WO2022089182A1 - 具有2d材料中介层的氮化镓外延基板 - Google Patents

具有2d材料中介层的氮化镓外延基板 Download PDF

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WO2022089182A1
WO2022089182A1 PCT/CN2021/122990 CN2021122990W WO2022089182A1 WO 2022089182 A1 WO2022089182 A1 WO 2022089182A1 CN 2021122990 W CN2021122990 W CN 2021122990W WO 2022089182 A1 WO2022089182 A1 WO 2022089182A1
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aln
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王晓靁
施能泰
宋高梅
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王晓靁
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    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/0304—Inorganic materials including, apart from doping materials or other impurities, only AIIIBV compounds

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  • the present invention relates to a gallium nitride epitaxial substrate with a 2D material interposer.
  • epitaxy has an important impact on the quality of products.
  • the impact on quality includes component performance, yield, reliability and life.
  • the material of the substrate hopes to minimize the defect density of the single crystal material, and the crystal structure, lattice constant (lattice constant), and coefficient of thermal expansion (CTE, coefficient of thermal expansion) match the epitaxial material to avoid as much as possible in the epitaxy process. affect crystal quality.
  • the third-generation semiconductor technology and market have developed rapidly with the demand for power and high-frequency semiconductor components. The basis for quality improvement depends on the supply of high-quality epitaxial substrates of silicon carbide and gallium nitride, the two main protagonists of the third-generation semiconductor materials.
  • the most commonly used GaN substrates are GaN-on-Si and GaN-on-SiC. on-SiC) two substrates.
  • the current GaN crystal growth method adopts the hydride vapor phase epitaxy (HVPE) method to produce single crystal gallium nitride substrates. Due to the limitations of production cost and yield conditions, the current mass production The technology reaches 4-inch substrates and the cost is extremely high.
  • HVPE hydride vapor phase epitaxy
  • the defect density of the above-mentioned vapor phase method is still higher than that of other liquid phase crystallization processes, but it is limited by the slow growth rate of the remaining processes and the higher cost of mass production. Under the consideration of compromise, the mainstream of commercial transformation is still limited to the HVPE method.
  • the literature points out that the vapor phase GaN crystal growth rate is still possible to increase several times and maintain good crystallinity, but due to the deterioration of defect density, it has not been used as an orientation to reduce the cost of GaN substrates.
  • PVT physical vapor transport
  • one of the gas phase methods is used to produce single crystal aluminum nitride substrates.
  • SiC silicon carbide
  • SiC substrates are the current substrate materials for high-performance power semiconductors and high-end light-emitting diodes.
  • Transport, PVT high-quality large-size silicon carbide single crystal growth technology is difficult, high-end mass production technology is in the hands of a few manufacturers, and there is still a lot of room for improvement in the application cost.
  • Gallium nitride on silicon carbide is a high-quality GaN epitaxial substrate, but for the above reasons, large-scale substrates have problems such as high price, limited supply and technology in the hands of a few manufacturers; relatively In other words, due to the large size, low cost, high productivity and stable quality of silicon substrates, the development of gallium nitride (GaN-on-Si) substrates on silicon wafers is more commonly concerned by relevant manufacturers.
  • GaN-on-Si and GaN-on-SiC both belong to heterojunction epitaxy in terms of epitaxy process.
  • the higher quality of GaN-on-SiC than GaN-on-Si is precisely because of the GaN-on-SiC lattice
  • the degree of mismatch (lattice mismatch) is smaller than that of GaN-on-Si; another important feature is that the gallium nitride layer has significant tensile stress on the silicon surface.
  • Two-dimensional (2D) materials is a rapidly developing emerging field.
  • the earliest and most well-known material in the 2D material family that has attracted a lot of R&D investment is graphene, whose two-dimensional layered structure has special or Excellent physical/chemical/mechanical/optical properties, there is no strong bond between layers, only the van der Waals force, which also means that there is no dangling bond on the surface of the layered structure.
  • graphene has been It has been confirmed to have a wide range of excellent application potential; graphene research and development work is generally carried out around the world, and it also drives the research and development of more 2D materials, including hexagonal boron nitride hBN (hexagonal Boron Nitride), transition metal dichalcogenide TMDs (transition metal dichalcogenide TMDs (transition metal dichalcogenide) Metal dichalcogenides) and black phosphorus are also the ones who have accumulated more research and development achievements in the 2D material family.
  • Each of the above materials has specific material properties and application potential, and the manufacturing technology development of related materials is also actively promoted.
  • one of the TMDs materials are considered to have excellent diffusion barrier properties and varying degrees of high temperature stability.
  • hBN has excellent chemical passivation properties. Inertness and high temperature oxidation resistance.
