Nitride epitaxial structure and semiconductor device

Abstract

The application provides a nitride epitaxial structure, including: a substrate; a nucleation layer formed on the substrate, the nucleation layer being an aluminum nitride layer or a gallium nitride layer; a buffer layer formed on the nucleation layer, the buffer layer including K stacked III-V nitride double-layer structures, K being greater than or equal to 3; each double-layer structure including a stacked upper layer and a lower layer, a band gap difference of each double-layer structure being a difference between a band gap width of the upper layer and a band gap width of the lower layer; the band gap differences of the K double-layer structures overall presenting a gradual change trend along a thickness direction of the buffer layer; and an epitaxial layer formed on the buffer layer, a material of the epitaxial layer including III-V nitride. By setting the buffer layer with the multiple double-layer structures with gradually changed band gap differences, lattice mismatch between the substrate and the epitaxial layer can be effectively relieved, and crystal quality and voltage resistance performance can be well balanced, so that the performance of a semiconductor device is effectively improved. The application also provides a semiconductor device including the nitride epitaxial structure.

Description

Technical Field

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

[0002] Gallium nitride (GaN) materials are widely used in power electronic devices, radio frequency devices, and optoelectronic devices due to their large bandgap and high mobility. The most widespread application is in high electron mobility transistors (HEMTs). GaN materials are typically grown epitaxially on silicon substrates. However, due to a large lattice mismatch (over 17%) and thermal expansion coefficient mismatch between GaN and silicon, significant stress exists in silicon-based GaN. This stress causes warping during epitaxy, affecting the uniformity and reliability of the GaN epitaxial wafer. Moreover, the effect of warping becomes more significant with increasing substrate size. Currently, existing technologies mainly use graded AlGaN structures and superlattice structures to control stress. However, graded AlGaN structures suffer from poor dynamic performance and low crystal quality. While superlattice structures offer better stress control and crystal quality than graded AlGaN structures, it is difficult to balance voltage withstand performance and crystal quality. Summary of the Invention

[0003] In view of this, embodiments of this application provide a nitride epitaxial structure and a semiconductor device. By providing a buffer layer with a specific structure between the substrate and the epitaxial layer, the stress caused by lattice mismatch and thermal mismatch between the substrate and the epitaxial layer can be effectively relieved and released, reducing warpage during and after epitaxy, and improving the uniformity and reliability of the nitride epitaxial structure. It can also improve the crystal quality and voltage withstand performance of the epitaxial layer, thereby effectively improving the performance of the semiconductor device.

[0004] Specifically, the first aspect of this application provides a nitride epitaxial structure, including:

[0005] Substrate;

[0006] A nucleation layer is formed on the substrate, wherein the nucleation layer is an aluminum nitride layer or a gallium nitride layer;

[0007] A buffer layer is formed on the nucleation layer, the buffer layer comprising K stacked group III nitride bilayer structures, where K ≥ 3; each bilayer structure comprises a stacked upper layer and a lower layer, the bandgap of the upper layer material being greater than the bandgap of the lower layer material; the bandgap difference of each bilayer structure is the difference between the bandgap of the upper layer material and the bandgap of the lower layer material; the bandgap difference of the K bilayer structures generally exhibits a gradual trend along the thickness direction of the buffer layer;

[0008] An epitaxial layer is formed on the buffer layer, and the material of the epitaxial layer includes group III nitrides.

[0009] The nucleation layer provides nucleation centers for the subsequent growth of nitride epitaxial layers, alleviating lattice mismatch between the substrate and the epitaxial layer. It also effectively blocks impurities from the substrate from affecting the growth of the subsequent nitride epitaxial layer, improving the crystal quality of the epitaxial layer. The buffer layer, positioned between the substrate and the epitaxial layer, effectively alleviates stress caused by lattice and thermal mismatch between them, reducing warpage during and after epitaxy, and improving the uniformity and reliability of the nitride epitaxial structure. Furthermore, the buffer layer, constructed as a stack of multiple Group III nitride bilayer structures with varying band gaps, exhibits good dynamic performance, effectively balancing crystal quality and voltage withstand performance, reducing leakage risk, and thus effectively improving the performance of semiconductor devices. Moreover, by adaptively employing bilayer structures with different band gaps at different locations, the advantages of dislocation filtering and improved voltage withstand performance can be simultaneously achieved, finding a balance between the two performance characteristics according to actual needs. Dynamic performance generally refers to the transistor's recovery capability after increased electrical stress, which can be measured by indicators such as Dron (dynamic resistance).

[0010] In this embodiment of the application, in each double-layer structure, the materials of the upper layer and the lower layer are respectively selected from GaN, AlN, InN, or combinations thereof such as AlGaN, InGaN, InAlN, and InAlGaN. Specifically, the upper / lower layer material composition of the double-layer structure can be AlN / GaN, AlGaN / GaN, AlN / AlGaN, or AlGaN / AlGaN.

