Beta-silicon nitride single crystal substrate and liquid-phase preparation method thereof

Abstract

According to the method, a high-pressure induction heating furnace is adopted, and under the nitrogen atmosphere of 2-5 MPa, a graphite crucible with the inner wall coated with silicon carbide (SiC) and a porous SiC carbon source are utilized to control the nitrogen content in a silicon melt and stabilize components; by introducing 0.05-0.30 wt% of an aluminum or yttrium cosolvent, the nitrogen dissolving efficiency and wettability are improved, in the method, a 10-30 DEG C temperature gradient of a carbon source region and a seed crystal region is established, convection of a nitrogen-containing silicon melt is induced, epitaxial growth of the beta-SiN single crystal is promoted, and the growth of the beta-SiN single crystal is further improved by controlling the immersion depth and the cooling rate of the seed crystal. And finally, the (0001)-oriented high-quality beta-SiN single crystal substrate with the thickness larger than or equal to 500 m and the dislocation density smaller than or equal to 1 * 10 cm is prepared. Compared with the traditional PVT and CVD methods, the method provided by the invention can effectively reduce the growth temperature and thermal stress, inhibit Si evaporation and significantly improve the crystal size and quality, and is suitable for the field of high-frequency and high-power semiconductor device manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon nitride single crystal preparation, and in particular, to a β-silicon nitride single crystal substrate and a liquid-phase preparation method thereof. Background Art

[0002] Silicon nitride (Si3N4) is considered an ideal substrate material for fields such as semiconductor power modules and high-temperature structural components due to its excellent comprehensive properties, such as high thermal conductivity (β-Si3N4≈ 90 W m -1 K -1 ), low dielectric constant (ε ≈ 7–8), low dielectric loss (< 10 -3 ), and excellent mechanical properties (room temperature flexural strength > 1 GPa, fracture toughness 6–8 MPa·m 1 / 2 ). With the development trend of power electronic devices towards miniaturization and high power density, the demand for high-quality large-size silicon nitride single crystal substrates is increasing day by day.

[0003] Existing silicon nitride single crystal preparation technologies still face many challenges. The physical vapor transport (PVT) method requires sublimation deposition at extremely high temperatures of 1900–2200°C, and at the same time, the thermal gradient is greater than 100 K·cm -1 , which is extremely likely to cause thermal cracks and high dislocation defects, and the crystal size is limited, making it difficult to break through the scale of 10 mm in diameter; although the chemical vapor deposition (CVD or RPCVD) method can achieve epitaxial growth of silicon nitride materials, the deposition rate is extremely low (usually <2 µm·h -1 ), only a thin film structure can be obtained, and the epitaxial stress during the deposition process is large, resulting in a dislocation density usually higher than 10 7 cm -2 . Although the high-pressure sintering (HPN) process can prepare silicon nitride green bodies, only polycrystalline forms can be obtained, and Y2O3-Al2O3 glass phase needs to be added, which will seriously reduce the dielectric and thermal properties of silicon nitride and is difficult to meet the requirements of high-end applications.

[0004] The liquid-phase epitaxy (LPE) method has attracted attention due to its low working temperature (≤1700°C), small thermal gradient, and potential high growth rate. However, due to the extremely low equilibrium solubility of nitrogen in the silicon melt (about 0.2-0.4 at%@1600°C, 1 MPa N2), and silicon is prone to a large amount of evaporation at high temperatures, and it is difficult to control the α / β phase and manage the transformation stress, the existing liquid-phase growth technologies can only obtain sub-millimeter-sized small grains, and the crystal quality fluctuates greatly, making it difficult to realize the industrial preparation of large-size single crystal substrates.

[0005] Therefore, there is an urgent need in the prior art to develop a new liquid phase epitaxy method that can effectively improve the nitrogen solubility, stabilize the melt composition, precisely control the temperature difference and phase composition, so as to overcome the problems of small crystal size, high defect density, low phase purity and thermal stress existing in the traditional methods, thereby realizing the preparation of large-size and high-quality β-Si3N4 single crystal substrates and meeting the urgent needs of high-performance silicon nitride substrate materials in fields such as power devices and high-temperature electronic devices. Summary of the Invention

[0006] One of the technical problems to be solved by the present invention is to provide a liquid phase preparation method for β-silicon nitride single crystal substrates, so as to solve the problems of low nitrogen dissolution efficiency, large melt composition fluctuation, difficulty in controlling the α / β phase purity, high crack and dislocation density caused by thermal stress in the prior art, and the technical problem of being unable to obtain β-Si3N4 single crystal substrates with large thickness, large size and high quality.

[0007] In order to overcome the above defects of the prior art, the present invention provides a liquid phase preparation method for β-silicon nitride single crystal substrates, comprising the following steps: S1: Set a carbon source and a silicon source in a graphite crucible to form a silicon melt capable of dissolving nitrogen; S2: Arrange a (0001)-oriented seed crystal above the silicon melt in step S1, and control a gap to be maintained between the surface of the seed crystal and the liquid surface of the silicon melt; S3: Evacuate and fill high-purity nitrogen into the graphite crucible, melt the silicon source and dissolve nitrogen, and establish a longitudinal temperature gradient to induce solution convection; S4: Control the seed crystal to immerse into the silicon melt, and slowly cool down to achieve epitaxial growth of β-Si3N4 single crystal; S5: After the seed crystal in step S4 finishes growing, cool, anneal and sample to obtain a β-silicon nitride single crystal substrate.

[0008] In a possible implementation manner, in step S1, the outer diameter of the graphite crucible is 200–1000 mm, and the inner wall of the graphite crucible is coated with a SiC layer with a thickness of 100–300 μm.

