Gallium nitride epitaxial structure and preparation method thereof

Abstract

The invention discloses a gallium nitride epitaxial structure and a preparation method, the gallium nitride epitaxial structure comprises a substrate layer, a nucleating layer, a stress adjusting layer and an epitaxial layer which are stacked in sequence along a first direction, and the nucleating layer and the stress adjusting layer both comprise a first element; the stress adjusting layer comprises a plurality of stress slow-release layers stacked in the first direction, and at least one stress slow-release layer comprises a plurality of stress slow-release sub-layers stacked in the first direction; in the plurality of stress slow-release layers, the molar content of the first element of the stress slow-release layer closer to the nucleating layer is greater than the molar content of the first element of the stress slow-release layer farther from the nucleating layer; in the same stress slow-release layer, the molar content of the first element of at least one stress slow-release sub-layer is smaller than the molar content of the first element of the stress slow-release sub-layer farther away from the nucleating layer. According to the invention, the problem that cracks are easy to generate during preparation of the gallium nitride material can be improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a gallium nitride epitaxial structure and its fabrication method. Background Technology

[0002] In the field of semiconductor materials, due to the inherent properties of the materials, it is difficult for traditional silicon-based devices to achieve revolutionary breakthroughs in performance. In recent years, however, gallium nitride (GaN) materials, with their advantages such as large bandgap, strong breakdown electric field, high electron mobility, high conversion efficiency, high thermal conductivity, and low loss, have gradually replaced silicon-based devices in certain applications within the semiconductor field. These applications include widespread use in communications, radar, consumer electronics, automotive electronics, power energy, industrial laser processing, and instrumentation. Therefore, the development and mass production of gallium nitride materials and devices have attracted significant attention from many countries worldwide. However, the current preparation of gallium nitride materials suffers from a tendency to develop cracks. Summary of the Invention

[0003] This application provides a gallium nitride epitaxial structure and its preparation method to improve the problem of easy cracking in the preparation of gallium nitride materials.

[0004] According to one aspect of this application, a gallium nitride epitaxial structure is provided, comprising a substrate layer, a nucleation layer, a stress-regulating layer, and an epitaxial layer. The nucleation layer is disposed on one side of the substrate layer along a first direction; the stress-regulating layer is disposed on the side of the nucleation layer opposite to the substrate layer; and the epitaxial layer is disposed on the side of the stress-regulating layer opposite to the substrate layer. Both the nucleation layer and the stress-regulating layer include a first element. The stress-regulating layer includes a plurality of stress-relieving layers stacked along the first direction, wherein at least one stress-relieving layer includes a plurality of stress-relieving sub-layers stacked along the first direction. Among the plurality of stress-relieving layers, the molar content of the first element in the stress-relieving layer closer to the nucleation layer is greater than the molar content of the first element in the stress-relieving layer farther from the nucleation layer. In the same stress-relieving layer, at least one stress-relieving sub-layer has a molar content of the first element that is less than the molar content of the first element in the stress-relieving sub-layer farther from the nucleation layer.

[0005] In some embodiments, within the same stress-relieving layer, the molar content of the first element in the stress-relieving sublayer closer to the nucleation layer is less than the molar content of the first element in the stress-relieving sublayer farther from the nucleation layer.

[0006] In some embodiments, each of the stress relief layers includes a plurality of the stress relief sublayers.

[0007] In some embodiments, the plurality of stress-relieving layers include a first stress-relieving layer and a second stress-relieving layer disposed on the side of the first stress-relieving layer opposite to the nucleation layer; the first stress-relieving layer includes a first stress-relieving sublayer and a second stress-relieving sublayer disposed on the side of the first stress-relieving sublayer opposite to the nucleation layer, the second stress-relieving layer includes a third stress-relieving sublayer and a fourth stress-relieving sublayer disposed on the side of the third stress-relieving sublayer opposite to the nucleation layer; the molar content of a first element in the first stress-relieving sublayer is less than the molar content of a first element in the second stress-relieving sublayer; the molar content of a first element in the third stress-relieving sublayer is less than the molar content of a first element in the fourth stress-relieving sublayer; the molar content of a first element in the first stress-relieving sublayer is greater than the molar content of a first element in the fourth stress-relieving sublayer.

[0008] In some embodiments, the stress conditioning layer further includes a buffer layer located between two adjacent stress relief layers.

[0009] In some embodiments, the buffer layer includes a plurality of buffer sublayers stacked along the first direction; the first element molar content of the buffer sublayer closer to the nucleation layer is greater than the first element molar content of the buffer sublayer further away from the nucleation layer.