[0011] In this embodiment, the thickness of the lower layer is greater than twice the thickness of the upper layer. By setting relatively thick lower and upper layers, lattice relaxation can be effectively avoided. For heteroepitaxial growth, when the thickness of the upper layer is small, the material is in a state of strain, that is, the lattice constant of the upper layer material is stretched or compressed by the lower layer material and then remains consistent with the lower layer material, thus effectively functioning; while when the thickness of the upper layer is large, the material will recover to its own lattice constant, resulting in lattice relaxation.

[0012] In this embodiment, the band gap difference of the K bilayer structures gradually decreases from the nucleation layer side to the epitaxial layer side. When the band gap difference is large, the large difference in lattice constants between the materials of the bilayer structures is beneficial for filtering dislocations, but at the same time, the strong polarization effect can easily lead to leakage current. Conversely, when the band gap difference is small, it is beneficial for reducing leakage current, but not for filtering dislocations. By placing the bilayer structure with a large band gap difference closer to the nucleation layer side, it is beneficial for annihilating dislocations in the early stage of epitaxy and reducing the impact of leakage current; while placing the bilayer structure with a small band gap difference closer to the epitaxial layer side is beneficial for reducing leakage current and improving withstand voltage performance.

[0013] In this embodiment, among the K bilayer structures, the difference between the maximum and minimum bandgap difference is greater than 20% of the bandgap difference between the Group III nitride with the largest bandgap and the Group III nitride with the smallest bandgap constituting the bilayer structure. By controlling the difference between the maximum and minimum bandgap difference of the K bilayer structures in the entire buffer layer within a suitable range, the crystal quality and voltage withstand performance can be better balanced and adjusted.

[0014] In this embodiment, the K bilayer structures are composed of two Group III nitrides, GaN and AlN, and the average Al content in each bilayer structure is 5%-50%. The average Al content refers to the average molar percentage of Al element among Group III metal elements in each bilayer structure. Controlling the Al content of each bilayer structure within a suitable range ensures that the buffer layer has good crystal quality.

[0015] In this embodiment, the average Al content is the same in each of the bilayer structures. By keeping the Al content constant, it is possible to simplify parameter design by considering only the influence of film thickness when designing pre-compensation for high-temperature warpage, without having to consider the influence of Al composition variations.

[0016] In this embodiment, the average Al content of the K bilayer structures gradually changes along the thickness direction of the buffer layer. Designing the average Al content of multiple bilayer structures to be gradually varied is beneficial for stress control.

[0017] In this embodiment, any two adjacent double-layer structures can have different bandgap differences, or some adjacent double-layer structures can have the same bandgap difference. The repetition period of adjacent double-layer structures with the same bandgap difference can be 1-10.

[0018] In this embodiment of the application, to avoid relaxation, the thickness of each of the two-layer structures is set to be less than 100 nm.

[0019] In this embodiment of the application, the material of the epitaxial layer includes one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN.

[0020] In this application embodiment, the thickness of the epitaxial layer is greater than or equal to 300 nm. Existing gallium nitride epitaxial layers are generally small in thickness due to stress limitations, while the nitride epitaxial wafers of this application embodiment can effectively eliminate stress, thus theoretically allowing for infinite thickness. In some embodiments of this application, the thickness of the epitaxial layer can be greater than or equal to 5 μm, or greater than or equal to 10 μm.

[0021] In the embodiments of this application, the substrate includes a silicon substrate, a sapphire substrate, a silicon-on-insulator (SOI) substrate, a gallium nitride substrate, a gallium arsenide substrate, an indium phosphide substrate, an aluminum nitride substrate, a silicon carbide substrate, a quartz substrate, or a diamond substrate.

[0022] In this embodiment of the application, the thickness of the nucleation layer is 10nm-300nm.

[0023] In this embodiment, the nitride epitaxial structure further includes a transition layer disposed between the nucleation layer and the epitaxial layer, the transition layer being made of AlGaN. In this embodiment, the transition layer and the nucleation layer are made of the same material. In this embodiment, the thickness of the transition layer is 10nm-300nm.

[0024] In this embodiment of the application, the nitride epitaxial structure further includes other functional layers disposed on the epitaxial layer. The other functional layers can be set according to actual application needs, and may specifically include AlN insertion layer, AlGaN blocking layer, P-type GaN layer, etc.

[0025] Secondly, embodiments of this application also provide a semiconductor device, including the nitride epitaxial structure described in the first aspect of this application. The semiconductor device can be a power device, a radio frequency device, or an optoelectronic device. Specifically, it can be a field-effect transistor, a light-emitting diode, a laser diode, etc.