[0009] Compared with the prior art, the β-silicon nitride single crystal substrate of the present application has the following advantages: In the preparation method of the present invention, porous SiC is provided at the bottom of the graphite crucible as a carbon source to form a stable carbon activity in the melt. Combining polysilicon and a cosolvent to jointly construct a silicon melt environment with high nitrogen solubility, low silicon volatilization, and low interfacial tension; suppressing silicon evaporation and stabilizing the melt composition through a high-pressure nitrogen atmosphere, and at the same time cooperating with zone heating to establish a longitudinal temperature difference to induce solution convection to continuously supply nitrogen sources; during the epitaxial process, adopting a precisely controlled seed crystal immersion and slow cooling strategy to further reduce the risk of thermal stress and lattice mismatch, promoting the preferential growth of β-Si3N4 single phase, and finally obtaining a high-quality β-Si3N4 single crystal substrate with large size, large thickness, and low dislocation density. Compared with the existing liquid phase method, the present invention can effectively improve the nitrogen dissolution efficiency, stabilize the melt composition, control the α / β phase purity, reduce growth defects, significantly improve the single crystal thickness and diameter expansion ability, and at the same time significantly reduce the energy consumption and the risk of thermal stress cracking. It solves the main technical problems existing in the traditional liquid phase method and PVT process, has good prospects for large-scale industrial application, effectively solves the core problems proposed in the background technology, has excellent application and promotion value, and is particularly suitable for the large-scale industrialization needs in the fields of power semiconductors, high-frequency communication devices, and high-temperature structural materials.

[0010] In a possible implementation manner, in the step S1, the carbon source is porous SiC with an open porosity of 20-40%, a pore diameter of 10-30 μm, and a thickness of 5-10 mm, and the porous SiC is arranged at the bottom of the graphite crucible; the silicon source is polysilicon with a purity of not less than 6N, and the silicon source is arranged above the porous SiC; a cosolvent is further added to the polysilicon, and the cosolvent is aluminum or yttrium, and its mass is 0.05-0.30 wt% of the polysilicon.

[0011] Compared with the prior art, adopting the above technical solution can form a stable and controllable carbon activity in the melt through porous SiC, promote the equilibrium reaction between Si and C at high temperature, thereby significantly increasing the solubility of nitrogen element in the silicon melt; at the same time, adding aluminum or yttrium cosolvent can further reduce the surface tension of the melt, optimize the wettability of the seed crystal, and form AlN or YN nano coordination bodies to enhance the chemical nitrogen dissolution ability, which can effectively stabilize the melt composition, prevent the composition fluctuation caused by Si volatilization, improve the N concentration in the solution and the quality stability of the growth interface, and thus is conducive to the large-size and high-quality epitaxial growth of the subsequent β-Si3N4 single crystal. Through the collaborative optimization of the above multiple process parameters, the dynamic balance of the solution composition, carbon activity, and interface state is achieved, significantly improving the growth rate and crystal quality, and solving the problems of low nitrogen solubility, precipitation of heterogeneous phases, and composition out-of-control during the growth of silicon nitride single crystals by the existing liquid phase method.

[0012] In a possible implementation, in step S2, the seed crystal is a 4H-SiC seed crystal or a c-plane sapphire seed crystal. The diameter of the seed crystal is 100–300 mm, the thickness is 300–500 μm, and the surface roughness Ra is less than 0.5 nm.

[0013] Compared with the prior art, adopting the above technical solution, by selecting a 4H-SiC (0001) seed crystal or a sapphire c-plane seed crystal with excellent crystal orientation consistency as the epitaxial substrate, the heteroepitaxial nucleation control accuracy is significantly improved, promoting the preferential orientation growth of β-Si3N4 single crystal in the (0001) direction; further controlling the specific size of the seed crystal and the surface roughness Ra less than 0.5 nm helps to reduce the interfacial energy barrier during initial nucleation, reduce the number of dislocation sources, improve the integrity and flatness of the epitaxial layer, ensure the formation of a β-Si3N4 single crystal layer with high orientation, low dislocation density and excellent surface quality during the epitaxial growth process, guarantee the crystallization quality and size consistency of the obtained single crystal, and overcome the problems of heterogeneous impurities and crystal distortion existing in the traditional liquid-phase epitaxial growth.

[0014] In a possible implementation, in step S3, the conditions for evacuating and filling with high-purity nitrogen are as follows: evacuate to a pressure not higher than 1×10 -3 mbar in the graphite crucible, and then fill with nitrogen with a purity of 99.999% to a pressure of 2-5 MPa.

[0015] Compared with the prior art, adopting the above technical solution, by pre-evacuating, the residual gas impurities (including oxygen, water vapor, etc.) in the crucible are effectively removed, avoiding the contamination of the melt and crystal growth interface by oxidation impurities at high temperature. At the same time, by pressurizing with high-purity nitrogen to 2–5 MPa, the evaporation loss of silicon is effectively inhibited during the heat treatment and epitaxial growth process, the melt composition is stabilized, the dissolution concentration of nitrogen in the silicon melt is further increased, the composition is kept uniform, and the crystal defects caused by melt fluctuations are prevented.

[0016] In a possible implementation, in step S3, the conditions for melting the silicon source and dissolving nitrogen are as follows: heat the silicon source at a rate of 10-15 ℃·min -1 to 1500-1600℃ and hold for 1-3 h, so that the nitrogen content in the melt reaches 0.2-0.4 at %, to promote the dissolution of nitrogen in the silicon melt.

