A patterned epitaxial substrate with non-regular pentagon nano-islands, a preparation method thereof, a preparation method of an epitaxial wafer and application thereof

Abstract

This invention relates to the field of gallium oxide epitaxial technology, specifically to a patterned epitaxial substrate with non-regular pentagonal nanoislands, its fabrication method, epitaxial wafer fabrication method, and its applications. The fabrication method of the patterned epitaxial substrate with non-regular pentagonal nanoislands includes: forming a photoresist layer on a substrate; exposing and developing the photoresist layer using a photomask with a non-regular pentagonal shape; followed by hardening to form a photoresist mask with a non-regular pentagonal shape; and then performing solution modification and cleaning on the substrate with the photoresist mask to obtain the patterned epitaxial substrate with non-regular pentagonal nanoislands; wherein the non-regular pentagons have at least two sides of unequal length. Using this patterned epitaxial substrate with non-regular pentagonal nanoislands for epitaxial growth of gallium oxide thin films can break up substrate defects and early nucleation dislocations in the early nucleation layer, achieving a dislocation filtering effect; and this method is applicable to various substrates, not limited to homogeneous epitaxy.

Description

Technical Field

[0001] This invention relates to the field of gallium oxide epitaxial technology, and more specifically, to a patterned epitaxial substrate with non-regular pentagonal nanoislands, its preparation method, the preparation method of epitaxial wafers, and their applications. Background Technology

[0002] Existing technologies involve preparing periodic patterned structures (such as symmetrical frustums, hexagons, pyramidal protrusions, or trench arrays) on the surface of a substrate (such as sapphire), followed by gallium oxide epitaxial growth. The edges of the patterns are used to change the growth direction of the early nucleation layer and the dislocation propagation path, causing some penetrating dislocations to bend or terminate at the pattern boundaries.

[0003] However, the above-mentioned technologies have drawbacks: (1) Symmetrical patterns have limited filtering effect on specific dislocations: Although symmetrical patterns (frustums, regular hexagons, square stripes, etc.) can block some penetrating dislocations through lateral epitaxy (ELOG principle), gallium oxide is a monoclinic crystal system, and its slip system and main dislocation propagation direction are anisotropic. Symmetrical patterns are equivalent in all directions, and may not be able to optimally match the specific dislocation slip surface of gallium oxide, resulting in dislocations in some directions still being easy to pass through, and the filtering efficiency is not high enough.

[0004] (2) Stress concentration and defect introduction during initial nucleation and coalescence: When epitaxially growing on symmetrical discrete patterns (such as frustum arrays), the grains nucleated and grown at the top of different patterns are prone to new mosaic defects, small-angle grain boundaries or residual pores at the coalescence boundary due to the symmetrical shape of the growth front but complex crystal orientation matching. These defects become new dislocation sources and affect the uniformity of the film.

[0005] (3) Poor compatibility between the pattern shape and the gallium oxide nucleation interface: Common gallium oxide epitaxial surfaces (such as (001), (010) or (100)) do not perfectly match the curvature interface of symmetrical circular / hexagonal patterns. The isotropic nature of symmetrical patterns may lead to an increase in the diversity of crystal nucleus orientations in the early nucleation stage, which is not conducive to the formation of large-scale epitaxial layers with a single preferred orientation and may affect the uniformity of electrical / optical properties.

[0006] (4) Difficulty in achieving universality across different substrate systems: Existing symmetrical patterns are often optimized for specific substrates (such as sapphire) and specific epitaxial materials (such as GaN). When directly transplanted to gallium oxide epitaxy, or when different substrates (silicon, silicon carbide, quartz, etc.) are used, due to the differences in thermal expansion coefficient mismatch and lattice mismatch anisotropy, the symmetrical pattern often cannot flexibly adjust the nucleation strain, and the dislocation filtering effect will be greatly reduced.

[0007] Therefore, the existing method of preparing periodically symmetrical patterned structures on the substrate surface for gallium oxide epitaxial growth is difficult to effectively adapt to the anisotropic dislocation characteristics of the gallium oxide monoclinic crystal system due to the isotropic nature of the patterns. Furthermore, it is easy to introduce new defects during the nucleation and merging stage, which limits the dislocation filtering effect and the versatility on various types of substrates.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The primary objective of this invention is to provide a method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands. By setting a non-regular pentagonal pattern, the bending and breaking of the substrate at the initial nucleation layer will not penetrate the entire epitaxial layer, significantly reducing the dislocation density of the upper epitaxial layer. Specifically, using this patterned epitaxial substrate with non-regular pentagonal nanoislands for the epitaxial growth of gallium oxide thin films can break up substrate defects and early nucleation dislocations at the initial nucleation layer, achieving a dislocation filtering effect. Furthermore, this method is applicable to various substrates and is not limited to homogeneous epitaxy. It effectively solves the problems of epitaxial defects caused by the isotropic nature of symmetrical patterns in existing technologies and the difficulty in universal applicability to various substrate types.