  • van der Waals bonding characteristics of 2D materials have also attracted attention for the use of epitaxial substrates applied to traditional 3D materials. expansion) must be very well matched with the substrate material, but in reality, it often encounters situations such as the lack of suitable substrate materials for the subject of the present invention, or the ideal substrate material is expensive or difficult to obtain.
  • van der Waals Epitaxy Another solution, the so-called van der Waals Epitaxy.
  • the mechanism that van der Waals epitaxy may be beneficial to heteroepitaxy comes from the fact that the direct chemical bonds at the traditional epitaxy interface are replaced by van der Waals force bonding, which will relieve the stress or strain energy from the mismatch of lattice and thermal expansion in the epitaxy process to a certain extent.
  • the above-mentioned 2D layered material has a hexagon or honeycomb structure, and is considered to be structurally compatible with Wurtzite and Zinc-Blende structural materials in epitaxial time, and the related fields of the present invention are mainly Epitaxial materials belong to this type of structure.
  • single crystal is one of the requirements to ensure the quality of epitaxial crystals.
  • the growth of 2D materials tends to correlate with the crystal orientation of the crystalline substrate during the nucleation stage. It belongs to a polycrystalline structure, and the 2D material has already formed an inconsistent direction in the nucleation stage. After the nuclei aggregate into a continuous film with the growth, there are still domains with different orientations instead of single crystals; when the substrate is a single crystal material such as sapphire, it is still Due to the symmetry correlation between the two structures, the possible specific nucleation direction is not unique, and it is impossible to form a single crystal continuous film.
  • the two-dimensional material layer grown on the surface of high-quality sapphire is often transferred to other substrate surfaces through a transfer process; the two-dimensional material layer grown on the surface of high-quality sapphire is directly applied without transfer.
  • the possible quality effects of the two-dimensional material layer including defects, wrinkles and surface contamination residues from the transfer process can be avoided.
  • GaN-on-Si gallium nitride on silicon wafer
  • Heteroepitaxy needs to overcome the lattice matching problem between different materials, as well as the thermal stress problem caused by the different thermal expansion coefficients between the epitaxial layer and the substrate.
  • the GaN-on-Si lattice mismatch is relatively high, resulting in During the epitaxy process, the defect density of the gallium nitride layer is relatively high; another important feature is that the gallium nitride layer has significant tensile stress on the silicon surface.
  • the gallium nitride layer When the thickness of the gallium nitride layer is increased, the stress is higher, resulting in the bending deformation of the substrate or even nitriding The gallium layer may crack, and the associated effect becomes more severe as the wafer size increases. Relevant technical difficulties have led to the generally low yield of GaN-on-Si, and it is mostly used in power supply products. Currently, mass production is still dominated by six inches, and the advantages of large size of silicon wafers have not been fully utilized.
  • GaN-on-Sapphire of the existing process is shown in Figure 2. Heteroepitaxy needs to overcome the lattice matching problem between different materials, as well as the thermal stress problem caused by the different thermal expansion coefficients between the epitaxial layer and the substrate.
  • the degree of GaN-on-Sapphire lattice mismatch is high, resulting in epitaxy During the process, the defect density of the gallium nitride layer is at a certain level, and it still has an irreplaceable position under the long-term commercial technology development of light-emitting diodes; but in the field of high frequency and power semiconductors, due to the low thermal conductivity of sapphire, gallium nitride on sapphire ( GaN-on-Sapphire) applications are hindered.
  • the present invention provides a gallium nitride epitaxial substrate with a 2D material interposer.
  • a gallium nitride epitaxial substrate with a 2D material interposer includes a polycrystalline AlN substrate; the polycrystalline AlN substrate has a SiO2 bonding layer; the SiO2 bonding layer has a c-plane sapphire bonding layer; the c-plane sapphire bonding layer is on the A polycrystalline 2D material interposer is grown.
  • the polycrystalline 2D material interposer has at least one top layer, and the lattice constant of the top layer is highly matched with AlN, AlGaN or GaN; GaN single crystal is grown on the polycrystalline 2D material interposer by van der Waals epitaxy.
  • An AlN or AlGaN nucleation auxiliary layer is grown on the epitaxial layer, or a polycrystalline 2D material interlayer by van der Waals epitaxy, and a GaN single crystal epitaxial layer is formed on the AlN or AlGaN nucleation auxiliary layer.
  • the thickness of the 2D material interposer is greater than 0.5 nm.
  • the thickness of the c-plane sapphire bonding layer is greater than 10 nm.
  • the 2D material interposer is a 2D layer suitable for GaN, AlGaN or AlN epitaxy.
  • the 2D material interposer is a single-layer structure with only a top layer, and the top layer is a 2D material suitable for GaN, AlGaN or AlN epitaxy.