[0017] Compared with the prior art, adopting the above technical solution, by the controlled heating rate (10-15 ℃·min -1)( ) and a moderate heat preservation temperature (1500 - 1600 °C). While ensuring the full melting of the silicon source, it controls the dissolution process of nitrogen into the silicon melt, promotes the stable accumulation of nitrogen concentration in the melt, forms a solution environment with controllable nitrogen content and uniform composition, and avoids the risk of intense silicon evaporation caused by rapid heating or the precipitation of α-Si3N4 phase due to too high temperature. Through the coordinated optimization of temperature and time, it effectively balances the nitrogen dissolution rate and melt stability, thus ensuring a good solution composition basis at the initial stage of epitaxial growth.

[0018] In a possible implementation manner, in the step S3, the condition for establishing the longitudinal temperature gradient to induce solution convection is: through zone heating control, the temperature of the carbon source region is higher than that of the seed crystal region by 10 - 30 °C, and the pressure is maintained with a nitrogen flow rate of 50 - 150 sccm.

[0019] Compared with the prior art, adopting the above technical solution can induce stable thermal convection inside the melt by establishing a longitudinal temperature difference ΔT of 10 - 30 °C between the carbon source region and the seed crystal region, thereby continuously transporting the silicon melt rich in nitrogen to the surface of the seed crystal. At the same time, the system pressure is maintained by a microflow of nitrogen with a flow rate of 50 - 150 sccm, which helps to further stabilize the convection mode and interface environment, improve the solute transport efficiency, avoid solute depletion on the surface of the seed crystal, and maintain the continuity and flatness of the growth interface.

[0020] In a possible implementation manner, in the step S4, the condition for controlling the immersion of the seed crystal into the silicon melt is: controlling the immersion depth of the seed crystal into the silicon melt to be 1 - 3 mm; the condition for slowly cooling to achieve the epitaxial growth of β-Si3N4 single crystal is: growing β-Si3N4 single crystal on the surface of the seed crystal at a cooling rate of 1 - 5 °C / h, with a total temperature drop of 40 - 60 °C and a growth time of 24 - 72 hours.

[0021] Compared with the prior art, adopting the above technical solution can achieve local wetting rather than complete immersion of the melt-seed crystal interface by precisely controlling the slight immersion depth of the seed crystal by 1 - 3 mm, reduce the additional stress caused by the meniscus, and at the same time maintain the smooth expansion of the epitaxial growth interface. Combined with the slow cooling of 1 - 5 °C / h and the total temperature range control of 40 - 60 °C, the synergistic effect enables crystal growth to occur in an environment with moderate thermodynamic driving force and stable interface, promotes the directional epitaxial growth of β-Si3N4 single crystal, inhibits spontaneous nucleation and polycrystal formation, and reduces the generation of dislocations and microcracks.

[0022] In a possible implementation, in step S5, the conditions for cooling, annealing, and sampling are as follows: the cooling rate is 3–5 °C / min. After cooling to 1200 °C, the pressure is released to atmospheric pressure, and a 55 wt% KOH solution is used to perform thermal etching and chemical mechanical polishing on the product to remove residual silicon and surface defects.

[0023] Compared with the prior art, adopting the above technical solution can control a relatively mild cooling rate (3–5 °C / min), maintain a high-pressure nitrogen environment in the high-temperature to medium-temperature range (1200 °C), effectively avoid thermal stress concentration and microcrack generation caused by sharp temperature gradient changes, and at the same time ensure the stable crystal structure of β-Si3N4 formed by epitaxial growth and limited dislocation expansion. After cooling to 1200 °C, releasing the pressure helps prevent silicon volatilization and crystal surface peeling. Subsequently, selective etching of surface residual free silicon by thermal etching with a 55 wt% KOH solution, combined with chemical mechanical polishing (CMP), removes surface microdefects to achieve surface planarization treatment, further improving the quality and purity of the crystal surface, reducing surface roughness, and eliminating microscopic stress concentration areas.

[0024] Another technical problem to be solved by the present invention is to provide a β-silicon nitride single crystal substrate to solve the problems existing in the prior art, such as insufficient thickness, limited diameter, high α / β phase impurity content, poor orientation consistency, large dislocation density, and difficulty in meeting the requirements of high-end application fields for material quality and size scale.

[0025] To overcome the above defects of the prior art, the present invention provides a β-silicon nitride single crystal substrate prepared by the liquid-phase method for preparing the above β-silicon nitride single crystal substrate. The α-Si3N4 content of the β-silicon nitride single crystal substrate is ≤1 %, the phase purity is ≥99 %, its diameter is ≥100 mm, its thickness is ≥1 mm, its crystal orientation is (0001), the orientation deviation is ≤0.2°, and its dislocation density is ≤1 × 10 5 cm -2 .

[0026] Compared with the prior art, a β-silicon nitride single crystal substrate of the present application has the following advantages: Through comprehensive technical improvements in aspects such as stable solution composition, carbon activity buffering, nitrogen solubility enhancement, thermal convection optimization, and epitaxial interface regulation, the β-silicon nitride single crystal substrate of the present invention significantly improves the growth thickness and diameter expansion ability of β-Si3N4 single crystals, and successfully prepares large-size single crystals with a thickness ≥ 1 mm and a diameter ≥ 100 mm. At the same time, through precise temperature control and slow cooling processes, the present invention effectively inhibits the precipitation of the α-β-Si3N4 phase, achieving a high phase purity (≥ 99%) and a low α-phase impurity content (≤ 1%). And with optimized seed crystal selection and wetting control, the obtained single crystal has its crystal orientation maintained in the (0001) direction, with an orientation deviation ≤ 0.2°, ensuring the integrity of the crystal structure and orientation consistency. In addition, dislocation control technology reduces the final dislocation density to ≤ 1×10 5 cm -2 , which is significantly better than β-Si3N4 single crystals prepared by traditional liquid-phase and gas-phase methods. Through the synergistic effect of the above various process parameters and control means, the present invention effectively solves the problems existing in the prior art, such as small size, many impurities, poor quality, and large stress, significantly improves the overall performance of the β-silicon nitride single crystal substrate, and provides a solid material basis and technical support for its large-scale applications in fields such as power semiconductors, high-frequency communications, thermal management systems, and high-temperature structural materials. Description of the Drawings

[0027] Figure 1 is a schematic diagram of the growth process of a silicon nitride single crystal; Description of the Reference Numerals: 1. Graphite crucible; 2. SiC-C composite support; 3. Seed crystal; 4. Silicon source; 5. Carbon source. Detailed Embodiments

[0028] First of all, those skilled in the art should understand that these embodiments are only used to explain the technical principles of the embodiments of the present application and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments according to needs to adapt to specific application scenarios.