[0026] The nitride epitaxial structure provided in this application, by setting a nucleation layer on the substrate and a buffer layer on the nucleation layer, can effectively alleviate and release the stress caused by lattice mismatch and thermal mismatch between the substrate and the epitaxial layer, reduce warpage during and after epitaxy, improve the uniformity and reliability of the nitride epitaxial structure, and thus improve the performance of the semiconductor device. The semiconductor device provided in this application, by employing the nitride epitaxial structure provided in this application, can obtain a large-size, thick nitride epitaxial layer device, which can effectively reduce device cost and improve device performance. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the nitride epitaxial structure provided in one embodiment of this application;

[0028] Figure 2 This is a schematic diagram of the nitride epitaxial structure provided in another embodiment of this application;

[0029] Figure 3 This is a schematic diagram of the nitride epitaxial structure provided in another embodiment of this application;

[0030] Figure 4 This is a schematic diagram of the structure of the buffer layer in one embodiment of this application;

[0031] Figure 5 This is a schematic diagram of the nitride epitaxial structure provided in one embodiment of this application;

[0032] Figure 6 This is a process flow diagram of the preparation of nitride epitaxial structures provided in the embodiments of this application;

[0033] Figure 7A The image shows the TEM (Transmission Electron Microscope) pattern of the double-layer structure of the buffer layer near the substrate in the nitride epitaxial structure of Example 2.

[0034] Figure 7B The image shows the EDS (Energy Dispersive Spectroscopy) spectrum of the bilayer structure of the buffer layer near the substrate in the nitride epitaxial structure of Example 2.

[0035] Figure 8A This is a TEM image of the double-layer structure of the buffer layer near the epitaxial layer in the nitride epitaxial structure of Example 2;

[0036] Figure 8B The image shows the EDS spectrum of the bilayer structure of the buffer layer near the epitaxial layer in the nitride epitaxial structure of Example 2. Detailed Implementation

[0037] The embodiments of this application will now be described in conjunction with the accompanying drawings.

[0038] See Figure 1 and Figure 2This application provides a nitride epitaxial structure 100, including a substrate 10, a nucleation layer 20, a buffer layer 30, and an epitaxial layer 40. The nucleation layer 20 is an AlN layer or a GaN layer, formed on the substrate 10. The buffer layer 30 is formed on the nucleation layer 20, and the epitaxial layer 40 is formed on the buffer layer 30. The material of the epitaxial layer 40 includes a group III nitride. The buffer layer 30 includes K stacked group III nitride bilayer structures 200, where K ≥ 3. Each bilayer structure 300 includes a lower layer 301 and an upper layer 302. The bandgap of the upper layer 302 is greater than the bandgap of the lower layer 301, thus forming a bandgap difference. The bandgap difference of each bilayer structure 300 is the difference between the bandgap of the upper layer 302 and the bandgap of the lower layer 301. The bandgap difference of the K bilayer structures generally exhibits a gradual trend along the thickness direction of the buffer layer 30. The nitride epitaxial structure provided in this application has good epitaxial layer uniformity and high crystal quality, and can be applied in semiconductor devices to improve device performance. This nitride epitaxial structure can have a nitride epitaxial layer with a size of 6 inches or more and a thickness of 5 micrometers or more, meeting the requirements for large-size epitaxial structures.

[0039] It should be noted that in the bilayer structure of this application, "upper" and "lower" do not represent specific orientations. In this field, for superlattice bilayer structures, the layer with the larger bandgap is generally written as the upper layer and the layer with the smaller bandgap as the lower layer. Even if the order of the two layers is interchanged during actual growth, it will not be reversed when writing the structure.

[0040] In this embodiment, the substrate 10 can be a silicon substrate, a sapphire substrate, a silicon-on-insulator (SOI) substrate, a gallium nitride substrate, a gallium arsenide substrate, an indium phosphide substrate, an aluminum nitride substrate, a silicon carbide substrate, a quartz substrate, or a diamond substrate, or any known substrate that can be used to prepare group III nitride thin films. The crystal orientation of the silicon substrate is not limited; for example, it can be a silicon substrate with a (111) crystal plane index, a silicon substrate with a (100) crystal plane index, or a silicon substrate with other crystal plane indices.

[0041] In this embodiment, the nucleation layer 20 is a thin film of aluminum nitride or gallium nitride, completely covering the substrate 10. The nucleation layer 20 provides nucleation centers for the subsequent growth of the nitride epitaxial layer and alleviates the stress caused by lattice mismatch between the substrate 10 and the epitaxial layer 40. It also effectively blocks impurities from the substrate 10 from affecting the growth of the subsequent nitride epitaxial layer, reducing lattice defects, lowering dislocation density, and improving the crystal quality of the nitride epitaxial layer. Furthermore, the nucleation layer 20 is relatively thin, being single-crystal or quasi-single-crystal, thus alleviating the stress caused by lattice mismatch between the substrate 10 and the epitaxial layer 40, without affecting the crystal quality of the subsequent nitride epitaxial layer, and effectively controlling costs. In some embodiments of this application, the thickness of the nucleation layer 20 can be 10nm-300nm. In other embodiments, the thickness of the nucleation layer 20 can be 20nm-200nm. In still other embodiments, the thickness of the nucleation layer 20 can be 50nm-150nm.