[0010] In some embodiments, the epitaxial layer includes a channel layer, an insertion layer, and a barrier layer stacked sequentially along the first direction.

[0011] In some embodiments, the gallium nitride epitaxial structure further includes a high-resistivity breakdown layer disposed between the stress-adjusting layer and the epitaxial layer.

[0012] In some embodiments, the gallium nitride epitaxial structure further includes a cap layer disposed on the side of the epitaxial layer opposite to the substrate layer.

[0013] According to another aspect of this application, a method for preparing a gallium nitride epitaxial structure is provided, comprising the following steps: Provide a substrate layer; A nucleation layer is formed on one side of the substrate layer along the first direction; A stress-regulating layer is formed on the side of the nucleation layer opposite to the substrate layer; An epitaxial layer is formed on the side of the stress-adjusting layer opposite to the substrate layer; Both the nucleation layer and the stress-regulating layer include a first element; The stress conditioning layer includes a plurality of stress relief layers stacked along the first direction, wherein at least one of the stress relief layers includes a plurality of stress relief sub-layers stacked along the first direction. In the plurality of stress relief layers, the molar content of the first element in the stress relief layer closer to the nucleation layer is greater than the molar content of the first element in the stress relief layer farther away from the nucleation layer; In the same stress relief layer, at least one stress relief sublayer has a first element molar content that is less than that of the stress relief sublayer further away from the nucleation layer.

[0014] The gallium nitride epitaxial structure of this application includes a substrate layer, a nucleation layer, a stress-regulating layer, and an epitaxial layer stacked along a first direction. Both the nucleation layer and the stress-regulating layer include a first element. The stress-regulating layer includes multiple stress-relieving layers stacked along the first direction, and at least one stress-relieving layer includes multiple stress-relieving sub-layers stacked along the first direction. Among the multiple stress-relieving layers, the molar content of the first element in the stress-relieving layer closer to the nucleation layer is greater than that in the stress-relieving layer farther from the nucleation layer. That is, along the direction away from the nucleation layer, the molar content of the first element in the multiple stress-relieving layers gradually decreases. Thus, the stress-regulating layer has a high lattice matching degree with the nucleation layer and the epitaxial layer on opposite sides along the first direction, respectively, reducing the stress introduced by the lattice mismatch between the nucleation layer and the epitaxial layer.

[0015] Furthermore, among the multiple stress-relieving sublayers of the same stress-relieving layer, at least one stress-relieving sublayer has a lower first element molar content than the stress-relieving sublayer further away from the nucleation layer. That is, the first element molar content gradient of at least some of the stacked structures in the same stress-relieving layer is opposite to the first element molar content gradient of the stacked structure formed by multiple stress-relieving layers, which improves the deformability of the entire epitaxial structure and thus inhibits the generation and propagation of cracks. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of a gallium nitride epitaxial structure in one embodiment of this application is shown.

[0018] Figure 2 The results of wafer surface defect detection are shown in some embodiments and comparative examples of this application.

[0019] Explanation of reference numerals in the attached figures: 1. Gallium nitride epitaxial structure; 10. Substrate layer; 20. Nucleation layer; 30. Stress-regulating layer; 31. First stress-relieving layer; 311. First stress-relieving sublayer; 312. Second stress-relieving sublayer; 32. Second stress-relieving layer; 321. Third stress-relieving sublayer; 322. Fourth stress-relieving sublayer; 33. Buffer layer; 40. High-resistance pressure-resistant layer; 50. Epitaxial layer; 51. Channel layer; 52. Insertion layer; 53. Barrier layer; 60. Cap layer; X, the first direction. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0021] In the following description, when referring to the accompanying drawings, the same numbers in different drawings denote the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0022] Gallium nitride (GaN) is a non-naturally occurring material, and its inherent physicochemical properties make it difficult to process. The main methods used in the industry to prepare GaN materials include single-crystal growth or epitaxy. Due to the difficulty, high cost, and low production capacity of single-crystal growth, a revolutionary breakthrough in GaN single-crystal preparation technology is unlikely in the short term. Therefore, heterojunction GaN epitaxy has always been the primary source for GaN material and device fabrication. With recent breakthroughs in the technological capabilities and stability of heterojunction GaN epitaxy, the production capacity and cost of GaN devices have gradually become the main competitive factors in the industry. Furthermore, the idle or obsolete production lines resulting from the development of large-size silicon industries have provided readily available processing platforms for GaN, further driving the shift in GaN epitaxial manufacturing from 6-inch to 8-inch wafers.