[0029] In the embodiments of the present application, unless otherwise clearly specified and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "below" and "beneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0030] The present invention provides a liquid-phase preparation method for a β-silicon nitride single-crystal substrate, comprising the following steps: S1: A carbon source and a silicon source are arranged in a graphite crucible to form a silicon melt capable of dissolving nitrogen; S2: A seed crystal with (0001) orientation is arranged above the silicon melt in the step S1, and a gap is maintained between the surface of the seed crystal and the liquid surface of the silicon melt; S3: The inside of the graphite crucible is evacuated and filled with high-purity nitrogen, the silicon source is melted and nitrogen is dissolved, and a longitudinal temperature gradient is established to induce solution convection; S4: The seed crystal is controlled to immerse in the silicon melt, and the temperature is slowly decreased to achieve epitaxial growth of β-Si3N4 single crystal; S5: After the seed crystal in the step S4 is grown, it is cooled, annealed and sampled to obtain a β-silicon nitride single-crystal substrate.

[0031] As a preferred solution, in the step S1, the outer diameter of the graphite crucible is 200–1000 mm, and the inner wall of the graphite crucible is coated with a SiC layer with a thickness of 100–300 μm.

[0032] The present invention proposes a liquid-phase preparation method for a high-quality β-silicon nitride single-crystal substrate, which inhibits Si evaporation, reduces thermal stress while ensuring nitrogen solubility, and realizes controllable growth of β-Si3N4 single phase, thereby preparing a large-size single-crystal substrate with a dislocation density ≤1 × 10 5 cm -2 and a thickness ≥500 µm; through the synergistic process of high-pressure nitrogen, porous SiC carbon activity buffering, and low-gradient temperature reduction, the nitrogen solubility of the melt is significantly improved, and a (0001)-oriented β-Si3N4 single-crystal substrate with a thickness ≥1 mm, a dislocation density ≤1 × 10 5 cm -2 and a diameter that can be extended to 6–8 inches is successfully prepared at a temperature ≤1700 °C, which not only completely solves the problems of insufficient nitrogen dissolution, α / β phase out-of-control and thermal cracks in the traditional liquid-phase method, but also significantly reduces the energy consumption compared with the PVT method, meeting the large-scale industrialization requirements of power semiconductor heat dissipation and high-frequency packaging.

[0033] As a preferred solution, in the step S1, the carbon source is porous SiC with an open porosity of 20-40%, a pore diameter of 10-30 μm, and a thickness of 5–10 mm, and the porous SiC is arranged at the bottom of the graphite crucible; the silicon source is polysilicon with a purity not less than 6N, and the silicon source is arranged above the porous SiC; a cosolvent is added to the polysilicon, and the cosolvent is aluminum or yttrium, and its mass is 0.05-0.30 wt% of the polysilicon.

[0034] As a preferred solution, in the step S2, the seed crystal is a 4H-SiC seed crystal or a c-plane sapphire seed crystal. The diameter of the seed crystal is 100–300 mm, the thickness is 300–500 μm, and the surface roughness Ra is less than 0.5 nm.

[0035] As a preferred solution, in the step S3, the conditions for evacuating and filling with high-purity nitrogen are as follows: evacuate until the air pressure in the graphite crucible is not higher than 1×10 -3 mbar, and then fill with nitrogen with a purity of 99.999% to a pressure of 2-5 MPa.

[0036] As a preferred solution, in the step S3, the conditions for melting the silicon source and dissolving nitrogen are as follows: heat the silicon source at a rate of 10-15 °C·min -1 to 1500-1600 °C and keep it warm for 1-3 h, so that the nitrogen content in the melt reaches 0.2-0.4 at %, to promote the dissolution of nitrogen in the silicon melt.

[0037] As a preferred solution, in the step S3, the conditions for establishing a longitudinal temperature gradient to induce solution convection are as follows: through zone heating control, make the temperature of the carbon source area 10–30 °C higher than that of the seed crystal area, and maintain the pressure with a nitrogen flow rate of 50-150 sccm.

[0038] As a preferred solution, in the step S4, the conditions for controlling the immersion of the seed crystal into the silicon melt are as follows: control the immersion of the seed crystal into the silicon melt by 1–3 mm; the conditions for slowly cooling to achieve the epitaxial growth of β-Si3N4 single crystal are as follows: make the β–Si3N4 single crystal epitaxially grow on the surface of the seed crystal at a cooling rate of 1–5 °C / h, the total cooling amount is 40–60 °C, and the growth time is 24–72 hours.

[0039] As a preferred solution, in the step S5, the conditions for cooling, annealing and sampling are as follows: the cooling rate is 3–5 °C / min. After cooling to 1200 °C, start to release pressure to atmospheric pressure, and use a 55wt% KOH solution to perform thermal etching and chemical mechanical polishing on the product to remove residual silicon and surface defects.