  • the 2D material interlayer is a composite layer structure formed by a top layer and a bottom layer, the top layer is a 2D material suitable for GaN, AlGaN or AlN epitaxy, and the bottom layer is a 2D material suitable for a single crystal base layer.
  • the top layer adopts WS 2 or MoS 2 ; the bottom layer adopts hBN.
  • the single-layer structure or composite-layer structure of the 2D material interposer has a mismatch of the top lattice constant a of AlN, AlGaN or GaN by no more than 20% and is suitable for AlN, AlGaN or GaN epitaxy.
  • At least the top layer of the polycrystalline 2D material interposer is composed of two crystalline domains whose orientations are matched at an angle of 60 degrees to each other.
  • the present invention cuts a high-quality single-crystal c-plane (c-plane) sapphire lamination thin layer and then joins it on the surface of a polycrystalline AlN substrate, which can directly grow layers with good crystallinity and there are two types (0 ° and 60°) polycrystalline oriented 2D material interposer, which avoids the transfer process and possible quality influence; the formation of a substrate whose surface lattice constant is highly matched with AlN, AlGaN and GaN can effectively overcome the Heteroepitaxial lattice mismatch causes defect quality problems in gallium nitride layers; the characteristics of van der Waals junctions can alleviate some of the thermal stress problems caused by different thermal expansion coefficients.
  • the substrate structure of the present invention is beneficial to be used for growing high-quality AlN, AlGaN and GaN epitaxial layers to manufacture GaN-based and other wide-energy-gap optoelectronic and semiconductor components.
  • FIG. 1 is a schematic diagram of a gallium nitride (GaN-on-Si) structure on a silicon wafer in the prior art
  • FIG. 2 is a schematic diagram of a gallium nitride on sapphire (GaN-on-Sapphire) structure in the prior art
  • Embodiment 1 of the present invention is a schematic structural diagram of Embodiment 1 of the present invention.
  • Embodiment 2 of the present invention is a schematic structural diagram of Embodiment 2 of the present invention.
  • Embodiment 3 of the present invention is a schematic structural diagram of Embodiment 3 of the present invention.
  • FIG. 6 is a schematic structural diagram of Embodiment 4 of the present invention.
  • FIG. 3 to FIG. 6 are embodiments of a gallium nitride epitaxial substrate with a 2D material interposer according to the present invention, including a polycrystalline AlN substrate 1 .
  • the polycrystalline AlN substrate 1 has a SiO 2 bonding layer 2 on it.
  • the SiO 2 bonding layer 2 has a c-plane sapphire bonding layer 3 .
  • the preferred design of the c-plane sapphire bonding layer 3 is that the thickness is greater than 10 nm.
  • a polycrystalline 2D material interposer is grown on the c-plane sapphire bonding layer 3 .
  • the 2D material interposer is a 2D layer suitable for GaN, AlGaN or AlN epitaxy.
  • the preferred design of the 2D material interposer is that the thickness is greater than 0.5 nm.
  • the polycrystalline 2D material interposer has at least one top layer 41, and the lattice constant of the top layer 41 is highly matched with AlN, AlGaN or GaN.
  • a GaN single-crystal epitaxial layer 5 is directly grown on the top layer 41 of the polycrystalline 2D material interposer by van der Waals epitaxy, or an AlN or AlGaN nucleation auxiliary layer is first grown on the top layer 41 of the polycrystalline 2D material interposer by van der Waals epitaxy. 6.
  • a GaN single crystal epitaxial layer 5 is formed on the AlN or AlGaN nucleation auxiliary layer 6 .
  • the 2D material interposer has a single-layer structure and only has a top layer 41 , and the top layer 41 is suitable for GaN, AlGaN or AlN epitaxy 2D material.
  • the GaN single crystal epitaxial layer 5 is directly grown on the top layer 41 by van der Waals epitaxy.
  • an AlN or AlGaN nucleation auxiliary layer 6 is first grown on the top layer 41 by van der Waals epitaxy, and then a GaN single crystal epitaxial layer 5 is formed on the AlN or AlGaN nucleation auxiliary layer 6 .
  • the 2D material interposer is a composite layer structure formed by a top layer 41 and a bottom layer 42 , and the top layer 41 is suitable for GaN, AlGaN or AlN epitaxy 2D material, the bottom layer 42 is a 2D material suitable as a single crystal base layer.
  • the GaN single crystal epitaxial layer 5 is directly grown on the top layer 41 by van der Waals epitaxy.
  • an AlN or AlGaN nucleation auxiliary layer 6 is first grown on the top layer 41 by van der Waals epitaxy, and then a GaN single crystal epitaxial layer 5 is formed on the AlN or AlGaN nucleation auxiliary layer 6 .