[0023] Unlike homoepitaxial growth using silicon (Si) and silicon carbide (SiC), gallium nitride (GaN) heteroepitaxial growth often uses silicon as a substrate. The significant differences in crystal structure and physical properties between GaN and silicon result in GaN experiencing substantial stress during epitaxial growth. Furthermore, GaN's inherent brittleness leads to poor deformation capacity, making it prone to edge cracking. At the same curvature level, the increasing size of GaN epitaxy undoubtedly exacerbates the edge stress problem, amplifying the issue of edge cracking in epitaxial wafers.

[0024] The presence and propagation of cracks often lead to a significant reduction in the usable area of ​​the wafer, while also increasing the risk of fragmentation during wafer processing, resulting in decreased throughput, increased costs, and reduced production capacity, thus deviating from the original intention of increasing wafer size. Therefore, how to reduce the crack problem caused by edge stress under the condition of large size is an important issue for the industry to improve the yield of gallium nitride epitaxy and devices, reduce costs, and enhance core competitiveness.

[0025] To address the cracking problem in large-size gallium nitride epitaxial wafers, although some or all of the aluminum gallium nitride buffer layer structure is replaced by a superlattice in related technologies, which can improve the crack level to some extent, the improvement effect is still limited, and there are still problems of local long cracks and overall long cracks.

[0026] To address the aforementioned issues, this application provides a gallium nitride epitaxial structure that breaks with the conventional approach of transitioning the buffer layer from high composition to low resistivity. Instead, it introduces a stress-relieving layer with a reverse composition gradient, which significantly enhances the deformability of the entire epitaxial structure, thereby suppressing the generation and propagation of cracks and greatly improving the edge cracks of large-size silicon-based gallium nitride epitaxial wafers.

[0027] See Figure 1 In some embodiments, the gallium nitride epitaxial structure 1 includes a substrate layer 10, a nucleation layer 20, a stress-adjusting layer 30, and an epitaxial layer 50 stacked along a first direction X. The substrate layer 10 is, for example, a 6-inch or 8-inch polished single-crystal silicon wafer. The nucleation layer 20 is disposed on one side of the substrate layer 10 along the first direction X. The material of the nucleation layer 20 is, for example, aluminum nitride (AlN), and the thickness of the nucleation layer 20 is 100 nm to 350 nm, for example, 110 nm, 150 nm, 200 nm, or 300 nm. The stress-adjusting layer 30 is disposed on the side of the nucleation layer 20 opposite to the substrate layer 10, and the stress-adjusting layer 30 includes, for example, at least one of aluminum gallium nitride (AlGaN) and aluminum nitride (AlN). The epitaxial layer 50 is a working layer and is disposed on the side of the stress-adjusting layer 30 opposite to the substrate layer 10. Both the nucleation layer 20 and the stress-adjusting layer 30 include a first element. For example, when the nucleation layer 20 is made of aluminum nitride and the stress adjustment layer 30 includes aluminum gallium nitride, the first element is aluminum.

[0028] The stress-regulating layer 30 includes a plurality of stress-relieving layers stacked along a first direction X, wherein at least one stress-relieving layer includes a plurality of stress-relieving sub-layers stacked along the first direction X, that is, a portion of the plurality of stress-relieving layers includes a plurality of stress-relieving sub-layers stacked along the first direction X, or each of the plurality of stress-relieving layers includes a plurality of stress-relieving sub-layers stacked along the first direction X.

[0029] In the multiple stress-relieving layers, the molar content of the first element in the stress-relieving layer closer to the nucleation layer 20 is greater than that in the stress-relieving layer farther away from the nucleation layer 20. Along the direction away from the nucleation layer 20, the molar content of the first element in the multiple stress-relieving layers decreases, for example, uniformly or non-uniformly. In other words, along the direction away from the nucleation layer 20, the molar content of the first element in the multiple stress-relieving layers gradually decreases. Thus, the stress-adjusting layer 30 has a high lattice matching degree with the nucleation layer 20 and the epitaxial layer 50 on opposite sides along the first direction X, reducing the stress introduced by the lattice mismatch between the nucleation layer 20 and the epitaxial layer 50.

[0030] Furthermore, within the same stress-relieving layer, the molar content of the first element in at least one stress-relieving sublayer is less than the molar content of the first element in stress-relieving sublayers further away from the nucleation layer 20. That is, the molar content gradient of the first element in at least a portion of the stacked structure within the same stress-relieving layer is opposite to the molar content gradient of the first element in the stacked structure formed by multiple stress-relieving layers.