[0040] The above-preferred technical features of the present invention do not exist in isolation but form an organic cooperation and mutually promoting synergistic effect. Specifically, by setting a porous SiC carbon source and a high-purity polysilicon source in a graphite crucible and introducing aluminum or yttrium as a flux, the present invention can simultaneously regulate the carbon activity of the melt and enhance the solubility of nitrogen, stabilize the melt composition and inhibit silicon evaporation; through a high-pressure nitrogen atmosphere combined with vacuum pretreatment, impurities are effectively removed and the melt is kept pure, further improving the nitrogen dissolution efficiency; zone heating forms a moderate longitudinal temperature gradient and a microfluidic nitrogen flow rate, stably inducing solution convection, ensuring continuous delivery of the nitrogen-rich solution to the growth interface, and inhibiting solute depletion; precise control of the seed crystal gap and moderate immersion, combined with a slow and precise cooling strategy, effectively reduce thermal stress and dislocation generation, and promote the preferential epitaxial growth of single-phase β-Si3N4; finally, by controlling the cooling process and subsequent KOH thermal etching + CMP treatment, not only are surface residual stress and free silicon contamination eliminated, but the surface quality and flatness of the single crystal are further improved.

[0041] The various measures of the present invention are closely linked and the synergistic effect is significant. Through the full-process control from the source solution preparation, melt stabilization, epitaxial growth to cooling and sampling, a systematic breakthrough in low-temperature and high-efficiency nitrogen dissolution, single-phase stable growth, defect suppression and surface quality improvement is achieved. Finally, a high-quality large-size (0001)-oriented β-Si3N4 single crystal substrate with a thickness ≥ 1 mm, a diameter ≥ 100 mm, and a dislocation density ≤ 1 × 10 5 cm -2 and an α-Si3N4 content ≤ 1% is prepared, effectively solving the core problems such as insufficient nitrogen dissolution, composition fluctuation, thermal cracks and high dislocation density in the background technology. The overall technical effect is far superior to the existing liquid phase method and PVT method, and has extremely high industrial application value.

[0042] The present invention also provides a β-silicon nitride single crystal substrate prepared by the liquid phase method for preparing the above β-silicon nitride single crystal substrate. The α-Si3N4 content of the β-silicon nitride single crystal substrate is ≤ 1%, the phase purity is ≥ 99%, its diameter is ≥ 100 mm, its thickness is ≥ 1 mm, its crystal orientation is (0001), the orientation deviation is ≤ 0.2°, and its dislocation density is ≤ 1 × 10 5 cm -2 .

[0043] In the present invention, the equipment used, the reaction process and the reaction principle are as follows: 1. Equipment and loading As Figure 1 shown, Figure 1 is a schematic diagram of the silicon nitride single crystal growth process of the present invention, Figure 1Among them, it includes a graphite crucible 1. The carbon source 5 is porous silicon carbide, which is arranged at the inner bottom of the graphite crucible 1. The silicon source 4 (6N polysilicon) is placed on the upper part of the porous silicon carbide. The seed crystal 3 is fixed on the SiC-C composite support 2. One end of the SiC-C composite support 2 is connected to the top of the graphite crucible 1. The seed crystal 3 is fixed through the SiC-C composite support 2, and the SiC-C composite support 2 can be displaced in the vertical direction, thereby controlling the seed crystal 3 to enter the silicon source 4.

[0044] Specifically, it includes: Equipment: A high-pressure induction heating furnace is used, which can withstand 2–5 MPa of nitrogen; Graphite crucible: The inner wall of the graphite crucible is coated with 100–300 µm of SiC, and the outer diameter is 200–1000 mm; The carbon source (porous SiC (open porosity 20–40%)) and the silicon source (6N polysilicon) are placed at the bottom of the crucible; through the reaction Si(ℓ)+C⇌SiC, the silicon activity of the melt can be moderately reduced, thereby increasing the solubility of nitrogen in the melt, ensuring the thermodynamic equilibrium of the N concentration and C concentration throughout the growth process, and avoiding fluctuations in the C / Si ratio caused by Si evaporation. The porous structure can increase the specific surface area, and the melt can "penetrate" into the pores and dissolve carbon uniformly, thus avoiding the formation of heterogeneous SiC particles on the seed crystal / epitaxial surface.

[0045] Flux: 0.05-0.3 wt % of Al (or Y) is added to the raw materials to form AlN and YN nano coordination ligands in the Si melt, improving the chemical nitrogen dissolution ability. Al / Y reduces the surface tension γ of the melt and reduces the wetting angle θ of the seed crystal interface.

[0046] Seed crystal: (0001) orientation 4H-SiC or sapphire c-plane, with a diameter of 100-300 mm, a thickness of 300-500 µm, and Ra <0.5 nm; the surface of the seed crystal is 3–5 mm away from the initial liquid level of the melt, fixed through the SiC-C composite support and the immersion depth can be finely adjusted; The reaction process and principle are as follows: Evacuation and nitrogen filling: After sealing the furnace, evacuate to ≤1×10 -3 mbar; introduce 99.999% N2 to boost the pressure to 2–5 MPa (more preferably 3 MPa), stop inflating and stabilize the pressure. During the reaction process, the volatilization of Si(g) is inhibited by high pressure, keeping the melt composition constant, increasing the melt density and making the convection more stable, and increasing the N concentration in the solution; Melting and nitrogen dissolution: At a rate of 10–15°C·min -1Heat up to 1500 - 1600 °C; hold for 2 h to promote the dissolution of nitrogen in the melt and react with the porous SiC region to form a stable C activity; Establish a temperature gradient (ΔT): Through zone power control, make the temperature difference in the carbon source region higher than that in the seed crystal region in the longitudinal direction ΔT = 10 - 30 °C, turn on nitrogen at 50 - 150 sccm to maintain pressure, and induce Si - N melt - gas convection. The longitudinal ΔT generates convection and continuously transports the N - containing Si melt to the seed crystal interface;

[0047] Epitaxial growth: Immerse the seed crystal into the melt to a depth of 1 - 3 mm, maintain the balance of "wetting - non - immersion" of the liquid surface to reduce the meniscus stress. Immersing 1 - 3 mm can induce the growth of the epitaxial layer on the seed crystal surface without forming multi - point wetting. Then, cool the seed crystal region at a rate of 1 - 5 °C·h -1 Cool the seed crystal region, with a total temperature drop of 40 - 60 °C; grow for 24 - 72 h to obtain a 1 mm - 10 mm β - Si3N4 epitaxial layer; Cooling and post - treatment: After turning off the power, cool at a rate of 3 - 5 °C·min -1 Cool to 1200 °C and maintain the nitrogen pressure; naturally cool to 400 °C and then slowly release the pressure to atmospheric pressure, continue to room temperature and take out the sample, and complete the preparation through KOH thermal etching + CMP polishing.

