Large-area polycrystalline diamond GaN heterostructure with slowly-changing Sc component transition layer and preparation method of large-area polycrystalline diamond GaN heterostructure

Abstract

The invention provides a large-area polycrystalline diamond GaN heterostructure with a slowly-changing Sc component transition layer and a preparation method of the large-area polycrystalline diamond GaN heterostructure. The preparation method comprises the steps that polycrystalline diamond is pretreated, and a polycrystalline diamond substrate is obtained; performing etching mask deposition and patterning on the polycrystalline diamond substrate, and forming a plurality of nano columnar structures in the upper region of the polycrystalline diamond substrate; carrying out magnetron sputtering on a first ScAlN transition layer with 35% of Sc component at the nano columnar structure; epitaxially growing a second ScAlN transition layer with 30% of Sc component on the first transition layer; epitaxially growing a third ScAlN transition layer with 20% of Sc component on the second transition layer; epitaxially growing a fourth ScAlN transition layer with 10% of Sc component on the third transition layer; and epitaxially growing a GaN epitaxial layer on the fourth transition layer. According to the method, the magnetron sputtering technology and the epitaxial ScAlN technology are combined, the respective advantages are exerted, the large-area and high-quality diamond-based GaN silbby batch is prepared, and good conductivity, high thermal stability and high reliability are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor devices, in particular to a large-area polycrystalline diamond GaN heterostructure with a transition layer of a gradually changing Sc component and a preparation method thereof. BACKGROUND

[0002] In the field of semiconductor devices, the research on heteroepitaxy of high-quality GaN on large-area polycrystalline diamond is a significant topic. Using large-area polycrystalline diamond as a GaN epitaxial growth substrate can significantly reduce costs and enable large-area preparation, laying the foundation for the industrialization of GaN devices.

[0003] However, in the prior art, the use of large-area polycrystalline diamond as a GaN epitaxial growth substrate has the following defects: 1. There is a large lattice mismatch and a difference in thermal expansion coefficient between polycrystalline diamond and GaN material, resulting in a high defect density of the epitaxially grown GaN material, which affects device performance. Reducing lattice mismatch is the key to achieving high-quality GaN / diamond heteroepitaxy. 2. The grinding and polishing process of large-area polycrystalline diamond is difficult, making it difficult to prepare a diamond substrate with low defect density and low roughness. The rough surface of the polycrystalline diamond increases the difficulty of epitaxial growth.

[0004] ScAlN has a lattice constant between polycrystalline diamond and GaN, and is compatible with GaN epitaxy process, making it a feasible transition layer material for polycrystalline diamond / GaN epitaxy to reduce lattice mismatch.

[0005] Currently, the ScAlN thin film is mainly grown by molecular beam epitaxy and reactive magnetron sputtering in the prior art. Molecular beam epitaxy technology has excellent ScAlN film quality and structural integrity, but has the defects of high equipment investment and operating cost, slow growth rate, and difficulty in achieving large-area uniform growth. Magnetron sputtering technology has the advantages of low cost, fast growth rate, and the ability to achieve large-area uniform growth, but has the defects of poor film quality and structural integrity, and poor component control precision.

[0006] In view of the above problems in the heteroepitaxial growth of large-size polycrystalline diamond-based GaN, the present application provides a new large-area polycrystalline diamond GaN heterostructure with a transition layer of a gradually changing Sc component and a preparation method thereof. SUMMARY

[0007] Based on the above description, the application provides a large-area polycrystalline diamond GaN heterostructure with a transition layer with a slowly-varying Sc component and a preparation method thereof, to solve the problems of lattice mismatch, slow growth rate, poor quality and structural integrity, and poor component control accuracy in the heteroepitaxial growth of large-size polycrystalline diamond-based GaN in the prior art.

[0008] The technical solution of the application for solving the above technical problems is as follows: In a first aspect, the application provides a large-area polycrystalline diamond GaN heterostructure with a transition layer with a slowly-varying Sc component, comprising the following steps: S1: pretreating polycrystalline diamond to obtain a polycrystalline diamond substrate; S2: performing etching mask deposition and patterning on the polycrystalline diamond substrate to form a plurality of nano-pillar structures in the upper region of the polycrystalline diamond substrate; S3: magnetron sputtering a first ScAlN transition layer with a Sc component of 35% at the nano-pillar structures; S4: epitaxially growing a second ScAlN transition layer with a Sc component of 30% on the first transition layer; S5: epitaxially growing a third ScAlN transition layer with a Sc component of 20% on the second transition layer; S6: epitaxially growing a fourth ScAlN transition layer with a Sc component of 10% on the third transition layer; S7: epitaxially growing a GaN epitaxial layer on the fourth transition layer.