  • the top layer 41 of the present invention is a 2D layer that meets the requirements of lattice constant matching, such as WS 2 or MoS 2
  • the bottom layer 42 is a 2D layer suitable for the base layer, such as hBN, but not limited to the above materials.
  • the lattice constant a of the top layer 41 does not match AlN, AlGaN or GaN by more than 20% and is suitable for AlN, AlGaN or GaN epitaxy.
  • At least the top layer 41 of the polycrystalline 2D material interposer is composed of two crystalline domains with matching directions at an angle of 60 degrees.
  • step 1 the surface-polished polycrystalline AlN substrate 1 is used as the starting material, and the substrate surface is highly flattened by appropriate process treatment (including thin film evaporation, chemical mechanical polishing, spin-on-glass and heat treatment, etc.), as a follow-up procedure.
  • process treatment including thin film evaporation, chemical mechanical polishing, spin-on-glass and heat treatment, etc.
  • SiO 2 bonding layer 2 is coated on polycrystalline AlN substrate 1;
  • Step 2 using the existing process technology, transfer and bond the c-plane sapphire bonding layer 3 from the surface of the c-plane sapphire wafer to the SiO 2 bonding layer 2 on the surface of the aforementioned polycrystalline AlN substrate 1;
  • Step 3 using the existing manufacturing process, grow a polycrystalline 2D material interposer on the surface of the c-plane sapphire chip;
  • Step 4 using the van der Waals epitaxy technology, the subsequent GaN epitaxy can be continued on the polycrystalline AlN substrate 1 with the polycrystalline 2D material intermediary layer on the surface in Step 3; Epitaxy.
  • the present invention forms a substrate whose surface lattice constant is highly matched with AlN, AlGaN and GaN by directly growing polycrystalline 2D material heterojunction interlayer and van der Waals epitaxy (VDWE) on the surface of sapphire single crystal layer.
  • VDWE van der Waals epitaxy
  • the overall substrate structure of the invention and the heat dissipation performance of the components can maintain a good level, which is beneficial to the production of high-quality AlN, AlGaN and GaN epitaxial layers for the production of GaN-based and other wide-energy-gap optoelectronic and semiconductor components.

