claim 1, wherein for the self-separated group III-nitride material thick film, a self-supporting stress-free single crystal wafer is obtained through a surface planarization process.
5. The method according to claim 1, wherein the three-dimensional laminated mask substrate of step 1) comprises a substrate on which a bottom mask layer and a top mask layer are sequentially disposed; the bottom mask layer is provided with periodically distributed windows, and the symmetry of the pattern of the windows in a plane is consistent with the crystal symmetry of the hexagonal III-nitride material or is a subset of the crystal symmetry; the top layer mask layer and the bottom layer mask layer have the same pattern of windows, and the positions of the windows are staggered; the top mask layer is connected with the bottom mask layer through a dielectric layer.
6. The method of claim 5, wherein the graphic of the window is one of: strip shape, regular triangle shape and regular hexagon shape.
7. Method according to claim 5 or 6, characterized in that the top and bottom mask layers are SiNxThe dielectric layer is SiO2。
8. The method according to claim 5 or 6, wherein step 1) comprises:
a) in the low-temperature nucleation stage, III-group nitride nucleation points are formed on the surface of the substrate exposed out of the bottom layer mask window, and the III-group nitride starts to form island-shaped structure atomic groups by taking the nucleation points as centers;
b) raising the temperature, growing the III-nitride under the normal III-nitride growth parameter condition, and drilling a channel by the grown III-nitride along with the increase of time to expose a top mask window and form a protruding shape;
c) after a channel is drilled and a certain height is formed outside a top layer window, growth parameters are switched, the transverse growth rate is far higher than the vertical growth rate by adopting the MOCVD lateral epitaxy technology, and the III-nitride film is grown until the III-nitride is folded into a flat large plane, namely the III-nitride film is formed.
9. The method of claim 1, wherein step 3) uses a laser lift-off technique to assist in effecting substrate lift-off.
10. The method of claim 1, wherein the ill-nitride material is GaN, AlN, InN, or a ternary or quaternary alloy thereof.
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