[0009] On the basis of the above technical solution, the application can also be improved as follows.

[0010] Further, step S1 specifically comprises: Step S101: selecting a 4-6 inch large-area polycrystalline diamond as a heat dissipation substrate, and performing coarse grinding using a diamond grinding wheel with a larger particle size, so that the surface roughness of the substrate is less than 20 nm; Step S102: performing fine grinding on the surface of the coarsely ground polycrystalline diamond using a diamond grinding wheel with a smaller particle size, so that the surface roughness of the substrate is less than 5 nm; Step S103: performing polishing treatment on the finely ground substrate by a chemical mechanical polishing method, so that the surface roughness of the substrate reaches 0.5 nm, to obtain a large-area polycrystalline diamond substrate.

[0011] Further, step S2 specifically comprises: Step S201: coating photoresist on the polycrystalline diamond substrate, and performing photolithography and development to uncover the diamond micro-pillar region to be etched; Step S202: magnetron sputtering Ni metal and stripping off the definition of the etched diamond micro-pillar pattern; Step S203: performing patterned etching on the polycrystalline diamond substrate to an etching depth of 180-220 nm; Step S203: using an inorganic solution to clean and remove the Ni mask on the surface, thereby completing the patterning of the columnar structure.

[0012] Furthermore, step S3 specifically includes: Step S301: transferring the polycrystalline diamond substrate having a micro-pillar structure on its surface into a magnetron sputtering device; Step S302: Using a source of 15.24 cm Sc 0.43 Al 0.57 The alloy target material is used to sputter the polycrystalline diamond substrate with ScAlN; a Sc alloy with a thickness of 1000 nm and a Sc component of 35% is obtained. 0.35 Al 0.65 N transition layer.

[0013] Furthermore, step S4 specifically includes: Step S401: Sc 0.35 Al 0.65 The ScAlN diamond with N transition layer is loaded onto the molybdenum support of the molecular beam epitaxy equipment; Step S402: slowly raising the temperature to the ScAlN growth temperature, controlling the flow rates of Sc, Al, and N precursor gases through mass flow controllers, and introducing the reaction gases into the vacuum chamber through injection tubes while monitoring the reaction pressure and temperature; Step S403: By adjusting the flow ratio of Sc, Al and N precursor gases, controlling the Sc component at 30%, adjusting the growth rate to 0.1-1.0 μm / h, a Sc film with a thickness of 200 nm and a Sc component of 30% is obtained. 0.3 Al 0.7 N transition layer.

[0014] Furthermore, step S5 specifically includes: Adjust the flow ratio of Sc, Al and N precursor gases, and use molecular beam epitaxy equipment to produce Sc 0.3 Al 0.7 The ScAlN diamond of the N transition layer was further epitaxially treated to control the Sc content at 20%, and a ScAlN diamond with a thickness of 50nm and a Sc content of 20% was obtained. 0.2 Al 0.8 N transition layer.

[0015] Furthermore, step S6 specifically includes: Adjust the flow ratio of Sc, Al and N precursor gases, and use molecular beam epitaxy equipment to produce Sc0.2 Al 0.8 ScAlN diamond of the N transition layer is subjected to further epitaxial treatment, and the Sc component is controlled to be 10%, thereby obtaining a ScAlN diamond with a thickness of 20 nm and a Sc component of 10% 0.1 Al 0.9 N transition layer.

[0016] Further, the step S7 specifically comprises: The Sc 0.2 Al 0.8 N transition layer is grown by a molecular beam epitaxy device to form a GaN epitaxial layer with a thickness of 400 nm.

[0017] In a second aspect, the present application further provides a large-area polycrystalline diamond GaN heterostructure with a transition layer with a gradually changing Sc component, which is prepared by the method of the first aspect, and comprises, from bottom to top, a polycrystalline diamond substrate, a first ScAlN transition layer, a second ScAlN transition layer, a third ScAlN transition layer, a fourth ScAlN transition layer and a GaN epitaxial layer. The upper region of the polycrystalline diamond substrate is formed with a plurality of nano-pillar structures.