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Abstract

本发明公开了具有2D材料中介层的氮化镓外延基板，包含一多晶AlN基板；多晶AlN基板上有SiO 2接合层；SiO 2接合层上有c面蓝宝石贴合层；c面蓝宝石贴合层上成长多晶向2D材料中介层，多晶向2D材料中介层至少有一顶层，顶层晶格常数与AlN、AlGaN或GaN高度匹配；多晶向2D材料中介层上借助范德华外延生长GaN单晶外延层，或，借助范德华外延生长AlN或AlGaN成核辅助层，再在AlN或AlGaN成核辅助层上有GaN单晶外延层。本发明避免了2D材料中介层移转工序及可能的质量影响，有效克服异质外延晶格不匹配导致氮化镓层缺陷质量问题，可以缓解部分因热膨胀系数不同导致的热应力问题；有利于用来进行包含成长高质量AlN、AlGaN以及GaN外延层，以进行GaN系等宽能隙光电及半导体组件制作。

Description

具有2D材料中介层的氮化镓外延基板 技术领域
本发明涉及具有2D材料中介层的氮化镓外延基板。
背景技术
在光电及半导体的组件制造过程中，外延对产品的质量有重要的影响。其中对质量的影响包含组件效能、良品率、可靠度及寿命等。通常，基板的材料希望能尽量减少缺陷密度的单晶材料，在晶体结构、晶格常数(lattice constant)、热膨胀系数(CTE,coefficient of thermal expansion)与外延材料匹配才能尽可能避免在外延过程中影响晶体质量。近年第三代半导体技术与市场随功率、高频半导体组件需求快速发展，质量提升的基础，仰赖第三代半导体材料两个主角碳化硅与氮化镓高质量外延基板的供应。不同于氮化镓系LED采用蓝宝石基板为主，依照目前技术，最常采用的氮化镓基板是硅晶圆上氮化镓(GaN-on-Si)及碳化硅上氮化镓(GaN-on-SiC)两种基板。
主要原因来自氮化镓单晶技术发展目前成本与尺寸的限制。氮化铝和氮化镓的熔点均在摄氏两千五百度以上且存在蒸气压高问题，换言之，若想要直接以熔融长晶的方法制作前述两种材料的单晶基板，则不只制造成本更高，也相对会产生更多废热，对环境造成不可避免的污染。气相法长晶部分，目前氮化镓长晶采用的是氢化物气相外延法(Hydride Vapor Phase Epitaxy,HVPE)来生产单晶氮化镓基板，由于生产成本及产率条件等限制，目前量产技术达到4英寸基板同时成本极高。事实上，上述气相法缺陷密度仍然偏高于其他液相长晶工序，但受限于其余工序长晶速率过于缓慢，量产成本更为高昂，在市场需求、组件性能以及基板成本与供应量折衷考虑之下，商转主流仍限于HVPE法。文献指出气相法GaN长晶速率仍有提高数倍的可能并维持良好结晶性，但受限于缺陷密度劣化，目前并未能作为降低GaN 基板成本的取向。至于氮化铝长晶技术，采用的是气相法之一的物理气相传输法(Physical Vapor Transport,PVT)来生产单晶氮化铝基板，由于生产技术及良率限制，全球仅两家厂家有量产能力，目前量产技术仅达到2英寸基板同时成本极高，而产能全由少数厂商占有无法广泛供应市场。由于氮化铝本身化学特性以及物理气相传输法硬件零组件限制，单晶成品中一定程度的碳(C)与氧(O)杂质存在为不可避免，也一定程度影响组件特性。
表1
Figure PCTCN2021122990-appb-000001
类似的情形，也存在于目前碳化硅(SiC)单晶，碳化硅基板是目前高性能功率半导体以及高端发光二极管的基板材料，单晶长晶工序为气相法中的物理气相传输法(Physical Vapor Transport,PVT)，高质量大尺寸碳化硅单晶成长技术难度高，高端量产技术掌握在少数厂商手中，影响所及应用成本仍有很大进步空间。碳化硅上氮化镓(GaN-on-SiC)为高质量的氮化镓外延基板，但综合以上原因，大尺寸基板存在价格高昂、供应量有限及技术掌握在少数厂商手中等问题；相对而言，硅基板尺寸大、成本低、产能高且质量稳定，硅晶圆上氮 化镓(GaN-on-Si)基板发展更普遍为相关厂商关注。
硅晶圆上氮化镓(GaN-on-Si)及碳化硅上氮化镓(GaN-on-SiC)两种基板技术，在外延制程方面皆属异质接面外延技术，异质外延需克服不同材质之间的晶格匹配问题，以及外延层和基板间因热膨胀系数不同导致的热应力问题，GaN-on-SiC比GaN-on-Si质量高正是因为GaN-on-SiC晶格不匹配(lattice mismatch)的程度较GaN-on-Si小；另一个重要特性是氮化镓层在硅表面存在显著的张应力，当提升氮化镓层厚度时应力更高，导致基板的弯曲形变甚至氮化镓层可能开裂，随着晶圆尺寸增大时相关效应也更加严重。相关技术困难导致GaN-on-Si的良品率普遍较低，且多应用于电力电源产品，目前量产仍以六吋为主，硅晶圆大尺寸的优势未能完全发挥。