[0010] A second objective of the present invention is to provide a patterned epitaxial substrate having non-regular pentagonal nanoislands.

[0011] A third objective of this invention is to provide a method for preparing an epitaxial wafer.

[0012] The fourth objective of this invention is to provide a method for preparing a patterned epitaxial substrate with non-regular pentagonal nanoislands, or a method for preparing a patterned epitaxial substrate or epitaxial wafer with non-regular pentagonal nanoislands, and its application in the preparation of power electronic devices, deep ultraviolet optoelectronic devices, and transparent conductive electrodes.

[0013] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention first provides a method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands, comprising the following steps: forming a photoresist layer on a substrate; exposing and developing the photoresist layer using a photomask with a non-regular pentagonal shape; and then hardening the photoresist layer to form a photoresist mask with a non-regular pentagonal shape; and performing solution modification and cleaning on the substrate with the photoresist mask to obtain a patterned epitaxial substrate with non-regular pentagonal nanoislands; wherein the non-regular pentagons have at least two sides of unequal length.

[0014] Furthermore, the substrate includes at least one of Ga2O3 substrate, SiC substrate, Si substrate, sapphire substrate and GaN substrate.

[0015] Furthermore, the substrate undergoes the following pretreatment: the substrate is sequentially cleaned with acetone, cleaned with ethanol, and rinsed with water, and then dried.

[0016] Furthermore, the photoresist layer is formed using positive photoresist, and the coating process for forming the photoresist layer includes: first spin coating at 400~600 rpm for 5~10 s, and then spin coating at 3000~4000 rpm for 30~45 s.

[0017] Furthermore, prior to the exposure, the photoresist layer is subjected to a soft baking treatment at a temperature of 70-100°C for a duration of 60-120 seconds.

[0018] Furthermore, the exposure employs a contact exposure method or a proximity exposure method, and the exposure dose is 50~80 mJ / cm². 2 The exposure time is 3-6 seconds. Alternatively, the exposure can be performed using a step-type exposure method, with an exposure time of 200-300 ms / shot.

[0019] Furthermore, the developing process employs an immersion developing method, with a developing time of 30-60 seconds and a developing temperature of 22-24°C. Alternatively, the developing process employs a spray developing method, with a developing time of 15-30 seconds and a developing temperature of 22-24°C.

[0020] Furthermore, the temperature of the hardening film is 110~120℃, and the hardening time is 80~100min.

[0021] Furthermore, the solution modification and cleaning specifically includes the following steps: first, heating and cleaning with acetone, then cleaning with ethanol, then soaking in hydrochloric acid, then rinsing with deionized water, then heating and soaking in a mixed acid solution of phosphoric acid and sulfuric acid, then rinsing with deionized water, then soaking in BOE solution, and finally rinsing with deionized water.

[0022] The present invention further provides a patterned epitaxial substrate with non-regular pentagonal nanoislands, which is prepared by the above-described method for preparing a patterned epitaxial substrate with non-regular pentagonal nanoislands.

[0023] The present invention provides a method for preparing an epitaxial wafer, including the above-mentioned method for preparing a patterned epitaxial substrate with non-regular pentagonal nanoislands, and further including the following steps: performing in-situ heat treatment and in-situ irradiation cleaning on the patterned epitaxial substrate with non-regular pentagonal nanoislands in sequence to expose the step flow morphology of the substrate, and then performing epitaxial growth on the patterned epitaxial substrate with non-regular pentagonal nanoislands to obtain an epitaxial wafer.

[0024] Furthermore, the in-situ heat treatment is performed at a temperature of 800~900℃ for 2~3 hours; during the in-situ heat treatment, multiple cycles of vacuuming and oxygen filling are carried out, with the oxygen filling pressure being 50~60MPa and the vacuuming pressure being -50~-60MPa.

[0025] Furthermore, the in-situ irradiation cleaning specifically includes the following steps: providing a metal source to the patterned epitaxial substrate and irradiating it in multiple pulses, wherein the pulse supply time is 10~12s and the pause time is 14~16s; after the pulse irradiation is completed, the temperature is raised to 1200~1280℃ and held for 10~12min to remove residual metal.

[0026] Further, the epitaxial growth specifically includes the following steps: epitaxial growth for 15-20 minutes, then stopping the epitaxial growth and performing high-temperature annealing, wherein the high-temperature annealing temperature is 1250-1280℃ and the time is 10-15 minutes, so as to block dislocations in the bottom layer; then performing continuous epitaxial growth until the epitaxial wafer is obtained.