[0042] In this embodiment, the nucleation layer 20 can be prepared by metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy. MOCVD is a chemical vapor deposition technique that utilizes the thermal decomposition reaction of organometallic compounds to grow thin films in the vapor phase. Specifically, organometallic compounds such as organic compounds of group III and group II elements and hydrides of group V and VI elements can be used as crystal growth source materials to grow group III-V and group II-VI compound thin films on a substrate through thermal decomposition reactions. MOCVD can improve the crystal quality of the subsequent epitaxial nitride layer.

[0043] In this embodiment, the buffer layer 30 includes K stacked Group III nitride bilayer structures 300. In some embodiments, K can be 3-100. In other embodiments, K can be 10-60. In still other embodiments, K can be 20-50. In each bilayer structure, the upper layer 302 and the lower layer 301 can be made of GaN, AlN, InN, or combinations thereof, such as AlGaN, InGaN, InAlN, and InAlGaN. Specifically, AlGaN is composed of two Group III nitrides, GaN and AlN; InGaN is composed of two Group III nitrides, GaN and InN; InAlN is composed of two Group III nitrides, AlN and InN; and InAlGaN is composed of three Group III nitrides, GaN, AlN, and InN. Among them, GaN has a bandgap of 3.4 eV, AlN has a bandgap of 6.2 eV, and InN has a bandgap of 0.7 eV. Specifically, the upper / lower layer material composition of the double-layer structure 300 can be AlN / GaN, AlGaN / GaN, AlN / AlGaN, or AlGaN / AlGaN.

[0044] In this embodiment, the thickness of the buffer layer 30 can be set according to the withstand voltage rating. For example, for a withstand voltage rating of 100V, the buffer layer generally needs to be set to 2μm-3μm, while for a withstand voltage rating of 600V, the buffer layer needs to be set to 5μm or more. In some embodiments of this application, the thickness of the buffer layer 30 is greater than 300nm. Specifically, the thickness of each bilayer structure is less than 100nm, and can be 10nm-80nm or 20nm-60nm. A suitable bilayer structure thickness helps to avoid relaxation. In each bilayer structure 300, the thickness of the lower layer 301 is greater than twice the thickness of the upper layer 302. By setting relatively thick lower and upper layers, lattice relaxation can be effectively avoided. For heteroepitaxial growth, when the upper layer thickness is small, the material is in a strained state, meaning that the lattice constant of the upper material is stretched or compressed by the lower material and remains consistent with the lower material, thus effectively exerting the superlattice effect; while when the upper layer thickness is large, the material will recover to its own lattice constant, resulting in lattice relaxation. In K double-layer structures 300, the thickness of each upper layer can be equal, and the thickness of each lower layer can be equal.

[0045] In some embodiments of this application, the band gap difference of the K bilayer structures 300 gradually decreases from the nucleation layer 200 side to the epitaxial layer 400 side. When the band gap difference is large, the large difference in lattice constants between the materials of the bilayer structures is beneficial for filtering dislocations, but at the same time, the strong polarization effect can easily lead to leakage current. Conversely, when the band gap difference is small, it is beneficial for reducing leakage current, but not for filtering dislocations. By placing the bilayer structure with a large band gap difference closer to the nucleation layer, it is beneficial for filtering dislocations, and at the same time, because it is far from the AlGaN barrier layer and channel layer, the adverse effects of leakage current are smaller. Conversely, placing the bilayer structure with a small band gap difference closer to the epitaxial layer is beneficial for reducing the polarization effect and improving the breakdown voltage performance. In other embodiments, the K bilayer structures 300 may be arranged as needed, with the band gap difference gradually increasing from the nucleation layer 200 side to the epitaxial layer 400 side.

[0046] In this embodiment, among the K bilayer structures, the difference between the maximum and minimum bandgap differences is greater than 20% of the difference between the bandgap widths of the Group III nitride with the largest and smallest bandgap widths constituting the bilayer structure. For example, in the K AlGaN / AlGaN bilayer structures, the Group III nitrides constituting the bilayer structure include GaN and AlN, where the bandgap width of GaN is 3.4 eV and the bandgap width of AlN is 6.2 eV. Therefore, 20% of the difference between the bandgap widths of the Group III nitride with the largest and smallest bandgap widths constituting the bilayer structure is 20% × (6.2 - 3.4) eV. For example, in K InAlGaN / InAlGaN bilayer structures, the Group III nitrides constituting the bilayer structure include InN, GaN, and AlN. The band gap of InN is 0.7 eV, the band gap of GaN is 3.4 eV, and the band gap of AlN is 6.2 eV. Then, 20% of the difference between the band gap of the Group III nitride with the largest band gap and the group III nitride with the smallest band gap constituting the bilayer structure is 20% × (6.2 - 0.7) eV.