二维材料(two-dimensional(2D)materials)是一个快速发展的新兴领域，2D材料家族中最早吸引大量研发投入也最知名的材料为石墨烯(graphene),其二维层状结构具备特殊或优异的物理/化学/机械/光电特性，层与层间则没有强力的键结存在，仅以范德华力结合,这也表示层状结构表面没有空悬键(dangling bond)存在，目前石墨烯已被确认具有广泛而优异的应用潜能；石墨烯研发工作于全球普遍开展,同时也带动更多2D材料的研发，包括六方氮化硼hBN(hexagonal Boron Nitride)、过渡金属二硫族化物TMDs(transition metal dichalcogenides)以及黑磷black phosphorus等也是2D材料家族中累积较多研发成果者，上述材料均各自具备特异的材料特性与应用潜能,相关材料的制造技术开发也持续积极推展中。除了优异的光电特性之外,石墨烯、hBN以及TMDs材料之一的MoS 2都被视为具有优异的扩散阻障特性，也有程度不一的高温稳定性，尤其hBN更具有绝佳的化学钝性(inertness)以及高温耐氧化性。
由于具备上述层状结构本质以及层间范德华力结合特性，将2D材料家族中两种或多种材料制作成层状堆栈异质结构(hetero-structures)技术可行性大开，异质结构除了结合不同特性更创造出新的应用特性或制作出新的组件成为可能，目前光电及半导体领域的研发相当积极。具体可以是机械性组成迭层，也可以是物理或化学气相沉积。
2D材料的范德华力结合特性也获得应用于传统3D材料的外延基 板用途的关注，其着眼点在于外延技术中外延材料在晶体结构、晶格常数(lattice constant)、热膨胀系数(CTE,coefficient of thermal expansion)必须与基板材料匹配非常良好，但现实上常遭遇如本发明主题欠缺适合基板材料，或者是理想的基板材料成本偏高或不容易取得等情形，此时2D材料对于异质外延基板提供了另一种解决方案，也就是所谓的范德华外延(van der Waals Epitaxy)。范德华外延可能有利于异质外延的机制来自于传统外延界面直接的化学键改由范德华力结合所取代，将使得来自于外延工序中晶格以及热膨胀不匹配的应力或应变能因此获得一定程度的舒缓，从而使得外延层质量获得改善，或者说通过2D材料以及范德华外延导入可以使某些原先无法实用化的异质外延技术成为可能。相关研究也指出，当上述2D材料相互迭层异质结构时，相互间作用力以范德华力为主；而在2D材料上进行3D材料的外延时，由于界面上3D材料的空悬键(dangling bond)存在同时对接口的结合力有贡献，这种外延实质上并非纯粹范德华外延(van der Waals Epitaxy)或者更精确地可视为准范德华外延(Quasi van der Waals Epitaxy)；不论何种情形，晶格与热膨胀的匹配程度，无疑地仍对最终的外延质量起了一定的作用，2D材料中介层与基板材料都对整体的匹配度有所贡献。上述2D层状材料具有六角形或蜂巢状(hexagon or honeycomb)结构，与纤锌矿(Wurtzite)和闪锌矿(Zinc-Blende)结构材料在外延时被视为结构兼容，本发明相关领域主要外延材料均属此类结构。
基于外延基板用途，单晶(single crystal)为确保磊晶质量的要求之一，一般2D材料成长往往会在成核阶段与结晶性基板晶体指向呈现相关性，当基板采用一般金属箔片时由于属于多晶结构，2D材料在成核阶段已经形成方向不一致，晶核随成长聚合成连续薄膜后仍存在不同指向的区块(domain)而非单晶；当基板采用单晶材料如蓝宝石，仍然因为两者结构对称相关性导致可能出现的特定成核指向并非唯一，而无法形成单晶连续薄膜。近期的研究发现通过改进既存工艺，将铜箔经过热处理形成特定晶格指向的铜箔时，可以消弭2D材料石墨烯和六方氮化硼(hBN)成长过程形成的异向晶格区块(domain)特征，而长成单晶石墨烯和六方氮化硼连续薄膜。
近年研究指出在单晶的c面(c-plane)蓝宝石表面可以CVD等方 式成长结晶性良好的层状MoS 2、WS 2、MoSe 2、WSe 2等TMD材料，成长出来的TMD材料存在两种(0°及60°)晶体指向(crystal orientation)(参考文献：Nature 2019,v.567,169-170)。针对本发明所关注的AlGaN以及GaN材料而言，晶体结构在外延接面上具有六方对称性，上述的TMD层虽不构成单晶层，但理论上作为外延基板时无碍于AlGaN以及GaN外延层形成单晶。目前在蓝宝石以外基板表面应用时，常采用在高质量蓝宝石表面成长的二维材料层经过移转工序移转到其他基板表面；在高质量蓝宝石表面成长二维材料层不经过移转而直接应用时，理论上可以避免二维材料层由移转工序而来的包含缺陷、皱褶及表面污染物残留等可能质量影响。
现有工艺的硅晶圆上氮化镓(GaN-on-Si)，如图1所示。异质外延需克服不同材质之间的晶格匹配问题，以及外延层和基板间因热膨胀系数不同导致的热应力问题，GaN-on-Si晶格不匹配(lattice mismatch)的程度较高，导致外延过程中氮化镓层缺陷密度偏高；另一个重要特性是氮化镓层在硅表面存在显著的张应力，当提升氮化镓层厚度时应力更高，导致基板的弯曲形变甚至氮化镓层可能开裂，随着晶圆尺寸增大时相关效应也更加严重。相关技术困难导致GaN-on-Si的良品率普遍较低，且多应用于电力电源产品，目前量产仍以六吋为主，硅晶圆大尺寸的优势未能完全发挥。