[0027] The present invention also provides a method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands, or a method for fabricating a patterned epitaxial substrate or epitaxial wafer with non-regular pentagonal nanoislands, and its application in the fabrication of power electronic devices, deep ultraviolet optoelectronic devices and transparent conductive electrodes.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention uses photolithography to prepare and transfer patterns, which can obtain a patterned epitaxial substrate with a suitable asymmetric structure. Using it to grow gallium oxide thin films, defects such as substrate defects and early nucleation dislocations can be broken off in the early nucleation layer, thus achieving the effect of filtering dislocations.

[0029] (2) The present invention prepares a novel asymmetric non-regular pentagonal nano-island pattern on the substrate surface, which is applicable to various substrates and not limited to homoepitaxial growth, to grow gallium oxide thin films. It can break up defects such as substrate defects and early nucleation dislocations in the early nucleation layer, thereby achieving the function of filtering dislocations.

[0030] (3) The patterned epitaxial substrate with non-regular pentagonal nano-islands prepared by the present invention can be applied to a variety of epitaxial growth methods, such as metal-organic chemical vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE). Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 A partial structural schematic diagram of the patterned epitaxial substrate with non-regular pentagonal nanoislands provided by the present invention; Figure 2 Microscopic image of the epitaxial wafer prepared according to Example 1 of the present invention; Figure 3 Microscopic image of the epitaxial wafer prepared in Comparative Example 1 provided by the present invention; Figure 4 An atomic force microscope image of the epitaxial wafer prepared in Example 1 of this invention; Figure 5 An atomic force microscope image of the epitaxial wafer prepared in Comparative Example 1 provided by the present invention; Figure 6 A cross-sectional transmission electron microscope image of the epitaxial wafer prepared in Example 1 of this invention; Figure 7 A cross-sectional transmission electron microscope image of the epitaxial wafer prepared in Comparative Example 1 provided by the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0034] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0035] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0036] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0037] In a first aspect, the present invention provides a method for fabricating a patterned epitaxial substrate having non-regular pentagonal nanoislands for forming epitaxial wafers, comprising the following steps: A photoresist layer is formed on a substrate. The photoresist layer is exposed and developed using a photomask with a non-regular pentagon. Then, a hardening process is performed to form a photoresist mask with a non-regular pentagon, wherein the non-regular pentagon has at least two sides of unequal length, that is, at least one angle is not equal to 108°.

[0038] The substrate on which the photoresist mask is formed is subjected to solution modification and cleaning to obtain a patterned epitaxial substrate with non-regular pentagonal nanoislands. Here, in the patterned epitaxial substrate with non-regular pentagonal nanoislands, a nanoisland refers to a nanoscale, isolated, tiny protrusion structure fabricated on the substrate surface; non-regular pentagonal means that the top-view projection of the nanoisland is non-regular pentagonal.

[0039] A schematic diagram (top view) of a local structure of a patterned epitaxial substrate with non-regular pentagonal nanoislands. (See attached image) Figure 1 As shown, the top view projection of the non-regular pentagonal nano-island is a non-regular pentagon, and the non-regular pentagon has at least two sides of unequal length, that is, at least one angle is not equal to 108°.

[0040] In some specific embodiments, the substrate includes, but is not limited to, at least one of Ga2O3 (gallium oxide) substrate, SiC (silicon carbide) substrate, Si substrate, sapphire substrate and GaN (gallium nitride) substrate.

[0041] This invention utilizes a photolithography machine and a non-regular pentagonal photolithography plate for pattern transfer and fabrication, which can obtain a patterned epitaxial substrate with a suitable asymmetric structure. Using this substrate for epitaxial growth of gallium oxide thin films can break up defects such as substrate defects and early nucleation dislocations in the early nucleation layer, thereby achieving the effect of filtering dislocations.

[0042] This invention uses photolithography to prepare and transfer patterns, forming asymmetric, non-regular pentagonal nano-islands. By utilizing the edges of the patterns to change the growth direction of the early nucleation layer and the dislocation propagation path, some penetrating dislocations bend or terminate at the pattern boundaries, thereby blocking the upward extension of dislocations and achieving the effect of reducing the dislocation density of the epitaxial film.

[0043] Meanwhile, this invention prepares a novel asymmetric non-regular pentagonal nano-island pattern on the substrate surface, which is applicable to various substrates and not limited to homoepitaxial growth, to grow gallium oxide thin films. It can break up substrate defects and early nucleation dislocations in the early nucleation layer, thereby filtering dislocations.

[0044] Furthermore, the patterned epitaxial substrate with non-regular pentagonal nanoislands prepared by this invention can be applied to various epitaxial growth methods, such as metal-organic chemical vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE).

[0045] In addition, after the patterned substrate is prepared, solution modification and cleaning of the substrate pattern can make the edges of the pattern more regular and clean.