[0048] To further explain the above - mentioned technical solutions of the present invention, specific examples combined with specific data and equipment are provided below to expand the content of the present invention: Example 1: This example provides a liquid - phase method for preparing a β - silicon nitride single - crystal substrate, and the preparation method includes the following steps: S1: Set the carbon source and silicon source to form a silicon melt that can dissolve nitrogen In a graphite crucible with an inner wall coated with a 200 - μm SiC layer and an outer diameter of 250 mm, place porous SiC with an outer diameter of 160 mm, a thickness of 6 mm, a porosity of 30%, and a pore diameter of 20 μm at the bottom as the carbon source; add 3.8 kg of polysilicon with a purity of 6N on the upper part of the porous SiC, and mix in 0.10 wt% of aluminum fluxing agent.

[0049] S2: Arrange the seed crystal Arrange a (0001) - oriented 4H - SiC seed crystal with a diameter of 100 mm, a thickness of 350 μm, and Ra of 0.4 nm above the silicon source, and control the gap between the seed crystal surface and the silicon melt liquid surface to be 4 mm.

[0050] S3: Evacuate, fill with nitrogen, melt and dissolve nitrogen, and establish a temperature gradient Evacuate the inside of the graphite crucible to 1×10 -3 mbar, and then fill it with nitrogen with a purity of 99.999% to a pressure of 3 MPa; heat it up to 1570°C at a rate of 10°C / min and hold for 2 hours to fully dissolve nitrogen in the silicon melt; through zone heating, make the temperature of the carbon source area 1586°C, the temperature of the seed crystal area 1568°C, the longitudinal temperature difference ΔT 18°C, and at the same time maintain the pressure with a nitrogen micro-flow of 80 sccm and induce solution convection.

[0051] S4: Control the immersion of the seed crystal and carry out epitaxial growth Slowly immerse the seed crystal into the silicon melt by 1.5 mm, control the cooling rate to be 1–3°C / h, the total cooling amount to be 60°C, and continuously carry out epitaxial growth for 48 hours.

[0052] S5: Cooling annealing and sampling Under the condition of maintaining the nitrogen pressure, cool it down to 1200°C at a rate of 3°C / min, then slowly release the pressure to atmospheric pressure, and continue to cool to room temperature. After taking out the sample, perform thermal etching treatment with a 55 wt% KOH solution (180°C), and carry out chemical mechanical polishing (CMP) to remove the residual silicon and defects on the surface, and finally obtain a β-silicon nitride single crystal substrate.

[0053] Final performance characterization results: The obtained β-Si3N4 single crystal substrate has a diameter of 100 mm, a thickness of 5.1 mm, a radial thickness difference of ±1 mm, an XRD full width at half maximum of 38 arcsec, and a dislocation density of 7.9×10 4 cm -2 , and the α-Si3N4 content is 0.5%.

[0054] In this example, liquid phase epitaxial growth was achieved on a seed crystal with a smaller size (Φ100 mm), and the carbon source ratio, flux concentration, and temperature gradient control conditions were systematically optimized. With a moderate carbon activity regulation and Al flux ratio, the nitrogen solubility was effectively improved and Si volatilization was inhibited. During the growth process, a detailed temperature difference design and a low-speed cooling strategy were adopted to effectively reduce the internal stress and defect formation. Finally, a high-quality β-Si3N4 single crystal substrate with a thickness of 5.1 mm, a dislocation density of 7.9×10 4 cm -2 , and an α-Si3N4 content of 0.5% was obtained, laying a foundation for further diameter expansion and application.

[0055] Example 2: This example provides a liquid phase method for preparing a β-silicon nitride single crystal substrate, and the preparation method includes the following steps: S1: Set the carbon source and silicon source to form a silicon melt that can dissolve nitrogen. In a graphite crucible with an inner wall coated with a 200-μm SiC layer and an outer diameter of 320 mm, place a porous SiC at the bottom with an outer diameter of 270 mm, a thickness of 6 mm, a porosity of 35%, and a pore diameter of 25 μm. Add 4.5 kg of polysilicon with a purity of 6N above the porous SiC, and mix in 0.15 wt% of aluminum and 0.05 wt% of yttrium as a flux.

[0056] S2: Arrange the seed crystal. Place a (0001)-oriented 4H-SiC seed crystal with a diameter of 150 mm, a thickness of 350 μm, and an Ra of 0.4 nm above the silicon source, and control the gap between the seed crystal surface and the silicon melt surface to be 4 mm.

[0057] S3: Evacuate, fill with nitrogen, melt and dissolve nitrogen, and establish a temperature gradient. Evacuate the inside of the graphite crucible to 1×10 -3 mbar, fill with nitrogen with a purity of 99.999% to a pressure of 4 MPa; heat at a rate of 10 °C / min to 1580 °C and hold for 3 hours; control the temperature of the carbon source area to be 1588 °C and the seed crystal area to be 1566 °C by zone heating, with a longitudinal temperature difference ΔT of 22 °C, and maintain the system stability with a nitrogen microflow of 80 sccm at the same time.