[0031] It is understandable that during the epitaxial growth of the thin film in the direction away from the nucleation layer 20, the interatomic spacing gradually changes due to the decreasing molar content of the first element. This may cause the grown layer structure to deform by protruding in the direction away from the nucleation layer 20 or by deforming in the direction towards the nucleation layer 20. Based on this, this embodiment sets a reverse composition gradient within the same stress relief layer, breaking the original gradual change in interatomic spacing. That is, a thin film with a different composition gradient is inserted into the stress relief layer with decreasing molar content of the first element. For example, a thin film with a larger interatomic spacing is inserted between two thin films with smaller interatomic spacing, thereby buffering the stress generated by the unevenness during growth, improving the deformability of the entire epitaxial structure, and thus suppressing the generation and propagation of cracks.

[0032] In some embodiments, in the same stress relief layer, the molar content of the first element in the stress relief sublayer closer to the nucleation layer 20 is less than the molar content of the first element in the stress relief sublayer farther away from the nucleation layer 20. That is, in the same stress relief layer, the molar content of the first element in multiple stress relief sublayers decreases in the direction away from the nucleation layer 20, thereby forming a more uniform reverse composition gradient and further improving the deformability.

[0033] In some embodiments, each stress-relieving layer includes multiple stress-relieving sublayers. This further enhances the uniformity of the forward component gradient and the uniformity of the reverse component gradient.

[0034] In some embodiments, the plurality of stress relief layers include a first stress relief layer 31 and a second stress relief layer 32, wherein the second stress relief layer 32 is disposed on the side of the first stress relief layer 31 facing away from the nucleation layer 20. The thickness of the first stress relief layer 31 may be the same as or different from the thickness of the second stress relief layer 32, and the material of the first stress relief layer 31 may be the same as or different from the material of the second stress relief layer 32. The material of the first stress relief layer 31 is, for example, aluminum gallium nitride, and the material of the second stress relief layer 32 is, for example, aluminum gallium nitride. The thickness of the first stress relief layer 31 is 40 nm to 150 nm, for example, 50 nm, 60 nm, 100 nm, or 120 nm. The thickness of the second stress relief layer 32 is 40 nm to 150 nm, for example, 50 nm, 60 nm, 100 nm, or 120 nm.

[0035] The first stress-relieving layer 31 includes multiple stress-relieving sublayers, and the second stress-relieving layer 32 includes multiple stress-relieving sublayers. The number of stress-relieving sublayers in the first stress-relieving layer 31 is the same as or different from the number of stress-relieving sublayers in the second stress-relieving layer 32. The thicknesses of the multiple stress-relieving sublayers are the same or different. For example, the first stress-relieving layer 31 includes a first stress-relieving sublayer 311 and a second stress-relieving sublayer 312, with the second stress-relieving sublayer 312 disposed on the side of the first stress-relieving sublayer 311 facing away from the nucleation layer 20. The second stress-relieving layer 32 includes a third stress-relieving sublayer 321 and a fourth stress-relieving sublayer 322, with the fourth stress-relieving sublayer 322 disposed on the side of the third stress-relieving sublayer 321 facing away from the nucleation layer 20.

[0036] The molar content of the first element in the first stress-relieving sublayer 311 is less than that in the second stress-relieving sublayer 312, and the molar content of the first element in the third stress-relieving sublayer 321 is less than that in the fourth stress-relieving sublayer 322. The molar content of the first element in the first stress-relieving sublayer 311 is greater than that in the fourth stress-relieving sublayer 322. Based on this, the molar content of the first element in the multiple stress-relieving sublayers within the first stress-relieving layer 31 increases in the direction away from the nucleation layer 20, and the molar content of the first element in the multiple stress-relieving sublayers within the second stress-relieving layer 32 also increases in the direction away from the nucleation layer 20. The molar content of the first element in the first stress-relieving layer 31 is greater than that in the second stress-relieving layer 32. This reduces the stress introduced by the lattice mismatch between the nucleation layer 20 and the epitaxial layer 50, and further reduces the stress introduced by the compositional gradient change in the stress-adjusting layer 30.