[0046] Therefore, this invention solves the problem that existing technologies using symmetrical figures with isotropic properties cannot optimally match β. Ga2O3 monoclinic crystal system has problems such as anisotropic dislocation slip planes, easy formation of new grain boundaries due to nucleation and merging, and poor versatility with multiple substrates.

[0047] In some specific embodiments, the side length of the non-regular pentagon is 4~6 nm, for example, 4 nm, 4.5 nm, 4.8 nm, 4.9 nm, 5.0 nm, 5.1 nm, 5.2 nm, 5.3 nm, 5.4 nm, 5.5 nm, or 6 nm; the angles of each corner of the non-regular pentagon are independently 100~120°, for example, 100°, 103°, 105°, 108°, 110°, 112°, 115°, 118°, or 120°, wherein at least one corner is not equal to 108°. The tilt of the angles is to match the characteristics of the gallium oxide monoclinic crystal system, so that gallium oxide will not have more dislocation slip and twin boundaries during epitaxial growth.

[0048] In some specific embodiments, the substrate undergoes the following pretreatment: the substrate is sequentially cleaned with acetone, cleaned with ethanol, and rinsed with water, and then dried; specifically, the substrate is sequentially cleaned with acetone for 5-10 minutes, cleaned with anhydrous ethanol for 5-10 minutes (repeated twice), and rinsed with deionized water for 10-20 minutes, and then dried with nitrogen. Epitaxial growth requires a high-quality substrate; otherwise, defects on the substrate surface will be inherited into the epitaxial layer during the epitaxial process. Therefore, substrate pretreatment is necessary to lay the foundation for subsequent epitaxial growth.

[0049] In some specific embodiments, the photoresist layer is formed using a positive photoresist such as AZ5214, and the coating process for forming the photoresist layer includes: first, spin coating at 400~600 rpm (e.g., 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm) for 5~10 seconds (e.g., 5 s, 6 s, 7 s, 8 s, 9 s, 10 s), and then at 3000~4000 rpm (e.g., 3000 rpm, 3200 rpm, 3300 rpm)... Spin coating at 3500rpm, 3600rpm, 3800rpm, and 4000rpm for 30~45s (e.g., 30s, 33s, 35s, 38s, 40s, 42s, and 45s), with an acceleration rate of 2000~5000rpm / s (e.g., 2000rpm / s, 2500rpm / s, 3000rpm / s, 3500rpm / s, 4000rpm / s, 4500rpm / s, and 5000rpm / s).

[0050] In some specific embodiments, prior to exposure, the photoresist layer undergoes a soft baking treatment to remove solvent. The soft baking temperature is 70–100°C, for example, 70°C, 75°C, 80°C, 90°C, or 100°C, and the soft baking time is 60–120 seconds, for example, 60 seconds, 70 seconds, 80 seconds, 90 seconds, 100 seconds, 110 seconds, or 120 seconds. Preferably, the soft baking temperature of the sapphire substrate is ≤80°C to prevent over-baking.

[0051] In some specific embodiments, the exposure is performed using a contact exposure method or a proximity exposure method, and the exposure dose for the contact exposure method or the proximity exposure method is 50~80 mJ / cm². 2 For example, 50mJ / cm 2 60mJ / cm 2 70mJ / cm 2 80mJ / cm 2 The exposure time for contact or proximity exposure methods is 3-6 seconds (corresponding to a mercury lamp with a power of 10-15 mW / cm). 2 (e.g., 3s, 4s, 5s, 6s).

[0052] In some specific implementations, the exposure adopts a step exposure method, and the exposure time of the step exposure method is 200~300ms / shot, such as 200ms / shot, 220ms / shot, 230ms / shot, 250ms / shot, 280ms / shot, 300ms / shot.

[0053] In some specific embodiments, the development is carried out by immersion development, and the development time of immersion development is 30~60s, for example 30s, 40s, 50s, 60s; the development temperature of immersion development is 22~24℃, for example 22℃, 23℃, 24℃.

[0054] In some specific embodiments, the developing method is spray developing, and the developing time of the spray developing method is 15~30s, for example 15s, 20s, 25s, 30s; the developing temperature of the spray developing method is 22~24℃, for example 22℃, 23℃, 24℃.

[0055] In some specific embodiments, the developing process may use AZ300MIF developer or MF-319 developer, but is not limited to these.

[0056] In some specific embodiments, the developing process involves rinsing with deionized water and then spin-drying.

[0057] In some specific embodiments, the hardening temperature is 110~120℃, for example 110℃, 112℃, 115℃, 118℃, 120℃; the hardening time is 80~100min, for example 80min, 85min, 90min, 95min, 100min; preferably, the hardening is performed on a hot plate. Hardening can enhance etching tolerance.