[0047] In some embodiments of this application, the K bilayer structures 200 are composed of two Group III nitrides, GaN and AlN, and the composition of the upper / lower layer of the bilayer structure can be represented as Al x Ga 1-x N / Al y Ga 1-yN(0<x≤1,y> 0). The gradual change in band gap of this bilayer structure is equivalent to the gradual change in the difference in Al content. Since the band gap variation trend is approximately linearly related to the Al content in AlGaN (i.e., the higher the Al content in AlGaN, the larger the band gap), the gradual change in band gap of the bilayer structure is equivalent to the gradual change in the difference in Al content. It should be noted that in this application, Al content refers to the molar percentage of Al among Group III metals. For Al... x Ga 1-x N, whose bandgap can be approximately equal to [6.2x + (1-x)3.4] eV. Therefore, by controlling the Al component content of the upper and lower layers in each bilayer structure, so that the difference in Al component content of the bilayer structure shows a gradual trend, the bandgap difference of K bilayer structures can be gradually varied. For example, as Figure 2 and Figure 3 As shown, the K double-layer structures 200 include the first double-layer structure A1 x1 Ga 1-x1 N / Al y1 Ga 1-y1 N, the second double-layer structure Al x2 Ga 1-x2 N / Al y2 Ga 1-y2 N, third double-layer structure Al x3 Ga 1-x3 N / Al y3 Ga 1-y3 N……and the Kth double-layer structure Al xk Ga 1-xk N / Al yk Ga 1-yk N. If the band gap difference gradually decreases from the first bilayer structure to the Kth bilayer structure, then x1-y1>x2-y2>x3-y3>…>xk-yk, that is, the difference in Al component content gradually decreases from the first bilayer structure to the Kth bilayer structure. In this embodiment, any two adjacent bilayer structures have different band gap differences. Specifically, any two adjacent bilayer structures have different component compositions. In other embodiments of this application, among the K bilayer structures, some adjacent bilayer structures may have the same band gap difference. The repetition period of adjacent stacked bilayer structures with the same band gap difference can be 1-10. The repetition periods for bilayer structures with different band gap differences can be the same or different, for example, such as… Figure 4 As shown, in Al x Ga 1-x N / Al y Ga 1-yIn a buffer layer composed of N layers, the repetition period of bilayer structures with different band gaps is the same, which is 2. That is, the band gap difference of the first bilayer structure = the band gap difference of the second bilayer structure > the band gap difference of the third bilayer structure = the band gap difference of the fourth bilayer structure, ... > the band gap difference of the Kth bilayer structure. The repetition periods of bilayer structures with different band gaps are not the same. For example, the band gap difference of the first bilayer structure = the band gap difference of the second bilayer structure = the band gap difference of the third bilayer structure > the band gap difference of the fourth bilayer structure = the band gap difference of the fifth bilayer structure > the band gap difference of the sixth bilayer structure, ... > the band gap difference of the Kth bilayer structure.

[0048] In this embodiment, the K bilayer structures are composed of two Group III nitrides, GaN and AlN, and the average Al content in each bilayer structure can be 5%-50%. In some embodiments, the average Al content in each bilayer structure is 8%-38%. In other embodiments, the average Al content in each bilayer structure is 15%-30%. In still other embodiments, the average Al content in each Group III nitride bilayer structure is 20%-25%. The average Al content refers to the average molar percentage of Al element among Group III metal elements in each bilayer structure. Controlling the average Al content of each bilayer structure within a suitable range can ensure that the buffer layer has good crystal quality. For Al... x Ga 1-x N / Al y Ga 1-y The N-layer structure, the average Al component content in each layer can be expressed as [(T 上 ×x+T 下 ×y) / (T 上 +T 下 )]×100%, where T 上 and T 下 Let x and y represent the thicknesses of the upper and lower layers of the bilayer structure, respectively, and let x and y represent the Al content of the upper and lower layers, respectively. In some embodiments of this application, the average Al content in each bilayer structure is the same. By keeping the Al content constant, when designing pre-compensation for high-temperature warpage, only the influence of film thickness needs to be considered, without considering the influence of Al content changes, thus simplifying parameter design. In other embodiments of this application, the average Al content of the K bilayer structures gradually changes along the thickness direction of the buffer layer. Designing the average Al content of multiple bilayer structures to be gradually changing is beneficial for stress control.

[0049] In addition, the band gap difference of the K double-layer structures in this application generally exhibits a gradual trend along the thickness direction of the buffer layer. It can be a strict gradual increase or decrease along the thickness direction of the buffer layer, or it can be a gradual increase or decrease overall. However, there are a few special cases that are opposite to the overall gradual trend. For example, in a buffer layer where the band gap difference is gradually increasing overall, there are a few double-layer structures with decreasing band gap difference.

[0050] In this application embodiment, the epitaxial layer material includes one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN. In this application embodiment, the epitaxial layer 40 material includes Group III nitrides, specifically, for example, one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN. The thickness of the epitaxial layer 40 is greater than or equal to 300 nm. Existing gallium nitride epitaxial layers are generally thin due to stress limitations, while the nitride epitaxial structure of this application embodiment can effectively eliminate stress, thus it is suitable for the fabrication of thick-film epitaxial layers, theoretically allowing for unlimited thickness. In some embodiments of this application, the thickness of the epitaxial layer can be greater than or equal to 5 μm, or greater than or equal to 10 μm, for example, 15 μm-100 μm. The epitaxial layer 40 can completely cover the nucleation layer 20, or it can partially cover the nucleation layer 20.