[0037] Optionally, the first stress-relieving sublayer 311 and the second stress-relieving sublayer 312 are aluminum gallium nitride (AllaGa(1-a)N) and AlbGa(1-b)N with different aluminum molar contents, respectively, and 0.5 ≤ a < b ≤ 1. The thickness of the first stress-relieving sublayer 311 is 20 nm to 80 nm, for example, 25 nm, 30 nm, 50 nm or 70 nm. The thickness of the second stress-relieving sublayer 312 is 20 nm to 80 nm, for example, 25 nm, 30 nm, 50 nm or 70 nm. The third stress-relieving sublayer 321 and the fourth stress-relieving sublayer 322 are aluminum gallium nitride (AlcGa(1-c)N) and AldGa(1-d)N with different aluminum molar contents, respectively, and 0 ≤ c < d ≤ 0.5. The thickness of the third stress-relieving sublayer 321 is 20 nm to 80 nm, for example, 25 nm, 30 nm, 50 nm or 70 nm. The thickness of the fourth stress-relieving sublayer 322 is 20nm~80nm, for example, 25nm, 30nm, 50nm or 70nm. It is understandable that if the thickness of the stress-relieving layer is too small, it may not provide adequate buffering; if the thickness is too large, it occupies too much thickness space, resulting in less actual gallium nitride material grown, which may affect its electrical properties. This embodiment designs an appropriate thickness, which both alleviates stress and ensures good electrical performance of the gallium nitride epitaxial structure 1.

[0038] In some embodiments, the stress-adjusting layer 30 further includes a buffer layer 33 located between two adjacent stress-relieving layers. The structure of the buffer layer 33 is, for example, a multilayer aluminum gallium nitride structure or a multilayer superlattice structure. The thickness of the buffer layer 33 is 500 nm to 3000 nm, for example, 600 nm, 700 nm, 1000 nm or 2000 nm.

[0039] Optionally, the buffer layer 33 includes a plurality of buffer sublayers stacked along the first direction X, wherein the first element molar content of the buffer sublayer closer to the nucleation layer 20 is greater than the first element molar content of the buffer sublayer further away from the nucleation layer 20.

[0040] Optionally, the buffer layer 33 can be an x-layer aluminum gallium nitride structure, where x ≥ 2. The aluminum content of the buffer layer 33 decreases sequentially along the direction away from the nucleation layer 20, satisfying AlGaN1 > AlGaN2 > ... > AlGaNx.

[0041] Optionally, the buffer layer 33 can be a y-layer superlattice structure, where y ≥ 2, and the superlattice structure is at least one of AlN / AlGaN, AlGaN / AlGaN, and AlGaN / GaN. The effective aluminum content of the superlattice decreases sequentially along the direction away from the nucleation layer 20, satisfying SL1>SL2>…>SLy.

[0042] Based on this, the gallium nitride epitaxial structure 1 in this embodiment employs two sets of stress buffer layers 33, located at the upper and lower ends of the buffer layer 33 respectively. This ensures that the buffer layer 33 filters defects while maximally alleviating the enormous stress caused by the nucleation layer 20 and the buffer layer 33, without affecting the electrical performance of the epitaxial layer 50 and other structures. Furthermore, if the thickness of the stress relief layer is too small, it may not provide a buffering effect; if the thickness of the stress relief layer is too large, it occupies too much thickness space, resulting in less actual gallium nitride material grown, which may affect its electrical performance. This embodiment designs an appropriate thickness, which both alleviates stress and ensures good electrical performance of the gallium nitride epitaxial structure 1.

[0043] In some embodiments, the epitaxial layer 50 includes a channel layer 51, an insertion layer 52, and a barrier layer 53 sequentially stacked along a first direction X. The channel layer 51 is made of, for example, intrinsic gallium nitride, the insertion layer 52 is made of, for example, aluminum nitride, and the barrier layer 53 is made of, for example, aluminum gallium nitride. The thickness of the channel layer 51 is 150 nm to 350 nm, for example, 200 nm, 250 nm, 300 nm, or 310 nm. The thickness of the insertion layer 52 is 0.5 nm to 1.5 nm, for example, 0.6 nm, 0.7 nm, 1 nm, or 1.2 nm. The thickness of the barrier layer 53 is 10 nm to 25 nm, for example, 11 nm, 12 nm, 15 nm, or 20 nm. The channel layer 51, the insertion layer 52, and the barrier layer 53 constitute the working layer, realizing the corresponding functions.

[0044] In some embodiments, the gallium nitride epitaxial structure 1 further includes a high-resistivity voltage withstand layer 40, which is disposed between the stress-adjusting layer 30 and the epitaxial layer 50. The material of the high-resistivity voltage withstand layer 40 is, for example, gallium carbon-doped carbon nitride, and the doping source is at least one selected from ethylene, acetylene, propane, and butane. The thickness of the high-resistivity voltage withstand layer is 800 nm to 1800 nm, for example, 900 nm, 1000 nm, 1200 nm, or 1500 nm. Thus, the voltage withstand strength can be improved through the high-resistivity voltage withstand layer 40.