[0018] On the basis of the above technical solution, the present application can be further improved as follows.

[0019] Further, the first ScAlN transition layer is a Sc 0.35 Al 0.65 N transition layer. The second ScAlN transition layer is a Sc 0.3 Al 0.7 N transition layer. The third ScAlN transition layer is a Sc 0.2 Al 0.8 N transition layer. The fourth ScAlN transition layer is a Sc 0.1 Al 0.9 N transition layer Compared with the prior art, the technical solution of the present application has the following beneficial technical effects: The application provides a preparation method of a large-area polycrystalline diamond GaN heterostructure with a slowly-varying Sc component transition layer.

[0020] Compared with the prior art, the following beneficial effects are achieved: (1) Low cost: The method of preparing GaN by heteroepitaxy on a large-area polycrystalline diamond substrate through a ScAlN transition layer is simpler and has lower cost than the methods of preparing diamond-based GaN by laser stripping and secondary bonding or Y metal as a transition layer. In addition, the method of preparing thick-film ScAlN by magnetron sputtering on a large-area polycrystalline diamond substrate has lower cost than the traditional epitaxial growth methods such as molecular beam epitaxy and metal organic chemical vapor deposition. (2) Low thermal resistance: ScAlN is an ideal transition layer material that can effectively alleviate the lattice mismatch between diamond and GaN, and has good thermal stability and chemical inertness. By optimizing the growth conditions and structure design of the ScAlN transition layer, a high-quality GaN epitaxial layer is obtained on the diamond substrate, thereby promoting the development of GaN-based power electronic and optoelectronic devices.

[0021] (3) Low mismatch stress: The diamond lattice constant is adjusted by using a diamond microcolumn process, and the ScAlN lattice constant is adjusted by combining multi-layer ScAlN slow growth, thereby effectively reducing the lattice mismatch between diamond and magnetron sputtered ScAlN, between magnetron sputtered ScAlN and molecular beam epitaxy ScAlN, in the molecular beam epitaxy of ScAlN, and between ScAlN and GaN materials, reducing the material growth stress, and obtaining high-quality diamond-based gallium nitride materials.

[0022] In general, the two different ScAlN preparation processes of magnetron sputtering ScAlN and MBE epitaxy ScAlN are combined to give full play to the advantages of each process, and large-area, high-quality diamond-based GaN materials are prepared, which not only have good conductivity, but also have high thermal stability and high reliability, and can meet the needs of the development of modern electronic equipment towards high frequency, high speed and high power. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A manufacturing process schematic diagram of a large-area polycrystalline diamond GaN heterostructure with a transition layer having a gradually changing Sc component is provided for Embodiment 1 of the present application; Figure 2 A structure schematic diagram of a large-area polycrystalline diamond GaN heterostructure with a transition layer having a gradually changing Sc component is provided for Embodiment 2 of the present application; In the drawings, the components represented by each reference numeral are listed as follows: 1, polycrystalline diamond substrate; 2, nano-pillar structure; 3, first ScAlN transition layer; 4, second ScAlN transition layer; 5, third ScAlN transition layer; 6, fourth ScAlN transition layer; 7, GaN epitaxial layer. DETAILED DESCRIPTION

[0024] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the related drawings. The embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0025] The ScAlN lattice constant is between polycrystalline diamond and GaN, and is compatible with GaN epitaxy process, which is a feasible polycrystalline diamond / GaN epitaxial transition layer material.

[0026] In the prior art, such as Patent No. CN113193040A - AlN / GaN / ScAlN / GaN double-channel heterojunction on diamond substrate and preparation method, the structure includes from bottom to top:

[111] crystal direction diamond substrate layer; low-temperature GaN nucleation layer; high-temperature GaN nucleation layer; GaN bottom channel layer; ScAlN barrier layer; GaN top channel layer; AlN barrier layer; GaN cap layer. Although the ScAlN barrier layer is mentioned, this technology is to directly epitaxial GaN nucleation layer on diamond, which lacks a transition layer, and the lattice constant difference between GaN and diamond is large, resulting in serious lattice mismatch; ScAlN is only used as a heterojunction material for GaN, and does not play the advantages of high thermal conductivity and lattice matching with diamond.