[0058] In some specific embodiments, the solution modification and cleaning specifically include the following steps: first, heating and cleaning with acetone, such as a water bath at 70-80°C for 5-10 minutes (replacing the solution twice during the process), then cleaning with ethanol, such as anhydrous ethanol, for 8-10 minutes, followed by soaking in hydrochloric acid for 5-8 minutes, then rinsing with deionized water for 5-10 minutes, then heating and soaking in a mixed acid solution of phosphoric acid and sulfuric acid (preferably at 80-90°C for 1-2 minutes, where the mass fraction of phosphoric acid is 75%-85% and the mass fraction of sulfuric acid is 90%-98%), then rinsing with deionized water for 5-8 minutes, then soaking in BOE solution for 3-5 minutes, and finally rinsing with deionized water for 5-8 minutes. The above solution modification can make the shape of the non-regular pentagonal patterned substrate more regular, and reduce the particles or impurities at the edges of the pattern, which is more conducive to epitaxially producing a defect-free epitaxial layer; further cleaning can make the epitaxial surface cleaner, remove surface contaminants, expose atomic steps on the surface, and make the epitaxial morphology flatter.

[0059] Secondly, the present invention provides a patterned epitaxial substrate having non-regular pentagonal nanoislands, which is prepared by the method described above for preparing a patterned epitaxial substrate having non-regular pentagonal nanoislands.

[0060] Using this patterned epitaxial substrate with non-regular pentagonal nanoislands to grow gallium oxide thin films can break up defects such as substrate defects and early nucleation dislocations in the early nucleation layer, thus achieving the effect of filtering dislocations.

[0061] Thirdly, the present invention provides a method for preparing an epitaxial wafer, including the above-mentioned method for preparing a patterned epitaxial substrate having non-regular pentagonal nanoislands, and further including the following steps: The patterned epitaxial substrate with non-regular pentagonal nanoislands is subjected to in-situ heat treatment and in-situ irradiation cleaning to expose the step flow morphology of the substrate. Then, epitaxial growth is performed on the patterned epitaxial substrate with non-regular pentagonal nanoislands to obtain an epitaxial wafer.

[0062] In particular, by sequentially performing in-situ heat treatment and in-situ metal irradiation on a patterned epitaxial substrate with non-regular pentagonal nano-islands, a series of cleaning processes can thoroughly obtain a fresh epitaxial surface, which is beneficial for subsequent epitaxial growth.

[0063] The epitaxial wafer preparation method provided by this invention can break up defects such as substrate defects and early nucleation dislocations in the early nucleation layer, thereby filtering out dislocations and achieving good film uniformity. In addition, this method is applicable to various substrates and is not limited to homoepitaxial growth.

[0064] In some specific embodiments, the temperature of the in-situ heat treatment is 800~900℃, for example 800℃, 830℃, 850℃, 880℃, or 900℃; and the time of the in-situ heat treatment is 2~3h, for example 2h, 2.5h, or 3h.

[0065] In some specific embodiments, the in-situ heat treatment process involves multiple cycles of vacuuming and oxygen filling. The oxygen filling pressure is 50~60MPa, for example, 50MPa, 52MPa, 53MPa, 55MPa, 58MPa, or 60MPa; the vacuuming pressure is -50~-60MPa, for example, -50MPa, -53MPa, -55MPa, -58MPa, or -60MPa.

[0066] In-situ heat treatment is performed in the epitaxial equipment, that is, the patterned epitaxial substrate with non-regular pentagonal nano-islands is baked at high temperature in the epitaxial chamber. During this period, multiple oxygen vacuuming and filling processes are performed, which can clean the growth chamber and ensure that all pipes of the equipment are in an oxygen atmosphere.

[0067] In some specific embodiments, the in-situ irradiation cleaning includes the following steps: providing a metal source, such as Ga or In (preferably a mixture of both in a molar ratio of 1:2), to the patterned epitaxial substrate, and irradiating it with multiple pulses, wherein the pulse supply time is 10-12 s (e.g., 10 s, 11 s, 12 s), and the pause time is 14-16 s (e.g., 14 s, 15 s, 16 s); after the pulse irradiation, the temperature is raised to 1200-1280℃ (e.g., 1200℃, 1220℃, 1230℃, 1250℃, 1260℃, 1280℃), and held for 10-12 min (e.g., 10 min, 11 min, 12 min) to remove residual metal. In-situ irradiation cleaning can thoroughly clean the substrate material, exposing a clear step flow morphology, which is beneficial for the subsequent growth of the epitaxial layer.