[0045] In some embodiments, the gallium nitride epitaxial structure 1 further includes a cap layer 60, which is disposed on the side of the epitaxial layer 50 facing away from the substrate layer 10. The material of the cap layer 60 is, for example, one of intrinsic gallium nitride, silicon nitride, or p-type gallium nitride. The thickness of the cap layer 60 is 1 nm to 90 nm, for example, 10 nm, 20 nm, 30 nm, or 50 nm. In this way, the cap layer 60 can provide protection.

[0046] Based on the same inventive concept, this application also provides a method for fabricating a gallium nitride epitaxial structure, comprising the following steps: Substrate layer 10 is provided; A nucleation layer 20 is formed on one side of the substrate layer 10 along the first direction X; A stress-regulating layer 30 is formed on the side of the nucleation layer 20 that is away from the substrate layer 10; An epitaxial layer 50 is formed on the side of the stress-adjusting layer 30 that is away from the substrate layer 10; Both the nucleation layer 20 and the stress-regulating layer 30 include the first element; The stress conditioning layer 30 includes a plurality of stress relief layers stacked along a first direction X, wherein at least one stress relief layer includes a plurality of stress relief sublayers stacked along the first direction X. Among the multiple stress relief layers, the molar content of the first element in the stress relief layer closer to the nucleation layer 20 is greater than that in the stress relief layer farther away from the nucleation layer 20. Within the same stress relief layer, at least one stress relief sublayer has a first element molar content that is less than that of the stress relief sublayer further away from the nucleation layer 20.

[0047] Optionally, forming a stress-regulating layer 30 on the side of the nucleation layer 20 away from the substrate layer 10 includes: forming a first stress-relieving layer 31 on the side of the nucleation layer 20 away from the substrate layer 10; forming a buffer layer 33 on the side of the first stress-relieving layer 31 away from the nucleation layer 20; and forming a second stress-relieving layer 32 on the side of the buffer layer 33 away from the first stress-relieving layer 31.

[0048] Optionally, the method further includes forming a high-resistance pressure-resistant layer 40 on the side of the second stress-relieving layer 32 opposite to the buffer layer 33.

[0049] Optionally, forming an epitaxial layer 50 on the side of the stress-adjusting layer 30 away from the substrate layer 10 includes: forming a channel layer 51 on the side of the high-resistivity withstand voltage layer 40 away from the second stress-relieving layer 32; forming an insertion layer 52 on the side of the channel layer 51 away from the high-resistivity withstand voltage layer 40; and forming a barrier layer 53 on the side of the insertion layer 52 away from the channel layer 51.

[0050] Optionally, the method further includes forming a cap layer 60 on the side of the barrier layer 53 opposite to the insertion layer 52.

[0051] Optionally, the fabrication process of the above-mentioned layered structures is at least one of Metal-Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE).

[0052] Based on this, the method for fabricating the gallium nitride epitaxial structure 1 of this application forms a substrate layer 10, a nucleation layer 20, a first stress relief layer 31, a buffer layer 33, a second stress relief layer 32, a high-resistivity withstand voltage layer 40, a channel layer 51, an insertion layer 52, a barrier layer 53, and a cap layer 60 stacked together. Among them, the first stress relief layer 31 and the second stress relief layer 32 are both composed of two AlGaN structures with different aluminum contents, and the aluminum content of the upper AlGaN is higher than that of the lower layer. This reverse aluminum composition gradient method greatly improves the deformability of the entire epitaxial structure, effectively suppresses the generation of cracks in the epitaxial wafer, and improves the yield, utilization rate, and subsequent processing yield of the epitaxial wafer.

[0053] The following will further illustrate the beneficial effects of the above-described inventive concept based on different embodiments and comparative examples.