[0027] Currently, molecular beam epitaxy (MBE) and reactive magnetron sputtering (RMS) are the two main methods for growing ScAlN thin films. MBE utilizes thermal evaporation or ion beam sputtering of atomic sources in an ultra-high vacuum environment to achieve controlled growth of single atomic or molecular layers on a heated substrate surface. This allows for precise control of the composition, thickness, and doping concentration of the ScAlN film. This method achieves excellent ScAlN film quality and structural integrity, but it comes with high equipment investment and operating costs, slow growth rates, and difficulty achieving uniform growth over large areas.

[0028] In contrast, magnetron sputtering technology uses plasma to sputter target atoms under relatively low vacuum conditions and forms the desired ScAlN thin film material with the reaction gas. It has the advantages of low cost, fast growth rate, and the ability to achieve uniform growth over a large area. However, its film quality and structural integrity are poor, and the composition control accuracy is not as good as MBE. In general, MBE and magnetron sputtering have their own advantages and disadvantages in preparing ScAlN, and a trade-off needs to be made in different application scenarios. For devices with extremely high film quality requirements, MBE ScAlN is the preferred option; for large-area growth and low-cost applications, magnetron sputtering ScAlN is more advantageous.

[0029] This paper proposes a large-area polycrystalline diamond / magnetron sputtered ScAlN / MBE ScAlN / GaN heterostructure and preparation method, which can simultaneously meet the extremely high requirements of film quality and large-area growth and low-cost application.

[0030] The embodiments of the present invention are described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0031] It should be noted that the terms "first", "second", "third" and "fourth" in the description, claims and drawings of this application are used to distinguish different objects rather than to limit a specific order.

[0032] The abbreviations and key terms in this patent are defined as follows: ScAlN: scandium aluminum nitride; GaN: Gallium Nitrogen; Polycrystalline diamond: polycrystalline diamond; MBE: molecular beam epitaxy; Sputter: Magnetron sputtering.

[0033] Example 1 like Figure 1 As shown, this embodiment provides a method for preparing a large-area polycrystalline diamond GaN heterostructure with a graded Sc composition transition layer, comprising the following steps: S1: Pre-treating polycrystalline diamond to obtain a polycrystalline diamond substrate.

[0034] Specifically, the step includes: Step S101: Selecting a 4-6 inch large-area polycrystalline diamond as a heat dissipation substrate, and using a diamond grinding wheel with a larger particle size for rough grinding to make the surface roughness of the substrate less than 20 nm.

[0035] Among them, the 4-6 inch polycrystalline diamond is used as the heat dissipation substrate, and the diamond has excellent thermal conductivity and low thermal expansion coefficient, which can effectively improve the thermal stability of the device.

[0036] Step S102: Using a diamond grinding wheel with a smaller particle size to finely grind the surface of the rough-ground polycrystalline diamond to make the surface roughness of the substrate less than 5 nm.

[0037] Step S103: Polishing the finely ground substrate by chemical mechanical polishing to make the surface roughness of the substrate reach 0.5 nm, and obtaining a large-area polycrystalline diamond substrate.

[0038] In one specific example, the polycrystalline diamond substrate is rough-ground, a diamond grinding wheel with a larger particle size (100-200 mesh) is used to rough-ground the surface of the polycrystalline diamond at a speed of about 2000-3000 rpm, to remove surface defects and larger unevenness, and make the roughness less than 20 nm.

[0039] Then, a diamond grinding wheel with a smaller particle size (400-800 mesh) is used to finely grind the surface of the polycrystalline diamond at a speed of about 3000-5000 rpm, to make the roughness less than 5 nm.

[0040] Finally, a chemical mechanical polishing slurry containing diamond particles, an oxidizing agent and a stabilizer is prepared by chemical mechanical polishing to further reduce the surface roughness of the polycrystalline diamond, and finally make the roughness of the polycrystalline diamond reach 0.5 nm.

[0041] S2: Etching mask deposition and patterning on the polycrystalline diamond substrate to form a plurality of nano-pillar structures in the upper region of the polycrystalline diamond substrate.

[0042] Specifically, the step includes: Step S201: Coating photoresist on the polycrystalline diamond substrate, and using photoetching and development to mask the diamond micro-pillar area to be etched.

[0043] Step S202: Magnetron sputtering of Ni metal, and stripping the definition of the etched diamond micro-pillar pattern.