[0068] In some specific embodiments, the epitaxial growth specifically includes the following steps: epitaxial growth for 15-20 minutes (e.g., 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes), then stopping the epitaxial growth and performing high-temperature annealing. The high-temperature annealing temperature is 1250-1280℃ (e.g., 1200℃, 1220℃, 1230℃, 1250℃, 1260℃, 1280℃), and the high-temperature annealing time is 10-15 minutes (e.g., 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes). This can completely prevent dislocations from spreading to the epitaxial layer surface by blocking them at the bottom layer. Then, continuous epitaxial growth is performed until the epitaxial wafer is obtained. In the epitaxial growth process of this invention, a pause process for interrupting the layer is performed in the early stage of growth. This process can completely block defects and dislocations caused by the substrate in the early stage of epitaxial growth, achieving a high-quality epitaxial layer.

[0069] Therefore, the epitaxial wafer fabrication method provided by this invention includes the above-mentioned method for fabricating patterned epitaxial substrates with non-regular pentagonal nanoislands. First, various substrates are patterned to initially block most substrate defects from extending to the epitaxial layer. Then, the pattern on the patterned substrate is modified to make it more suitable for epitaxial growth. Next, substrate surface treatment processes such as in-situ cleaning and in-situ irradiation cleaning are performed. Finally, epitaxial growth is carried out, with an initial interruption of epitaxy to completely break off all substrate defects in the initial layer of the epitaxial layer. These four progressive steps form a superior epitaxial growth strategy. Together, they ensure the controllable fabrication of high-quality, high-flatness, low-defect gallium oxide single-crystal thin films, demonstrating significant advancement and practical value in the field of ultra-wide bandgap semiconductor epitaxial technology.

[0070] Fourthly, the present invention provides a method for preparing a patterned epitaxial substrate with non-regular pentagonal nanoislands, or a method for preparing a patterned epitaxial substrate with non-regular pentagonal nanoislands, or an epitaxial wafer, and its application in the preparation of power electronic devices, deep ultraviolet optoelectronic devices, and transparent conductive electrodes.

[0071] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0072] Example 1 The method for fabricating a patterned epitaxial substrate and epitaxial wafer with non-regular pentagonal nanoislands provided in this embodiment includes the following steps: (1) Clean the SiC substrate: First, clean it with acetone for 5 min, then clean it with anhydrous ethanol for 5 min and repeat twice, then rinse it with deionized water for 10 min, and finally dry it with nitrogen.

[0073] (2) Using a photolithography machine and a photolithography plate with a fixed non-regular pentagonal shape, patterns are transferred and fabricated to obtain a patterned epitaxial substrate with non-regular pentagonal nano-islands: Coating: Positive photoresist AZ5214 was used. The coating process was to first spin coat at a low speed of 500 rpm for 8 seconds, and then spin coat at a high speed of 3500 rpm for 38 seconds (acceleration rate was 3000 rpm / s). Softening to remove solvent: A hot plate is used to perform a softening treatment at 100°C for 60 seconds; Exposure: Contact exposure method is used, with an exposure dose of 60 mJ / cm². 2 Corresponding to a mercury lamp of 10mW / cm 2 Exposure time: 5 seconds; Development: AZ300MIF developer was used, and the immersion development method was used. The solution was immersed at 23°C for 40 seconds. After development, the solution was rinsed with deionized water and then spun dry. Hardening film to enhance etching resistance: A photoresist mask with non-regular pentagonal nano-islands was obtained by using a hot plate at 115°C for 80 min.

[0074] (3) Solution modification and cleaning of the substrate with the photoresist mask: The substrate is cleaned by heating in an acetone (75°C) in a water bath for 5 minutes (replacing the solution twice during the process), then cleaned with anhydrous ethanol for 8 minutes, then soaked in hydrochloric acid for 8 minutes, then rinsed with deionized water for 8 minutes, then soaked in a mixed acid solution of phosphoric acid and sulfuric acid (75%~85% by mass of phosphoric acid and 90%~98% by mass of sulfuric acid) at 85°C for 1 minute, then rinsed with deionized water for 6 minutes, then soaked in BOE solution for 5 minutes, and finally rinsed with deionized water for 5 minutes to obtain a patterned epitaxial substrate with non-regular pentagonal nanoislands, wherein the non-regular pentagons have at least two sides of unequal length.

[0075] (4) The patterned epitaxial substrate with non-regular pentagonal nanoislands prepared above is subjected to in-situ heat treatment in the epitaxial equipment, that is, high-temperature baking is performed in the epitaxial chamber, and in-situ heat treatment is carried out at 900°C for 2 hours. During this period, multiple cycles of vacuuming and oxygen filling are performed, wherein the oxygen filling pressure is 50 MPa and the vacuuming pressure is -50 MPa. This method can clean the growth chamber and keep all pipes of the equipment in an oxygen atmosphere.

[0076] (5) In-situ irradiation cleaning in epitaxial equipment: Ga and In metal sources (molar ratio of 1:2) are provided to the substrate for irradiation. Multiple pulses are performed (pulse supply for 10s, stop for 15s). After the pulse irradiation is completed, the temperature is raised to 1280℃ and held for 10min to remove metal residues. This can thoroughly clean the substrate material and expose a clear step flow morphology, which is beneficial to the subsequent growth of epitaxial layers.