[0054] Example 1 In this embodiment, the method for fabricating a gallium nitride epitaxial structure includes the following steps: Step 1: Provide an 8-inch low-resistivity monocrystalline silicon substrate layer; Step 2: An AlN nucleation layer is prepared on the substrate layer from Step 1 using an in-situ MOCVD process. The thickness of the nucleation layer is 200 nm. Step 3: On the nucleation layer of Step 2, the first stress relief layer and the second stress relief layer are sequentially prepared by in-situ MOCVD process to form the first stress relief layer. The material of the first stress relief layer is Al0.65Ga0.35N, and the material of the second stress relief layer is Al0.80Ga0.20N. The thickness of both the first stress relief layer and the second stress relief layer is 50nm. Step four: On the first stress relief layer in step three, four AlGaN structures are sequentially grown using in-situ MOCVD process to form a buffer layer. The materials of the four AlGaN structures are Al0.70Ga0.30N, Al0.50Ga0.50N, Al0.30Ga0.70N, and Al0.20Ga0.80N, respectively, with thicknesses of 300nm, 600nm, 600nm, and 900nm, respectively. Step 5: On the buffer layer of step 4, the third stress relief sublayer and the fourth stress relief sublayer are grown sequentially by in-situ MOCVD process to form the second stress relief layer. The material of the third stress relief sublayer is Al0.05Ga0.95N, and the material of the fourth stress relief sublayer is Al0.15Ga0.85N. The thickness of the third stress relief sublayer and the fourth stress relief sublayer is 50nm. Step 6: On the second stress relief layer in step 5, a high-resistivity withstand voltage layer is grown by in-situ MOCVD process. The material of the high-resistivity withstand voltage layer is carbon-doped GaN, the doping source is ethylene, the doping flow rate is 300 sccm, the doping carbon concentration is 2E19 atom / cm3, and the thickness of the high-resistivity withstand voltage layer is 1500 nm. Step 7: On the high-resistivity withstand voltage layer of step 6, a channel layer is grown in situ using MOCVD process. The material of the channel layer is intrinsic GaN, and the thickness is 300nm. Step 8: An insertion layer is grown on the channel layer in step 7 using an in-situ MOCVD process. The material of the insertion layer is AlN, and the thickness is 1 nm. Step 9: A barrier layer is grown on the insertion layer of Step 8 using an in-situ MOCVD process. The material of the barrier layer is Al0.22Ga0.78N, and the thickness is 15nm. Step 10: A cap layer is grown on the barrier layer of step 9 using an in-situ MOCVD process. The cap layer is made of intrinsic GaN and has a thickness of 2 nm.

[0055] Example 2 The difference between this embodiment and Embodiment 1 lies in step four. Step four in this embodiment includes: In step three, two superlattice structures are sequentially grown on the first stress relief layer using in-situ MOCVD to form a buffer layer. The two superlattice structures are AlN / Al0.50Ga0.50N and Al0.50Ga0.50N / GaN, respectively, with thicknesses of 1000 nm and 1500 nm.

[0056] Comparative Example 1 The difference between this comparative example and Example 1 is that it does not include steps three and five, that is, the first stress relief layer and the second stress relief layer are not formed.

[0057] Comparative Example 2 The difference between this comparative example and Example 2 is that it does not include steps three and five, that is, the first stress relief layer and the second stress relief layer are not formed.

[0058] The wafer surface defects of Examples 1, 2, Comparative Example 1, and Comparative Example 2 were detected using a Candela 8720 surface defect analyzer. The detection results are as follows: Figure 2 As shown in the figure, the dark ring around the edge of Comparative Example 1 and Comparative Example 2 represents the scanned cracks, and the scattered small dots represent the tested particles. The test variable is 2mm.

[0059] As can be seen from the surface defect detection results of Example 1 and Comparative Example 1, compared with Comparative Example 1, the overall crack level of the epitaxial wafer was significantly improved after the introduction of the first stress relief layer and the second stress relief layer in Example 1. Similarly, as can be seen from the surface defect detection results of Example 2 and Comparative Example 2, the crack level of the epitaxial wafer was significantly improved after the introduction of the stress relief layer in the superlattice buffer layer epitaxial structure.

[0060] Specifically, in Comparative Examples 1 and 2, the stress-regulating layer includes a buffer layer but excludes the first and second stress-relieving layers. Along the direction away from the nucleation layer, the Al molar content of the multiple buffer sublayers of the buffer layer decreases progressively. Based on this, although the lattice mismatch between the nucleation layer and the epitaxial layer can be improved, the decreasing Al molar content also leads to a corresponding gradual change in the interatomic spacing, causing significant bulges or depressions in the grown layer structure, generating substantial stress, and making cracks still relatively noticeable.

[0061] In Examples 1 and 2, the stress-regulating layer includes a first stress-relieving layer, a buffer layer, and a second stress-relieving layer. The Al molar content of the first stress-relieving layer, the buffer layer, and the second stress-relieving layer decreases along the direction away from the nucleation layer. Conversely, along the direction away from the nucleation layer, the Al molar content of multiple stress-relieving sublayers of the first stress-relieving layer increases, and the Al molar content of multiple stress-relieving sublayers of the second stress-relieving layer also increases. This decrease in Al molar content across the first stress-relieving layer, the buffer layer, and the second stress-relieving layer improves the lattice mismatch between the nucleation layer and the epitaxial layer. Simultaneously, the reverse gradient of Al molar content in the multiple stress-relieving sublayers within the first stress-relieving layer and the reverse gradient of Al molar content in the multiple stress-relieving sublayers within the second stress-relieving layer buffers the stress caused by uneven deformation during growth, enhancing the deformability of the entire epitaxial structure and thus suppressing crack initiation and propagation.