[0044] Step S203: performing patterned etching on the polycrystalline diamond substrate, and the etching depth is 180-220 nm.

[0045] Step S203: removing the surface Ni mask by inorganic solution cleaning to complete the patterning of the columnar structure.

[0046] It should be noted that the patterned etching by the ICP device retains a plurality of island-shaped microcolumns on the polycrystalline diamond surface, and the lattice mismatch of heteroepitaxy can be effectively reduced by means such as reducing the lattice constant, releasing stress, and interface engineering, thereby improving the crystal quality and performance of the ScAlN layer.

[0047] In a specific example, first, photoresist is coated on the diamond substrate, then photolithography and development are performed to mask out the diamond microcolumn region to be etched, Ni metal is magnetron sputtered, and the definition of the etched diamond microcolumn pattern is stripped, and the length and width of the microcolumn pattern are about 100x100 μm. Alternatively, the etching mask layer can also be Si3N4, SiO2, or other dielectric or W, Cr, and the like.

[0048] Then, the diamond is patterned etched by using the ICP device, the oxygen flow is 200 sccm, the direct current power is 1000 W, the alternating current power is 150 W, the etching time is 30 min, and the diamond etching depth is about 200 nm.

[0049] Finally, the surface Ni mask is removed by inorganic solution cleaning to complete the patterning of the diamond microcolumn.

[0050] S3: magnetron sputtering of a first ScAlN transition layer with a Sc component of 35% at the nanocolumnar structure.

[0051] Specifically, the step includes: Step S301: transferring the polycrystalline diamond substrate with a microcolumn structure on the surface into a magnetron sputtering device.

[0052] Step S302: using a 15.24 cm Sc 0.43 Al 0.57 alloy target as the source to perform ScAlN magnetron sputtering on the polycrystalline diamond substrate; and obtaining a Sc 0.35 Al 0.65 N transition layer with a thickness of 1000 nm and a Sc component of 35%.

[0053] In a specific example, the diamond substrate with a microcolumn structure on the surface is sent to a magnetron sputtering device, and a 15.24 cm (6 inch) Sc 0.43 Al 0.57Alloy target. First, fix the gas flow at 22:2, then adjust the gas flow (N2:Ar, unit mL / min) to 24:10, 18:6, 15:3 and 22:2 under a sputtering power of 900 W, respectively, for 5 min, 10 min, 10 min and 20 min, respectively, to complete 1000 nm Sc 0.35 Al 0.65 N by magnetron sputtering. A thicker epitaxial thickness helps to release the stress between diamond and Sc 0.35 Al 0.65 N.

[0054] S4: epitaxially growing a second ScAlN transition layer with a Sc component of 30% on the first transition layer.

[0055] Specifically, the step includes: Step S401: loading ScAlN diamond with a Sc 0.35 Al 0.65 N transition layer onto a molybdenum holder of a molecular beam epitaxy device; Step S402: slowly warming up to the ScAlN growth temperature, controlling the precursor gas flow of Sc, Al and N through a mass flow controller, and introducing the reaction gas into the vacuum chamber through an injection tube, while monitoring the reaction pressure and temperature; Step S403: by adjusting the flow ratio of Sc, Al and N precursor gases, controlling the Sc component to be 30%, adjusting the growth rate to be 0.1-1.0 μm / h, and obtaining a Sc 0.3 Al 0.7 N transition layer with a thickness of 200 nm.

[0056] In one specific example, Sc 0.35 Al 0.65 N is loaded onto a specially customized molybdenum holder of an MBE device, slowly warmed up to the ScAlN growth temperature (700℃), the precursor gases of Sc, Al and N (Sc(Cp)2, Al(CH3)3, NH3) are precisely controlled in flow through a mass flow controller (MFC), and the reaction gas is introduced into the vacuum chamber through an injection tube, while the reaction pressure and temperature are monitored to ensure a stable growth environment.

[0057] By adjusting the flow ratio of Sc, Al and N, the Sc component is precisely controlled to be about 30%, and the growth rate is controlled within a suitable range (usually 0.1 to 1.0 μm / h) to obtain a high-quality epitaxial layer by molecular beam epitaxy (MBE), and the growth time is adjusted to control the epitaxial thickness of Sc 0.3 Al 0.7 N to be 200 nm.

[0058] S5: epitaxially growing a third ScAIN transition layer with Sc composition of 20% on the second transition layer.