[0077] (6) Epitaxial growth of gallium oxide thin film: Epitaxial growth begins, and after 15 minutes of growth, epitaxial growth is stopped, followed by high-temperature annealing at 1250℃ for 10 minutes. This completely reduces dislocations at the bottom layer, preventing them from propagating to the surface of the epitaxial layer. Continuous epitaxial processes are then performed to form a gallium oxide thin film, resulting in a qualified epitaxial wafer.

[0078] Example 2 The method for preparing the patterned epitaxial substrate and epitaxial wafer with non-regular pentagonal nanoislands provided in this embodiment differs from that in Example 1 in that the SiC substrate is replaced with a sapphire substrate.

[0079] Example 3 The method for preparing the patterned epitaxial substrate and epitaxial wafer with non-regular pentagonal nanoislands provided in this embodiment differs from that in Example 1 in that the SiC substrate is replaced with a GaN substrate.

[0080] Example 4 The method for preparing the patterned epitaxial substrate and epitaxial wafer with non-regular pentagonal nanoislands provided in this embodiment differs from that in Embodiment 1 in that: the in-situ heat treatment is carried out at 800°C for 3 hours, and the oxygen pressure during the multiple cycles of vacuuming and oxygen filling is 60 MPa, and the vacuuming pressure is -60 MPa.

[0081] Example 5 The difference between the patterned epitaxial substrate and epitaxial wafer with non-regular pentagonal nanoislands provided in this embodiment and that in Example 1 is that the temperature is raised to 1200°C and held for 12 minutes after the pulse irradiation ends.

[0082] Example 6 The method for preparing the patterned epitaxial substrate and epitaxial wafer with non-regular pentagonal nanoislands provided in this embodiment differs from that in Example 1 in that: after stopping epitaxial growth, it is annealed at 1280°C for 15 minutes.

[0083] Example 7 The method for preparing the patterned epitaxial substrate and epitaxial wafer with non-regular pentagonal nanoislands provided in this embodiment differs from that in Example 1 in that: Comparative Example 1 The comparative examples provided are conventional flat substrates and epitaxial wafers. The epitaxial wafers are prepared by MOCVD. The conventional flat substrates are prepared by conventional cutting, grinding, polishing and cleaning methods, without involving pattern transfer preparation or pattern modification operations similar to those of patterned substrates. The roughness of the flat substrates is 0.3 nm.

[0084] like Figures 2-7 The diagram illustrates the surface morphology, interface defects, and dislocation bending and filtering in two gallium oxide homoepitaxial structures, Example 1 and Comparative Example 1. Figure 2 This is a microscope image of the epitaxial wafer (with a gallium oxide thin film on the surface) prepared in Example 1. Figure 3 The image shows a microscopic image of the epitaxial wafer (gallium oxide thin film on the surface) prepared in Comparative Example 1. It can be seen that there are almost no defects on the epitaxial surface of the special substrate in Example 1, while there are many black wedge-shaped defects on the surface of the conventional flat substrate in Comparative Example 1. Figure 4 This is an atomic force microscope image of the epitaxial wafer (with a gallium oxide thin film on the surface) prepared in Example 1. Figure 5 The image shows an atomic force microscope image of the epitaxial wafer (gallium oxide thin film on the surface) prepared in Comparative Example 1. It can be seen that the surface roughness of the epitaxial wafer in Comparative Example 1 is significantly higher than that in Example 1. Figure 6 This is a cross-sectional transmission electron microscope image of the epitaxial wafer prepared in Example 1. Figure 7 The image shows a cross-sectional transmission electron microscope (TEM) image of the epitaxial wafer prepared in Comparative Example 1. It can be seen that in the cross-sectional image of the epitaxial wafer prepared in Example 1 using a non-regular pentagonal substrate, there are fewer defects extending upward above the epitaxial interface, while the epitaxial wafer prepared in Comparative Example 1 using a conventional substrate shows more defects and dislocations extending upward.

[0085] Comparative Example 2 The method for preparing the epitaxial wafer provided in this comparative example differs from that in Example 1 in that steps (4) and (5) are not performed.

[0086] Comparative Example 3 The difference between the preparation method of the epitaxial wafer provided in this comparative example and that in Example 1 is that high-temperature annealing was not performed in step (6).

[0087] Experimental Example The full width at half maximum (FWHM) of the gallium oxide thin films on the epitaxial wafers prepared in each embodiment and comparative example was measured, and the results are shown in Table 1. A smaller FWHM value indirectly indicates a lower dislocation density.