[0058] S4: Control the immersion of the seed crystal and carry out epitaxial growth. Slowly immerse the seed crystal 2 mm into the silicon melt, control the cooling rate to be 1–3 °C / h, with a total cooling amount of 50 °C, and continue epitaxial growth for 60 hours.

[0059] S5: Cooling annealing and sampling. Under the condition of maintaining the nitrogen pressure, cool at a rate of 3 °C / min to 1200 °C, then slowly release the pressure to atmospheric pressure and cool to room temperature. After taking out the sample, etch it with a 55 wt% KOH solution (180 °C) and polish it by CMP to remove the residual silicon and defects on the surface, and finally obtain a β-silicon nitride single crystal substrate.

[0060] Final performance characterization results: The obtained β-Si3N4 single crystal substrate has a diameter of 150 mm, a thickness of 8.2 mm, a radial thickness difference of ±1 mm, an XRD full width at half maximum of 35 arcsec, and a dislocation density of 6.3×10 4 cm -2 , and the α-Si3N4 content is 0.3%.

[0061] In this example, liquid-phase epitaxial growth was carried out on a large-size seed crystal (Φ150mm). A double flux system (Al+Y) was adopted and the nitrogen pressure was increased to 4MPa, significantly improving the nitrogen solubility and epitaxial growth uniformity. By controlling a large longitudinal temperature difference (ΔT = 22°C) and optimizing the cooling curve, the solution convection and continuous growth were effectively promoted. Finally, a high-quality β-Si3N4 single crystal with a thickness of 8.2mm and a dislocation density of 6.3×10 4 cm -2 and an α-Si3N4 content of 0.3% was obtained, demonstrating the superiority of this process in the preparation of large-size high-quality crystals.

[0062] Example 3: This example provides a liquid-phase method for preparing a β-silicon nitride single crystal substrate. The preparation method includes the following steps: S1: Set the carbon source and silicon source to form a silicon melt that can dissolve nitrogen In a graphite crucible with an inner wall coated with a 200μm SiC layer and an outer diameter of 320mm, a porous SiC with an outer diameter of 270mm, a thickness of 6mm, a porosity of 35%, and a pore diameter of 25μm is placed at the bottom; 4.5kg of polysilicon with a purity of 6N is added above the porous SiC, and 0.15wt% of aluminum flux is mixed in.

[0063] S2: Arrange the seed crystal A c-plane sapphire seed crystal with a diameter of 150mm, a thickness of 350μm, and a Ra of 0.4nm is arranged above the silicon source, and the gap between the seed crystal surface and the silicon melt surface is controlled to be 3mm.

[0064] S3: Vacuumize, fill with nitrogen, melt and dissolve nitrogen, and establish a temperature gradient The inside of the graphite crucible is evacuated to 1×10 -3 mbar, and nitrogen with a purity of 99.999% is filled to a pressure of 3.2MPa; it is heated to 1550°C at a heating rate of 10°C / min and held for 2 hours; the temperature of the carbon source area is 1580°C, the temperature of the seed crystal area is 1565°C, the longitudinal temperature difference ΔT is 15°C, and at the same time, the pressure is maintained stable with a nitrogen micro-flow of 100sccm.

[0065] S4: Control the immersion of the seed crystal and carry out epitaxial growth The seed crystal is immersed 2mm into the silicon melt, the cooling rate is controlled at 1–3°C / h, the total cooling amount is 45°C, and the epitaxial growth is continued for 72 hours.

[0066] S5: Cooling annealing and sampling Under the condition of maintaining nitrogen pressure, it was cooled to 1200 °C at a rate of 3 °C / min and then slowly depressurized to atmospheric pressure, and continued to be cooled to room temperature. After taking out the sample, it was thermally etched with 55 wt% KOH solution (180 °C), and assisted by CMP polishing to remove residual silicon and surface defects.

[0067] Final performance characterization results: The obtained β-Si3N4 single crystal substrate has a diameter of 150 mm, a thickness of 6.3 mm, a radial thickness difference of ±1 mm, an XRD full width at half maximum of 45 arcsec, and a dislocation density of 8.2×10 4 cm -2 , and the α-Si3N4 content is 0.8%.

[0068] In this example, the sapphire c-plane was used as the seed crystal. On the basis of optimizing the flux ratio (Al 0.15 wt%) and nitrogen pressure control (3.2 MPa), heteroepitaxial growth was achieved. By controlling a small temperature difference (ΔT = 15 °C), both the growth rate and interface stability were considered, and the expansion of macroscopic defects was avoided. Finally, a high-quality β-Si3N4 single crystal substrate with a thickness of 6.3 mm, a dislocation density of 8.2×10 4 cm -2 and an α-Si3N4 content of 0.8% was obtained, verifying the feasibility of the hetero-seed crystal process and providing technical support for applications under various substrate conditions.

[0069] Through the specific implementation results of the above examples, it further verified the effectiveness and advancement of the method for preparing β-silicon nitride single crystal substrate by the liquid phase method provided by the present invention: by introducing a high-pressure nitrogen environment, cooperating with a porous SiC carbon source to regulate the C / Si ratio and stable activity, and combining aluminum or yttrium flux to increase the nitrogen solubility and interface wettability, the dynamic stability of the silicon melt composition and the continuous supply of nitrogen concentration in the solution were synergistically achieved, effectively suppressing the problems of silicon volatilization and out-of-control phase transformation; at the same time, the present invention also adopted a reasonably designed longitudinal temperature gradient (ΔT) to induce stable convection and uniform growth, and by precisely controlling the immersion depth of the seed crystal and the cooling rate, the thermal stress and dislocation defect density during the epitaxial growth process were significantly reduced. Based on the above multiple process optimizations and synergistic effects, the present invention successfully prepared a high-quality (0001)-oriented β-silicon nitride single crystal substrate with a thickness ≥1 mm, a diameter ≥100 mm, a dislocation density ≤1×10 5 cm -2 and an α-Si3N4 content ≤1%, completely breaking through the technical bottlenecks of insufficient nitrogen dissolution, thermal cracks and difficult phase purity control in the traditional liquid phase method, and the energy consumption is much lower than that of the traditional PVT growth process, greatly promoting the industrial application of large-size and high-performance Si3N4 single crystal materials, and having important industrial promotion value and application prospects.