[0062] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances. Furthermore, in the description of this application, unless otherwise stated, "multiple" means at least two, for example, two, three, four, etc. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship.

[0063] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with the claims of this application shall still fall within the scope of this application.

Claims

1. A gallium nitride epitaxial structure, characterized in that, include: Substrate layer; A nucleation layer is disposed on one side of the substrate layer along the first direction; A stress-regulating layer is disposed on the side of the nucleation layer opposite to the substrate layer; An epitaxial layer is disposed on the side of the stress-adjusting layer opposite to the substrate layer; Both the nucleation layer and the stress-regulating layer include a first element; The stress conditioning layer includes a plurality of stress relief layers stacked along the first direction, wherein at least one of the stress relief layers includes a plurality of stress relief sub-layers stacked along the first direction. In the plurality of stress relief layers, the molar content of the first element in the stress relief layer closer to the nucleation layer is greater than the molar content of the first element in the stress relief layer farther away from the nucleation layer; In the same stress relief layer, at least one stress relief sublayer has a first element molar content that is less than that of the stress relief sublayer further away from the nucleation layer.

2. The gallium nitride epitaxial structure according to claim 1, characterized in that, In the same stress relief layer, the molar content of the first element in the stress relief sublayer closer to the nucleation layer is less than the molar content of the first element in the stress relief sublayer farther away from the nucleation layer.

3. The gallium nitride epitaxial structure according to claim 1, characterized in that, Each of the stress relief layers includes a plurality of stress relief sublayers.

4. The gallium nitride epitaxial structure according to claim 1, characterized in that, The plurality of stress relief layers include a first stress relief layer and a second stress relief layer disposed on the side of the first stress relief layer opposite to the nucleation layer; The first stress relief layer includes a first stress relief sublayer and a second stress relief sublayer disposed on the side of the first stress relief sublayer away from the nucleation layer. The second stress relief layer includes a third stress relief sublayer and a fourth stress relief sublayer disposed on the side of the third stress relief sublayer away from the nucleation layer. The molar content of the first element in the first stress-relieving sublayer is less than the molar content of the first element in the second stress-relieving sublayer. The molar content of the first element in the third stress-relieving sublayer is less than the molar content of the first element in the fourth stress-relieving sublayer. The molar content of the first element in the first stress-relieving sublayer is greater than the molar content of the first element in the fourth stress-relieving sublayer.

5. The gallium nitride epitaxial structure according to claim 1, characterized in that, The stress conditioning layer further includes a buffer layer located between two adjacent stress relief layers.

6. The gallium nitride epitaxial structure according to claim 5, characterized in that, The buffer layer includes a plurality of buffer sub-layers stacked along the first direction; The molar content of the first element in the buffer sublayer closer to the nucleation layer is greater than the molar content of the first element in the buffer sublayer farther away from the nucleation layer.

7. The gallium nitride epitaxial structure according to claim 1, characterized in that, The epitaxial layer includes a channel layer, an insertion layer, and a barrier layer stacked sequentially along the first direction.

8. The gallium nitride epitaxial structure according to claim 1, characterized in that, The gallium nitride epitaxial structure further includes a high-resistivity voltage-resistant layer, which is disposed between the stress-adjusting layer and the epitaxial layer.

9. The gallium nitride epitaxial structure according to claim 1, characterized in that, The gallium nitride epitaxial structure further includes a cap layer, which is disposed on the side of the epitaxial layer opposite to the substrate layer.

10. A method for fabricating a gallium nitride epitaxial structure, characterized in that, Includes the following steps: Provide a substrate layer; A nucleation layer is formed on one side of the substrate layer along the first direction; A stress-regulating layer is formed on the side of the nucleation layer opposite to the substrate layer; An epitaxial layer is formed on the side of the stress-adjusting layer opposite to the substrate layer; Both the nucleation layer and the stress-regulating layer include a first element; The stress conditioning layer includes a plurality of stress relief layers stacked along the first direction, wherein at least one of the stress relief layers includes a plurality of stress relief sub-layers stacked along the first direction. In the plurality of stress relief layers, the molar content of the first element in the stress relief layer closer to the nucleation layer is greater than the molar content of the first element in the stress relief layer farther away from the nucleation layer; In the same stress relief layer, at least one stress relief sublayer has a first element molar content that is less than that of the stress relief sublayer further away from the nucleation layer.

Images