[0059] Specifically, the step includes adjusting the flow ratio of Sc, Al and N precursor gases, and performing further epitaxial treatment on the ScAIN diamond with Sc 0.3 Al 0.7 N transition layer to control the Sc composition to be 20%, to obtain a Sc 0.2 Al 0.8 N transition layer with a thickness of 50 nm.

[0060] In a specific example, by adjusting the flow ratio of Sc, Al and N, the Sc composition is accurately controlled to be about 20%, the growth rate is controlled to be within a suitable range to obtain a high-quality epitaxial layer, the growth time is adjusted, and the epitaxial thickness of Sc 0.2 Al 0.8 N is controlled to be 50 nm.

[0061] S6: epitaxially growing a fourth ScAIN transition layer with Sc composition of 10% on the third transition layer.

[0062] Specifically, the step includes adjusting the flow ratio of Sc, Al and N precursor gases, and performing further epitaxial treatment on the ScAIN diamond with Sc 0.2 Al 0.8 N transition layer to control the Sc composition to be 10%, to obtain a Sc 0.1 Al 0.9 N transition layer with a thickness of 20 nm.

[0063] In a specific example, by adjusting the flow ratio of Sc, Al and N, the Sc composition is accurately controlled to be about 10%, the growth rate is controlled to be within a suitable range to obtain a high-quality epitaxial layer, the growth time is adjusted, and the epitaxial thickness of Sc 0.2 Al 0.8 N is controlled to be 20 nm.

[0064] In summary, the Sc 0.35 Al 0.65On the N transition layer, three layers of lattice-graded ScAlN with different Sc components are grown by MBE through pulse method, from bottom to top, the Sc components are 30%, 20% and 10% respectively; when the Sc component of ScAlN is between 10% and 30%, the physical and chemical properties are relatively stable; and when the Sc component of ScAlN increases from 10% to 30%, the c-axis lattice constant of ScAlN increases from 4.93 to 5.10 Å. By increasing the Sc component of ScAlN, the lattice mismatch between diamond and ScAlN can be reduced, and the heat dissipation efficiency and electrical conductivity of the material can be improved.

[0065] S7: epitaxially growing a GaN epitaxial layer on the fourth transition layer.

[0066] Specifically, the step comprises: growing the Sc 0.2 Al 0.8 N transition layer by a molecular beam epitaxy device.

[0067] In one specific example, a 400nm GaN epitaxial layer is grown on the transition layer by a molecular beam epitaxy method under the process conditions of a temperature of 670-720℃, a nitrogen flow rate of 2.3sccm, a gallium beam current equilibrium vapor pressure of 6.0x10 -7 -8.0x10 -7 Torr, and a nitrogen radio frequency source power of 375W, to complete the material preparation.

[0068] The Sc 0.1 Al 0.9 N surface of the uppermost layer is epitaxially grown with a GaN epitaxial layer, reducing the stress mismatch between ScAlN and GaN, and ensuring the quality and electrical properties of the GaN heterojunction material.

[0069] Embodiment 2 The embodiment provides a large-area polycrystalline diamond GaN heterostructure with a transition layer with a gradually changing Sc component, which is prepared by the preparation method provided in Embodiment 1, as shown in the following figure, and specifically comprises, from bottom to top, a polycrystalline diamond substrate 1, a first ScAlN transition layer 3, a second ScAlN transition layer 4, a third ScAlN transition layer 5, a fourth ScAlN transition layer 6 and a GaN epitaxial layer 7. Figure 2

[0070] Here, "a plurality of" means two or more.

[0071] Specifically, the first ScAlN transition layer 3 is a Sc 0.35 Al 0.65 N transition layer. The second ScAlN transition layer 4 is a Sc 0.3 Al​0.7 N transition layer; The third ScAlN transition layer 5 is Sc 0.2 Al 0.8 N transition layer; The fourth ScAlN transition layer 6 is Sc 0.1 Al 0.9 N transition layer.

[0072] In a specific example, the bottom layer is a large-area low-roughness polycrystalline diamond substrate with a size of 4-6 inches and a thickness of 375-1000 μm; the patterned diamond substrate in the upper region has multiple circular, hexagonal or square diamond micro-pillars with a thickness of about 10-200 nm.

