Method for removing bubbles in gallium oxide melt

Abstract

The invention belongs to the technical field of semiconductor material preparation, and particularly relates to a method for removing bubbles in gallium oxide melt. The method comprises a raw material pretreatment step, a segmented sintering step, regulation and control of process links such as crucible dynamic rotation control and the like, and through accurate control of key parameters such as forming pressure, sintering conditions and temperature, melt dynamic stirring, heat preservation time and the like, the removal rate of bubbles in gallium oxide melt and crystals can be increased to 92% or above; the dislocation density is controlled below 2.5 * 10 < 3 > cm <-2 >, and the resistivity radial deviation is less than or equal to 3%. The process method disclosed by the invention is efficient and economical, reduces process links and potential pollution sources, ensures the purity and reliability of the product, and also reduces the operation difficulty and time cost. According to the technical scheme, the technical problems of crystal defect increase and performance reduction caused by bubbles are directly solved, the overall quality of the crystal is improved, and the obtained gallium oxide crystal better meets the high-standard requirements of high-performance electronic devices for materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor material preparation, and particularly relates to a bubble removal technology in a gallium oxide single crystal growth process, which improves the quality and purity of a crystal product. BACKGROUND

[0002] As an important ultra-wide bandgap semiconductor material, the fourth generation semiconductor gallium oxide has a bandgap of 4.9 eV, and the theoretical breakdown field strength of a beta-gallium oxide single crystal material can reach 8 MV / cm, which is much higher than the limit of materials such as GaN and SiC. In addition, under the same withstand voltage, gallium oxide-based power devices have lower on-resistance, higher power conversion efficiency and lower on-state loss, and have broad application prospects in electronic and power systems in the fields of new energy vehicles and rail transit.

[0003] In the gallium oxide single crystal growth process, the existence of bubbles in the melt can affect the quality of the crystal, leading to an increase in crystal defects and a decrease in performance. These bubbles are mainly caused by impurities and residual gas in the powder raw material, in addition to factors such as temperature fluctuations or pressure changes during the growth process. Although the industry has taken a series of measures to reduce the generation of bubbles, such as optimizing the purity of the raw material and precisely controlling the growth conditions, existing technical methods still cannot completely eliminate these bubbles. Therefore, how to effectively remove the bubbles in the gallium oxide solution and improve the quality of the crystal has become a technical problem that needs to be solved urgently.

[0004] In a high-temperature furnace at 1800℃ (the melting point of gallium oxide), conventional methods such as physical stirring and ultrasonic treatment cannot be achieved. Although increasing the temperature can reduce the viscosity of the melt and improve its flowability, the higher the temperature, the more significant the volatilization and decomposition of gallium oxide, and the corrosion process of the crucible is accelerated. Sometimes the bubbles at the bottom of the crucible increase, leading to unstable crystal growth interface.

[0005] Chinese patent CN202210482935.2 (Invention name: A raw material doping method for changing the fluidity of gallium oxide melt) discloses a method: by forming a solution with elemental Ga and hydrochloric acid, then doping, drying and oxidizing, using alkali metals such as Li, Na and K to improve the flowability of the gallium oxide melt, thereby expelling the gas in the raw material and eliminating the pores in the crystal. However, this method is relatively complex, with many process steps. Although the segregation coefficients of alkali metals in the gallium oxide melt are low, trace amounts of alkali metals may still remain, and the oxidation and crushing steps can easily lead to contamination of the gallium oxide. In addition, the introduction of alkali metals may change the chemical equilibrium of the melt, affect the intrinsic defect concentration of the crystal, and thus degrade the device performance.

[0006] Therefore, there is an urgent need for a method for removing bubbles in a gallium oxide high-temperature melt that is more efficient, economical, and does not cause pollution to raw materials during the preparation process. SUMMARY

[0007] To solve the above at least one technical problem, the present application provides a method for removing bubbles in a gallium oxide high-temperature melt that is efficient, economical, and does not cause pollution to gallium oxide raw materials. On the one hand, the sintering process after pressing forming is used to minimize the residual gas in the raw materials, and on the other hand, the process control during the melt holding process, such as acceleration, deceleration, and reverse rotation, is used to achieve the removal of bubbles. Through this method, it is expected to significantly reduce the number of bubbles in the gallium oxide crystal and improve the overall quality of the crystal, thereby meeting the high requirements of high-performance electronic devices for gallium oxide materials.