现有工艺的蓝宝石上氮化镓(GaN-on-Sapphire)，如图2所示。异质外延需克服不同材质之间的晶格匹配问题，以及外延层和基板间因热膨胀系数不同导致的热应力问题，GaN-on-Sapphire晶格不匹配(lattice mismatch)的程度高，导致外延过程中氮化镓层缺陷密度呈一定水平,在发光二极管长期商业技术开发下,仍存在不可替代的地位；但是在高频与功率半导体领域，由于蓝宝石热传导系数偏低导致蓝宝石上氮化镓(GaN-on-Sapphire)的应用受阻。
发明内容
为了解决现有工艺中存在的问题，本发明提供一种具有2D材料中介层的氮化镓外延基板。
本发明的解决方案如下：
具有2D材料中介层的氮化镓外延基板，包含一多晶AlN基板； 多晶AlN基板上有SiO 2接合层；SiO 2接合层上有c面蓝宝石贴合层；c面蓝宝石贴合层上成长多晶向2D材料中介层，多晶向2D材料中介层至少具有一顶层，顶层晶格常数与AlN、AlGaN或GaN高度匹配；多晶向2D材料中介层上借助范德华外延生长有GaN单晶外延层，或者，多晶向2D材料中介层上借助范德华外延生长有AlN或AlGaN成核辅助层，再在AlN或AlGaN成核辅助层上有GaN单晶外延层。
所述2D材料中介层的厚度大于0.5nm。
所述c面蓝宝石贴合层的厚度大于10nm。
所述2D材料中介层为适用于GaN、AlGaN或AlN外延的2D层。
所述2D材料中介层为单层结构，只具有顶层，顶层为适用于GaN、AlGaN或AlN外延的2D材料。
所述2D材料中介层为由顶层和底层形成的复合层结构，顶层为适用于GaN、AlGaN或AlN外延的2D材料，底层为适合作为单晶基层的2D材料。
所述顶层采用WS 2或MoS 2；底层采用hBN。
所述2D材料中介层的单层结构或者复合层结构的顶层晶格常数a与AlN、AlGaN或GaN不匹配度不大于20％且适用于AlN、AlGaN或GaN外延。
所述多晶向2D材料中介层至少顶层是由两种互呈60度角度匹配方向的结晶区域(domain)所组成。
采用上述方案后，本发明将高质量单晶的c面(c-plane)蓝宝石贴合薄层切割后接合在多晶AlN基板表面，可以直接成长结晶性良好的层状并存在两种(0°及60°)结晶区域(domain)指向的多晶向2D材料中介层，避免了移转工序及可能的质量影响；形成表层晶格常数与AlN、AlGaN以及GaN高度匹配的基板，可以有效克服异质外延晶格不匹配导致氮化镓层缺陷质量问题；范德华接面的特性可以缓解部分因热膨胀系数不同导致的热应力问题。由于仅采用蓝宝石贴合层并接合主体为热传导性能优异的多晶AlN基板，整体基板架构与组件散热性能可以维系良好水平。因此本发明的基板结构有利于用来进行包含成长高质量AlN、AlGaN以及GaN外延层，以进行GaN系等宽能隙光电及半导体组件制作。
附图说明
图1是现有工艺的硅晶圆上氮化镓(GaN-on-Si)结构示意图；
图2是现有工艺的蓝宝石上氮化镓(GaN-on-Sapphire)结构示意图；
图3是本发明的实施例一结构示意图；
图4是本发明的实施例二结构示意图；
图5是本发明的实施例三结构示意图；
图6是本发明的实施例四结构示意图。
标号说明
多晶AlN基板1，SiO 2接合层2，蓝宝石贴合层3，2D材料中介层的顶层41和底层42，GaN单晶外延层5，AlN或AlGaN成核辅助层6。
具体实施方式
下面结合附图和具体实施例对本发明作进一步详细说明。
请参阅图3至图6，是本发明具有2D材料中介层的氮化镓外延基板的实施例，包含一多晶AlN基板1。多晶AlN基板1上有SiO 2接合层2。SiO 2接合层2上有c面蓝宝石贴合层3。所述c面蓝宝石贴合层3的较佳设计是厚度大于10nm。c面蓝宝石贴合层3上成长多晶向2D材料中介层。所述2D材料中介层为适用于GaN、AlGaN或AlN外延的2D层。所述2D材料中介层的较佳设计是厚度大于0.5nm。多晶向2D材料中介层至少具有一顶层41，顶层41晶格常数与AlN、AlGaN或GaN高度匹配。多晶向2D材料中介层的顶层41上直接借助范德华外延生长有GaN单晶外延层5，或者，多晶向2D材料中介层的顶层41上先借助范德华外延生长有AlN或AlGaN成核辅助层6，再在AlN或AlGaN成核辅助层6上有GaN单晶外延层5。
具体地，如图3所示的实施例一和如图5所示的实施例三，所述2D材料中介层为单层结构，只具有顶层41，顶层41为适用于GaN、AlGaN或AlN外延的2D材料。实施例一，顶层41上直接借助范德华外延生长有GaN单晶外延层5。实施例三，顶层41上先借助范德华外延生长有AlN或AlGaN成核辅助层6，再在AlN或AlGaN成核辅助层6上有GaN单晶外延层5。
如图4所示的实施例二和如图6所示的实施例四，所述2D材料中介层为由顶层41和底层42形成的复合层结构，顶层41为适用于GaN、AlGaN或AlN外延的2D材料，底层42为适合作为单晶基层的2D材料。实施例三，顶层41上直接借助范德华外延生长有GaN单晶外延层5。实施例四，顶层41上先借助范德华外延生长有AlN或AlGaN成核辅助层6，再在AlN或AlGaN成核辅助层6上有GaN单晶外延层5。