[0051] In the embodiments of this application, different nitride epitaxial layers can be used for different semiconductor devices. For example, GaN, AlGaN, and AlN can be used for power devices, while In-containing nitride epitaxial layers can be used for optoelectronic devices.

[0052] In this embodiment of the application, other elements may be incorporated into the epitaxial layer 40 to meet the performance requirements. For example, carbon may be incorporated to improve insulation, form high resistance, and improve withstand voltage performance.

[0053] like Figure 5 As shown, the nitride epitaxial structure 100 also includes a transition layer 50 disposed between the nucleation layer 30 and the epitaxial layer 40. The transition layer 50 can be an AlGaN layer. The thickness of the transition layer can be 10 nm to 300 nm. The provision of the transition layer 50 is beneficial for controlling the stress of the epitaxial structure.

[0054] In the embodiments of this application, such as Figure 5As shown, the nitride epitaxial structure 100 also includes other functional layers 60 disposed on the epitaxial layer 40. The specific structural composition of the other functional layers 60 can be set according to the actual application requirements. In one embodiment of this application, it may specifically include an AlN insertion layer 61, an AlGaN barrier layer 62, and a P-type GaN layer 63 sequentially disposed on the epitaxial layer 40. In some other embodiments, the other functional layers 60 may also have other structural compositions.

[0055] like Figure 6 As shown in the embodiments of this application, a method for preparing a nitride epitaxial structure is also provided, comprising:

[0056] S01. A nucleation layer is formed on the substrate, which is an AlN layer or a GaN layer.

[0057] Specifically, the nucleation layer 20 can be prepared on the substrate 10 using metal-organic chemical vapor deposition or molecular beam epitaxy. Before preparing the nucleation layer 20, the substrate 10 can be subjected to conventional cleaning treatment.

[0058] In one specific embodiment of this application, a nucleation layer 20 is prepared on a substrate 10 using metal-organic chemical vapor deposition (MOCVD). Specifically, the substrate 10 is placed in a MOCVD reaction chamber, and hydrogen and ammonia are introduced for 3-5 minutes at a temperature of 900-1100°C and a pressure of 30-60 Torr to obtain a treated substrate 10. Then, hydrogen, ammonia, and an aluminum or gallium source are introduced to deposit aluminum nitride or gallium nitride on the treated substrate 10, thus obtaining the nucleation layer 20. In this embodiment, the parameters in the deposition process are not limited to the above ranges. Gallium sources include, but are not limited to, trimethylgallium and triethylgallium. Aluminum sources include, but are not limited to, trimethylaluminum and triethylaluminum.

[0059] S02, forming a buffer layer on the nucleation layer.

[0060] In this embodiment, the buffer layer 30 can be prepared by metal-organic chemical vapor deposition (MOCVD). Specifically, the substrate with the nucleation layer obtained after step S01 is placed in a MOCVD reaction chamber at a temperature of 900-1100°C and a pressure of 30-60 Torr. Then, hydrogen, ammonia, and a Group III metal source are introduced to epitaxially grow Group III nitrides on the buffer layer 30, thus obtaining the buffer layer 30. The Group III metal source is an organic compound containing a Group III metal element, such as trimethylgallium, triethylgallium, trimethylaluminum, triethylaluminum, etc. By changing the amount of Group III metal source introduced, the content of each Group III nitride in the buffer layer can be changed, and by controlling the deposition time, nitride layers of different thicknesses can be obtained.

[0061] S03. Group III nitrides are epitaxially grown on the buffer layer to form an epitaxial layer.

[0062] In this embodiment, the epitaxial layer 40 can be prepared by metal-organic chemical vapor deposition (MOCVD). Specifically, the substrate 10 obtained after step S02 is placed in a MOCVD reaction chamber, and hydrogen and ammonia are introduced for 3-5 minutes at a temperature of 900-1100°C and a pressure of 30-60 Torr to obtain the treated substrate 10. Then, hydrogen, ammonia, and a Group III metal source are introduced to epitaxially grow a Group III nitride on the buffer layer 30, forming the epitaxial layer 40. The Group III nitride can specifically be one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN. The Group III metal source is an organic compound containing a Group III metal element, such as trimethylgallium, triethylgallium, trimethylaluminum, or triethylaluminum.

[0063] In this embodiment of the application, the above-described preparation method may further include forming a transition layer 50 between the buffer layer 30 and the epitaxial layer 40. That is, before step S03, a transition layer 50 is first prepared on the buffer layer 30, and then the epitaxial layer 40 is grown on the transition layer 50. The transition layer 50 may be made of Al GaN.

[0064] This application also provides a semiconductor device, including the nitride epitaxial structure provided in the embodiments of this application. The nitride epitaxial structure can be directly used as part of the semiconductor device, or it can be peeled off and applied to the semiconductor device. The semiconductor device includes, but is not limited to, power devices (i.e., power electronic devices), radio frequency devices, or optoelectronic devices. Power devices and radio frequency devices can be transistors, specifically field-effect transistors, such as high electron mobility transistors (HEMTs). Optoelectronic devices include, for example, light-emitting diodes (LEDs) and laser diodes (LDs). Specifically, they can be nitride-based LEDs or nitride-based quantum well laser diodes.