[0073] On the substrate, from bottom to top, sequentially include: Sc 0.35 Al 0.65 N transition layer, forming a heterojunction with diamond, with a thickness of 1000 nm; Sc 0.3 Al 0.7 N transition layer, forming a heterojunction with Sc 0.35 Al 0.65 N, forming a gradual transition layer, with a thickness of 200 nm; Sc 0.2 Al 0.8 N transition layer, forming a heterojunction with Sc 0.3 Al 0.7 N, forming a gradual transition layer, with a thickness of 50 nm; Sc 0.1 Al 0.9 N transition layer, regulating the stress of ScAlN epitaxial growth, and serving as a heterojunction epitaxial growth layer for GaN, with a thickness of 20 nm; Epitaxial high-quality GaN epitaxial layer, with a thickness of about 400 nm.

[0074] In summary, the large-area polycrystalline diamond GaN heterostructure with a gradual Sc component transition layer provided by the above-mentioned embodiments 1 and 2 and the corresponding preparation method have the following technical effects: (1) Low cost: GaN prepared by heteroepitaxy on large-area polycrystalline diamond substrates with ScAlN as a transition layer is less expensive and simpler than methods such as laser liftoff followed by secondary bonding and Y metal as a transition layer for heteroepitaxy. In addition, thick-film ScAlN prepared by magnetron sputtering on large-area polycrystalline diamond substrates is less expensive than traditional epitaxial growth techniques such as molecular beam epitaxy and metal-organic chemical vapor deposition. (2) Low thermal resistance: ScAlN is an ideal transition layer material that not only effectively alleviates the lattice mismatch between diamond and GaN but also has good thermal stability and chemical inertness. By optimizing the growth conditions and structure design of the ScAlN transition layer, high-quality GaN epitaxial layers are obtained on diamond substrates, thereby promoting the development of GaN-based power electronic and optoelectronic devices.

[0075] (3) Low mismatch stress: Diamond microcolumn technology is used to control the lattice constant of diamond, and multi-layer ScAlN is used to control the lattice constant of ScAlN, effectively reducing the lattice mismatch between diamond and magnetron sputtered ScAlN, magnetron sputtered ScAlN and molecular beam epitaxy ScAlN, molecular beam epitaxy ScAlN, and ScAlN and GaN materials, reducing material growth stress, and obtaining high-quality diamond-based gallium nitride materials.

[0076] In summary, by surface treating diamond and magnetron sputtering thick-film ScAlN, the lattice mismatch between ScAlN and diamond is reduced, and the heterojunction heat dissipation efficiency is improved. By molecular beam epitaxy of Sc component gradient multi-layer ScAlN structure on magnetron sputtered ScAlN, the stress mismatch between ScAlN transition layers is reduced, and high-quality GaN buffer layer epitaxial growth is completed, thereby solving the problem of epitaxial growth of GaN materials on large-size polycrystalline diamond. That is, by combining magnetron sputtering ScAlN and MBE epitaxy ScAlN, the advantages of each process are fully utilized to prepare large-area, high-quality diamond-based GaN materials with good electrical conductivity, high thermal stability, and high reliability, which can meet the needs of modern electronic devices for high frequency, high speed, and high power.

[0077] In the description of the present specification, the description referring to the terms "specific example" or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In the present specification, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples, without contradiction.

[0078] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a large-area polycrystalline diamond GaN heterostructure with a graded Sc composition transition layer, characterized in that: The following steps are involved: S1: pre-treating the polycrystalline diamond to obtain a polycrystalline diamond substrate; S2: depositing and patterning an etching mask on the polycrystalline diamond substrate to form a plurality of nanocolumnar structures in an upper region of the polycrystalline diamond substrate; S3: magnetron sputtering a first ScAlN transition layer with a Sc content of 35% on the nano-columnar structure; S4: epitaxially growing a second ScAlN transition layer with a Sc content of 30% on the first transition layer; S5: epitaxially growing a third ScAlN transition layer having a Sc content of 20% on the second transition layer; S6: epitaxially growing a fourth ScAlN transition layer having a Sc content of 10% on the third transition layer; S7: epitaxially growing a GaN epitaxial layer on the fourth transition layer.