[0088] Table 1. Results of the full width at half maximum (FWHM) curves of the thin film layers on each epitaxial wafer.

[0089] As can be seen from Table 1, compared with Comparative Examples 1 to 3, the rocking curves obtained in each embodiment have lower half-width values, which indicates that the epitaxial layer dislocation density of each embodiment is lower.

[0090] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands, characterized in that, Includes the following steps: A photoresist layer is formed on a substrate, and the photoresist layer is exposed and developed using a photomask with a non-regular pentagon shape, and then hardened to form a photoresist mask with a non-regular pentagon shape. The substrate on which the photoresist mask is formed is subjected to solution modification and cleaning to obtain a patterned epitaxial substrate with non-regular pentagonal nano-islands; The non-regular pentagon has at least two sides of unequal length.

2. The method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands according to claim 1, characterized in that, The substrate includes at least one of Ga2O3 substrate, SiC substrate, Si substrate, sapphire substrate and GaN substrate; And / or, the substrate is pretreated as follows: the substrate is sequentially cleaned with acetone, cleaned with ethanol and rinsed with water, and then dried.

3. The method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands according to claim 1, characterized in that, The photoresist layer is formed using positive photoresist, and the coating process for forming the photoresist layer includes: first spin coating at 400~600 rpm for 5~10 s, and then spin coating at 3000~4000 rpm for 30~45 s. And / or, prior to the exposure, the photoresist layer is subjected to a soft baking treatment at a temperature of 70~100℃ for a duration of 60~120s.

4. The method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands according to claim 1, characterized in that, The exposure is performed using a contact exposure method or a proximity exposure method, and the exposure dose is 50~80 mJ / cm. 2 Exposure time is 3-6 seconds; Alternatively, the exposure may employ a step-by-step exposure method, with an exposure time of 200~300ms / shot.

5. The method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands according to claim 1, characterized in that, The development is carried out by immersion development, and the development time is 30~60s and the development temperature is 22~24℃; Alternatively, the developing process may employ a spray developing method, with a developing time of 15-30 seconds and a developing temperature of 22-24°C.

6. The method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands according to claim 1, characterized in that, The temperature of the hardening film is 110~120℃, and the hardening time is 80~100min; And / or, the solution modification and cleaning specifically includes the following steps: first, heating and cleaning with acetone, then cleaning with ethanol, then soaking in hydrochloric acid, then rinsing with deionized water, then heating and soaking in a mixed acid solution of phosphoric acid and sulfuric acid, then rinsing with deionized water, then soaking in BOE solution, and finally rinsing with deionized water.

7. A patterned epitaxial substrate with non-regular pentagonal nanoislands, characterized in that, It is prepared by the method for preparing a patterned epitaxial substrate with non-regular pentagonal nanoislands as described in any one of claims 1 to 6.

8. A method for preparing an epitaxial wafer, characterized in that, The method includes the fabrication method of a patterned epitaxial substrate having non-regular pentagonal nanoislands as described in any one of claims 1 to 6, and further includes the following steps: The patterned epitaxial substrate with non-regular pentagonal nanoislands is subjected to in-situ heat treatment and in-situ irradiation cleaning to expose the step flow morphology of the substrate. Then, epitaxial growth is performed on the patterned epitaxial substrate with non-regular pentagonal nanoislands to obtain an epitaxial wafer.

9. The method for preparing an epitaxial wafer according to claim 8, characterized in that, At least one of the following conditions must be met: (1) The temperature of the in-situ heat treatment is 800~900℃ and the time is 2~3h; the in-situ heat treatment process involves multiple cycles of vacuuming and oxygen filling, the pressure of oxygen filling is 50~60MPa, and the pressure of vacuuming is -50~-60MPa. (2) The in-situ irradiation cleaning specifically includes the following steps: providing a metal source to the patterned epitaxial substrate and irradiating it in multiple pulses, wherein the pulse supply time is 10~12s and the pause time is 14~16s; after the pulse irradiation is completed, the temperature is raised to 1200~1280℃ and held for 10~12min to remove residual metal. (3) The epitaxial growth specifically includes the following steps: epitaxial growth for 15~20 min, then stop epitaxial growth and perform high-temperature annealing, the temperature of the high-temperature annealing is 1250~1280℃ and the time is 10~15 min, so as to block dislocations in the bottom layer; then perform uninterrupted epitaxial growth until the epitaxial wafer is obtained.

10. The method for fabricating a patterned epitaxial substrate with non-regular pentagonal nanoislands as described in any one of claims 1 to 6, or the method for fabricating an epitaxial wafer with non-regular pentagonal nanoislands as described in claim 7, or the method for fabricating an epitaxial wafer as described in any one of claims 8 to 9, in the fabrication of power electronic devices, deep ultraviolet optoelectronic devices, and transparent conductive electrodes.

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