[0065] The embodiments of this application will be further described below through multiple examples.

[0066] Example 1

[0067] A nitride epitaxial structure includes a substrate and a nucleation layer, a buffer layer, an epitaxial layer, and other functional layers sequentially disposed on the substrate. The substrate is made of materials such as Si, sapphire, GaN, SiC, diamond, or SOI; the nucleation layer is an AlN nucleation layer with a thickness between 50 nm and 400 nm; the buffer layer is a graded bandgap structure layer, including 11 upper / lower AlN nucleation layers. x Ga 1-x N / Al y Ga 1-y The N bilayer structure has an average Al content of 20% in each bilayer structure. The x, y values ​​and the thickness T of each bilayer structure are given. 上 T 下 As shown in Table 1, the epitaxial layer is a GaN layer, which may contain carbon-doped GaN or AlGaN structures, with a thickness of 100 nm to 3 μm. Other functional layers may include an AlN insertion layer sequentially disposed on the epitaxial layer, with a thickness of 1 nm; an AlGaN barrier layer, with an Al composition ranging from 10% to 30% and a thickness of 10 to 30 nm; and a p-GaN layer, where p-type impurities are achieved through Mg doping, with a thickness ranging from 30 nm to 120 nm.

[0068] Table 1 Buffer layer parameters of Example 1

[0069]

[0070]

[0071] In this arrangement, the bilayer structures numbered 1-11 are stacked sequentially, with the bilayer structure numbered 1 positioned closer to the epitaxial layer and the bilayer structure numbered 11 positioned closer to the nucleation layer. The period number 5 in Table 1 indicates that each bilayer structure is repeated 5 times; that is, the repetition period of bilayer structures with different band gaps is the same, forming 11 groups of bilayer structures, each group consisting of 5 identical stacked bilayer structures. In other words, the buffer layer comprises 5 stacked Al... 0.5 Ga 0.5 N / Al 0.17 Ga 0.83 N double-layer structure, 5 stacked Al 0.55 Ga 0.45 N / Al 0.165 Ga 0.835 N-layer structure...and so on. Table 1 shows that in the nitride epitaxial structure of Example 1, the Al content difference of the 11 groups of bilayer structures in the buffer layer gradually decreases from the nucleation layer side to the epitaxial layer side; that is, the band gap difference of the 11 groups of bilayer structures gradually decreases from the nucleation layer side to the epitaxial layer side. Furthermore, the average Al content of each group of bilayer structures in Example 1 is the same, at 20%.

[0072] Example 2

[0073] The only difference from Example 1 is that the buffer layer includes 51 upper / lower layers of Al. x Ga 1-x N / Al y Ga 1-y N has a double-layer structure, where the x and y values ​​and the upper layer thickness T are in each double-layer structure. 上 The thickness of the lower layer T 下 As shown in Table 2.

[0074] Table 2 Buffer layer parameters of Example 2

[0075]

[0076]

[0077] In this embodiment, the bilayer structures numbered 1-51 are stacked sequentially, with the bilayer structure numbered 1 positioned closer to the epitaxial layer and the bilayer structure numbered 51 positioned closer to the nucleation layer. The period number 1 in Table 2 indicates that there is only one bilayer structure for each number. Table 2 shows that in the nitride epitaxial structure of Example 2, the Al content difference among the 51 bilayer structures in the buffer layer gradually decreases from the nucleation layer side to the epitaxial layer side; that is, the bandgap difference among the 51 bilayer structures gradually decreases from the nucleation layer side to the epitaxial layer side. Furthermore, the average Al content of each bilayer structure in Example 2 is the same, at 20%. Compared to Example 1, the bandgap difference gradient spacing of the buffer layer in Example 2 is smaller, which better adjusts the stress between the substrate and the epitaxial layer.

[0078] Figure 7A This is a TEM image of the bilayer structure of the buffer layer near the substrate in the nitride epitaxial structure of Example 2. Figure 7B The image shows the EDS spectrum of the double-layer structure of the buffer layer near the substrate in the nitride epitaxial structure of Example 2. Figure 7B The double-layer structure in the table corresponds to the three double-layer structures numbered 49-51 in Table 2, which are composed of... Figure 7A and Figure 7B It can be seen that in the bilayer structure near the substrate, the upper layer with a large band gap has an Al content close to 100%, and the content decreases towards the side away from the substrate. Figure 8A This is a TEM image of the bilayer structure of the buffer layer near the epitaxial layer in the nitride epitaxial structure of Example 2. Figure 8B The image shows the EDS spectrum of the bilayer structure of the buffer layer near the epitaxial layer in the nitride epitaxial structure of Example 2. Figure 8B The double-layer structure in the table corresponds to the three double-layer structures numbered 1-3 in Table 2. (Comparison) Figure 7B and Figure 8BIt can be seen that the difference in Al content in the bilayer structure closer to the substrate is greater than the difference in Al content in the bilayer structure closer to the epitaxial layer.