2. The preparation method according to claim 1, characterized in that Step S1 specifically includes: Step S101: Select a large-area polycrystalline diamond substrate of 4-6 inches as a heat dissipation substrate and use a diamond grinding wheel with a larger grain size to perform rough grinding to reduce the surface roughness of the substrate to less than 20 nm; Step S102: using a diamond grinding wheel with a smaller grit size to fine-grind the polycrystalline diamond surface after rough grinding, so that the surface roughness of the substrate is less than 5 nm; Step S103: polishing the finely ground substrate by chemical mechanical polishing to achieve a surface roughness of 0.5 nm, thereby obtaining a large-area polycrystalline diamond substrate.

3. The preparation method according to claim 1, characterized in that Step S2 specifically includes: Step S201: coating photoresist on the polycrystalline diamond substrate, and masking the diamond microcolumn area to be etched by photolithography and development; Step S202: magnetron sputtering Ni metal and stripping off the definition of the etched diamond micro-pillar pattern; Step S203: performing patterned etching on the polycrystalline diamond substrate to an etching depth of 180-220 nm; Step S203: using an inorganic solution to clean and remove the Ni mask on the surface, thereby completing the patterning of the columnar structure.

4. The preparation method according to claim 1, characterized in that Step S3 specifically includes: Step S301: transferring the polycrystalline diamond substrate having a micro-pillar structure on its surface into a magnetron sputtering device; Step S302: Using a source of 15.24 cm Sc 0.43 Al 0.57 The alloy target material is used to sputter the polycrystalline diamond substrate with ScAlN; a Sc alloy with a thickness of 1000 nm and a Sc component of 35% is obtained. 0.35 Al 0.65 N transition layer.

5. The preparation method according to claim 4, characterized in that Step S4 specifically includes: Step S401: Sc 0.35 Al 0.65 The ScAlN diamond with N transition layer is loaded onto the molybdenum support of the molecular beam epitaxy equipment; Step S402: slowly raising the temperature to the ScAlN growth temperature, controlling the flow rates of Sc, Al, and N precursor gases through mass flow controllers, and introducing the reaction gases into the vacuum chamber through injection tubes while monitoring the reaction pressure and temperature; Step S403: By adjusting the flow ratio of Sc, Al and N precursor gases, controlling the Sc component at 30%, adjusting the growth rate to 0.1-1.0 μm / h, a Sc film with a thickness of 200 nm and a Sc component of 30% is obtained. 0.3 Al 0.7 N transition layer.

6. The preparation method according to claim 5, characterized in that Step S5 specifically includes: Adjust the flow ratio of Sc, Al and N precursor gases, and use molecular beam epitaxy equipment to produce Sc 0.3 Al 0.7 The ScAlN diamond of the N transition layer was further epitaxially treated to control the Sc content at 20%, and a ScAlN diamond with a thickness of 50nm and a Sc content of 20% was obtained. 0.2 Al 0.8 N transition layer.

7. The preparation method according to claim 6, characterized in that Step S6 specifically includes: Adjust the flow ratio of Sc, Al and N precursor gases, and use molecular beam epitaxy equipment to produce Sc 0.2 Al 0.8 The ScAlN diamond of the N transition layer was further epitaxially treated to control the Sc component at 10%, and a Sc component of 10% with a thickness of 20nm was obtained. 0.1 Al 0.9 N transition layer.

8. The preparation method according to claim 7, characterized in that Step S7 specifically includes: By molecular beam epitaxy equipment on Sc 0.2 Al 0.8 A GaN epitaxial layer with a thickness of 400 nm is grown on the N transition layer.

9. A large-area polycrystalline diamond GaN heterostructure having a graded Sc composition transition layer obtained by the preparation method according to any one of claims 1 to 8, characterized in that: It comprises a polycrystalline diamond substrate, a first ScAlN transition layer, a second ScAlN transition layer, a third ScAlN transition layer, a fourth ScAlN transition layer and a GaN epitaxial layer which are sequentially stacked from bottom to top; Wherein, a plurality of nano-columnar structures are formed in the upper region of the polycrystalline diamond substrate.

10. The large-area polycrystalline diamond GaN heterostructure with a graded Sc composition transition layer according to claim 9, characterized in that: The first ScAlN transition layer is Sc 0.35 Al 0.65 N transition layer; The second ScAlN transition layer is Sc 0.3 Al 0.7 N transition layer; The third ScAlN transition layer is Sc 0.2 Al 0.8 N transition layer; The fourth ScAlN transition layer is Sc 0.1 Al 0.9 N transition layer.

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