[0070] In the description of the embodiments of the present application, it should be noted that in the description of the present application, terms indicating directions or positional relationships such as "inner" and "outer" are based on the directions or positional relationships shown in the drawings. This is only for convenience of description and does not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present application.

[0071] In the description of the present application, the description referring to terms such as "one embodiment", "some embodiments", "in this embodiment", "specific example", or "some examples" means that the specific features, mechanisms, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0072] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a β-silicon nitride single crystal substrate by a liquid phase method, characterized in that, It includes the following steps: S1: Set a carbon source and a silicon source in a graphite crucible to form a silicon melt that can dissolve nitrogen; S2: Arrange a (0001)-oriented seed crystal above the silicon melt in step S1, and control to keep a gap between the surface of the seed crystal and the liquid surface of the silicon melt; S3: Evacuate the inside of the graphite crucible and fill it with high-purity nitrogen, melt the silicon source and dissolve nitrogen, and establish a longitudinal temperature gradient to induce solution convection; S4: Control the seed crystal to immerse into the silicon melt, and slowly cool down to achieve epitaxial growth of β-Si3N4 single crystal; S5: After the seed crystal in step S4 finishes growing, cool, anneal and sample to obtain a β-silicon nitride single crystal substrate.

2. The liquid-phase preparation method of the β-silicon nitride single crystal substrate according to claim 1, characterized in that, In step S1, the outer diameter of the graphite crucible is 200–1000 mm, and the inner wall of the graphite crucible is coated with a SiC layer with a thickness of 100–300 μm.

3. The liquid-phase preparation method of the β-silicon nitride single crystal substrate according to claim 1, characterized in that, In step S1, the carbon source is porous SiC with an open porosity of 20-40%, a pore diameter of 10-30 μm, and a thickness of 5–10 mm, and the porous SiC is arranged at the bottom of the graphite crucible; the silicon source is polysilicon with a purity not less than 6N, and the silicon source is arranged above the porous SiC; a flux is added to the polysilicon, and the flux is aluminum or yttrium, and its mass is 0.05-0.30 wt% of the polysilicon.

4. The liquid-phase preparation method of the β-silicon nitride single-crystal substrate according to claim 1, wherein, In step S2, the seed crystal is a 4H-SiC seed crystal or a c-plane sapphire seed crystal, the diameter of the seed crystal is 100–300 mm, the thickness is 300–500 μm, and the surface roughness Ra is less than 0.5 nm.

5. The liquid-phase preparation method of the β-silicon nitride single crystal substrate according to claim 1, characterized in that, In the step S3, the conditions for evacuating the air and filling with high-purity nitrogen are as follows: evacuate the air until the air pressure in the graphite crucible is not higher than 1×10 -3 mbar, and then fill with nitrogen with a purity of 99.999% until the pressure reaches 2-5 MPa.

6. The liquid-phase preparation method of the β-silicon nitride single crystal substrate according to claim 1, characterized in that, In the step S3, the conditions for melting the silicon source and dissolving nitrogen are as follows: the silicon source is heated at a rate of 10-15 °C·min -1 to 1500-1600 °C and held for 1-3 h, so that the nitrogen content in the melt reaches 0.2-0.4 at %, to promote the dissolution of nitrogen in the silicon melt.

7. The liquid-phase preparation method of the β-silicon nitride single crystal substrate according to claim 1, characterized in that, In step S3, the conditions for establishing the longitudinal temperature gradient to induce solution convection are: through zone heating control, the temperature of the carbon source area is 10–30 °C higher than that of the seed crystal area, and the pressure is maintained with a nitrogen flow rate of 50-150 sccm.

8. The liquid-phase preparation method of the β-silicon nitride single crystal substrate according to claim 1, characterized in that, In step S4, the conditions for controlling the seed crystal to immerse into the silicon melt are: control the seed crystal to immerse into the silicon melt by 1–3 mm; the conditions for slowly cooling down to achieve epitaxial growth of β-Si3N4 single crystal are: the seed crystal surface epitaxially grows β–Si3N4 single crystal at a cooling rate of 1–5 °C / h, the total temperature drop is 40–60 °C, and the growth time is 24–72 hours.

9. The liquid-phase preparation method of the β-silicon nitride single-crystal substrate according to claim 1, wherein, In step S5, the conditions for cooling, annealing and sampling are: the cooling rate is 3–5 °C / min, after cooling to 1200 °C, start to relieve pressure to atmospheric pressure, and use a 55 wt% KOH solution to perform thermal etching and chemical mechanical polishing on the product to remove residual silicon and surface defects.

10. A β-silicon nitride single crystal substrate prepared by the liquid phase method for preparing the β-silicon nitride single crystal substrate according to any one of claims 1-9, characterized in that, The α-Si3N4 content of the β-silicon nitride single crystal substrate is ≤1%, the phase purity is ≥99%, its diameter is ≥100 mm, its thickness is ≥1 mm, its crystal orientation is (0001), the orientation deviation is ≤0.2°, and its dislocation density is ≤1 × 10 5 cm -2 .

Images