[0079] Note: The EDS spectrum contains curves for Ga, Al, and N elements. N element accounts for approximately 50%, so the ordinate value of each point on the Al element curve multiplied by 2 represents the Al component content. Due to measurement errors and other factors, the measured value may differ from the design value.

[0080] Example 3

[0081] The difference from Embodiment 1 is that the buffer layer includes 11 sets of upper / lower layers of Al. x Ga 1-x N / Al y Ga 1-y N has a double-layer structure, where the x and y values ​​and the upper layer thickness T are in each double-layer structure. 上 The thickness of the lower layer T 下 As shown in Table 3.

[0082] Table 3 Buffer layer parameters of Example 3

[0083]

[0084] In this arrangement, the bilayer structures numbered 1-11 are stacked sequentially, with the bilayer structure numbered 1 positioned closer to the epitaxial layer and the bilayer structure numbered 11 positioned closer to the nucleation layer. The period number 5 in Table 1 indicates that each bilayer structure is repeated 5 times, meaning that the repetition period for bilayer structures with different band gaps is the same, forming 11 sets of bilayer structures, each set consisting of 5 identical stacked bilayer structures. Table 3 shows that in the nitride epitaxial structure of Example 3, the Al component content difference of the 11 sets of bilayer structures in the buffer layer gradually decreases from the nucleation layer side to the epitaxial layer side; that is, the band gap difference of the 11 bilayer structures gradually decreases from the nucleation layer side to the epitaxial layer side. Furthermore, the average Al component content of the 11 sets of bilayer structures in Example 3 also gradually decreases from the nucleation layer side to the epitaxial layer side.

Claims

1. A nitride epitaxial structure, characterized in that, include: Substrate; A nucleation layer is formed on the substrate, wherein the nucleation layer is an aluminum nitride layer or a gallium nitride layer; A buffer layer is formed on the nucleation layer, the buffer layer comprising K stacked group III nitride bilayer structures, where K ≥ 3; each bilayer structure comprises a stacked upper layer and a lower layer, the bandgap of the upper layer material being greater than the bandgap of the lower layer material; the bandgap difference of each bilayer structure is the difference between the bandgap of the upper layer material and the bandgap of the lower layer material; the bandgap difference of the K bilayer structures generally exhibits a gradual trend along the thickness direction of the buffer layer; the K bilayer structures are composed of GaN and AlN, and the average Al content in each bilayer structure is 15%-50%; the average Al content in each bilayer structure is the same; or the average Al content of the K bilayer structures gradually decreases from the nucleation layer side to the epitaxial layer side; An epitaxial layer is formed on the buffer layer, and the material of the epitaxial layer includes group III nitrides.

2. The nitride epitaxial structure as described in claim 1, characterized in that, The materials of the upper and lower layers are respectively selected from GaN, AlN, InN, or combinations thereof.

3. The nitride epitaxial structure as described in claim 1 or 2, characterized in that, The thickness of the lower layer is greater than twice the thickness of the upper layer.

4. The nitride epitaxial structure as described in claim 1, characterized in that, The band gap difference of the K bilayer structures gradually decreases from the nucleation layer side to the epitaxial layer side.

5. The nitride epitaxial structure as described in claim 1, characterized in that, In the K bilayer structures, the difference between the maximum bandgap difference and the minimum bandgap difference is greater than 20% of the difference between the bandgap width of the Group III nitride with the largest bandgap width and the bandgap width of the Group III nitride with the smallest bandgap width constituting the bilayer structure.

6. The nitride epitaxial structure as described in claim 1, characterized in that, The thickness of each of the described double-layer structures is less than 100 nm.

7. The nitride epitaxial structure as described in claim 1, characterized in that, The material of the epitaxial layer includes one or more of GaN, AlN, InN, AlGaN, InGaN, InAlN, and InAlGaN.

8. The nitride epitaxial structure as described in claim 1, characterized in that, The thickness of the epitaxial layer is greater than or equal to 300 nm.

9. The nitride epitaxial structure as described in claim 1, characterized in that, The substrate includes a silicon substrate, a sapphire substrate, a silicon-on-insulator substrate, a gallium nitride substrate, a gallium arsenide substrate, an indium phosphide substrate, an aluminum nitride substrate, a silicon carbide substrate, a quartz substrate, or a diamond substrate.

10. The nitride epitaxial structure as described in claim 1, characterized in that, The thickness of the nucleation layer is 10nm-300nm.

11. A semiconductor device, characterized in that, Including the nitride epitaxial structure as described in any one of claims 1-10.

12. The semiconductor device as claimed in claim 11, characterized in that, The semiconductor devices include power devices, radio frequency devices, or optoelectronic devices.

13. The semiconductor device as claimed in claim 11 or 12, characterized in that, The semiconductor device includes a field-effect transistor, a light-emitting diode, or a laser diode.

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