本发明所述顶层41为符合晶格常数匹配等需求的2D层，如采用WS 2或MoS 2，底层42为适合作为基层的2D层，如采用hBN，但不限于上述材料。
表2
材料 晶格常数a(nm)
六方氮化硼hBN 0.25
石墨烯graphene 0.246
WS 2 0.318
MoS 2 0.3161
WSe 2 0.3297
MoSe 2 0.3283
所述2D材料中介层不论单层结构还是复合层结构，顶层41晶格常数a与AlN、AlGaN或GaN不匹配度不大于20％且适用于AlN、AlGaN或GaN外延。所述多晶向2D材料中介层至少顶层41是由两种互呈60度角度匹配方向的结晶区域(domain)所组成。
本发明具有2D材料中介层的硅上氮化镓GaN-on-Si外延基板的制备方法，步骤如下：
步骤1，以表面抛光的多晶AlN基板1为起始材料，经由适当制程处理(含薄膜蒸镀,化学机械研磨,spin-on-glass及热处理等)使基板表面达高度平坦化，作为后续制造程序的准备；SiO 2接合层2披覆在多晶AlN基板1上；
步骤2，以既有制程技术，将c面蓝宝石贴合层3自c面蓝宝石 晶圆表面移转接合至前述多晶AlN基板1表面的SiO 2接合层2上；
步骤3，以既有制造工艺，在c面蓝宝石芯片表面成长多晶向2D材料中介层；
步骤4，利用范德华外延技术，在步骤3中表面具有多晶向2D材料中介层的多晶AlN基板1上可继续进行后续GaN外延；或先进行AlN或AlGaN成核层披覆再继续进行GaN外延。
本发明借助蓝宝石单晶层表面直接成长多晶向2D材料异质接合中介层与范德华外延(VDWE)之应用，形成表层晶格常数与AlN、AlGaN以及GaN高度匹配的基板。本发明有效克服了异质外延晶格不匹配导致氮化镓层缺陷质量问题；缓解因热膨胀系数不同导致的热应力问题。本发明整体基板架构与组件散热性能可以维系良好水平，有利于用来进行包含成长高质量AlN、AlGaN以及GaN外延层，以进行GaN系等宽能隙光电及半导体组件制作。
以上所述仅为本发明的较佳实施例，并非对本发明的限制。应当指出，本领域的技术人员在阅读完本说明书后，依本案的设计思路所做的等同变化，均落入本案的保护范围。

Claims (10)

  1. 具有2D材料中介层的氮化镓外延基板，其特征在于：包含一多晶AlN基板；多晶AlN基板上有SiO 2接合层；SiO 2接合层上有c面蓝宝石贴合层；c面蓝宝石贴合层上成长多晶向2D材料中介层，多晶向2D材料中介层至少具有一顶层，顶层晶格常数与AlN、AlGaN或GaN高度匹配；多晶向2D材料中介层上借助范德华外延生长有GaN单晶外延层，或者，多晶向2D材料中介层上借助范德华外延生长有AlN或AlGaN成核辅助层，再在AlN或AlGaN成核辅助层上有GaN单晶外延层。
  2. 如权利要求1所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述2D材料中介层的厚度大于0.5nm。
  3. 如权利要求1所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述c面蓝宝石贴合层的厚度大于10nm。
  4. 如权利要求1所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述2D材料中介层为适用于GaN、AlGaN或AlN外延的2D层。
  5. 如权利要求1所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述2D材料中介层为单层结构，只具有顶层，顶层为适用于GaN、AlGaN或AlN外延的2D材料。
  6. 如权利要求5所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述顶层采用WS 2或MoS 2。
  7. 如权利要求1所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述2D材料中介层为由顶层和底层形成的复合层结构，顶层为适用于GaN、AlGaN或AlN外延的2D材料，底层为适合作为单晶基层的2D材料。
  8. 如权利要求7所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述顶层采用WS 2或MoS 2；底层采用hBN。
  9. 如权利要求1至8中任一项所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述2D材料中介层的单层结构或者复合层结构的顶层晶格常数a与AlN、AlGaN或GaN不匹配度不大于20％ 且适用于AlN、AlGaN或GaN外延。
  10. 如权利要求1至8中任一项所述的具有2D材料中介层的氮化镓外延基板，其特征在于：所述多晶向2D材料中介层至少顶层是由两种互呈60度角度匹配方向的结晶区域所组成。
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