[0008] According to one aspect of the present application, a method for removing bubbles in a gallium oxide melt is provided, the method comprising the following steps: Step (1), raw material pretreatment, selecting β-gallium oxide powder with a purity of ≥99.999%, placing it in a mold, and uniformly pressing at a pressure of 100-300 MPa for a holding time of 2 minutes or more to press the gallium oxide powder into a shape. The pressing pressure and holding time are precisely controlled to make the powder particles tightly bonded to form a compact and uniform green body.

[0009] Step (2), segmented sintering treatment, placing the pressed gallium oxide green body in a sintering furnace, first performing low-temperature preliminary sintering at a temperature not higher than 1000°C, then heating to a temperature range of 1500-1700°C for high-temperature sintering to obtain a dense gallium oxide sintered body.

[0010] Step (3), melt stirring control, placing the gallium oxide sintered body in a crucible for melting and crystal growth. During the melt holding stage, the crucible rotation is controlled according to the pre-set crucible dynamic rotation mechanism, which includes the alternating cycle of clockwise acceleration and counterclockwise deceleration, with a speed range of 5-30 rpm and a cycle number of 2 times or more. By precisely controlling the rotation parameters of the crucible, a uniform temperature field and flow field are formed inside the melt, promoting the aggregation and floating of bubbles.

[0011] In one embodiment of the present application, in step (1), the average particle size D of the β-gallium oxide is 4.5 μm or less, or 4 μm or less.

[0012] In another embodiment of the present application, in step (1), a hot isostatic pressing forming process is used to press the gallium oxide powder into a shape.

[0013] In one embodiment of the present application, in step (2), the low-temperature preliminary sintering is performed in an air environment, with a heating rate of 5-10℃ / min and a holding time of 2-10h; and the high-temperature sintering is performed in an air environment, with a heating rate of 1-5℃ / min and a holding time of 2-10h.

[0014] In another embodiment of the present application, in step (2), the sintering of the gallium oxide body is performed by a microwave sintering method.

[0015] In one embodiment of the present application, in step (3), in a single cycle, the rotating direction is first changed to clockwise rotation at a predetermined acceleration to 10-30r / min, and maintained for a first rotation time, and then changed to counterclockwise rotation at a predetermined deceleration to 5-15r / min, and maintained for a second rotation time, and the sum of the first rotation time and the second rotation time is not less than 30 minutes.

[0016] In another embodiment of the present application, in step (3), the dynamic rotation further comprises, after the clockwise acceleration, a stop, and then a counterclockwise deceleration, and a single cycle period is 30-90 minutes.

[0017] In another embodiment of the present application, in step (3), an external physical field, such as a magnetic field or an electric field, can be introduced to assist the removal of the bubbles. These external physical fields can affect the fluidity of the melt and the movement trajectory of the bubbles, and promote the aggregation and floating of the bubbles, thereby improving the bubble removal efficiency.

[0018] In another embodiment of the present application, step (4) is further included, and in the crystal growth process of step (4), the rotating speed of the crystal is V1, the crystal growth rate is V2, the axial temperature gradient of the melt is G, the product V1×G of the rotating speed V1 and the axial temperature gradient G of the melt is controlled to be not more than 350, the surface of the melt is substantially horizontal or concave to the center of the melt, and the product V2×G of the crystal growth rate V2 and the axial temperature gradient G of the melt is controlled to be not more than 35, wherein the value range of V1 is 1-15rpm, the value range of V2 is 0.5-5mm / h, and the value range of G is 5-70℃ / cm.

[0019] According to another aspect of the present application, a crystal growth device for removing bubbles in a gallium oxide melt is further provided, and the crystal growth device is equipped with a crucible speed control rotating system for performing a programmable rotating drive on the crucible, and is adapted to a composite rotating mode of clockwise acceleration and counterclockwise deceleration. A temperature measuring device, which comprises an infrared thermometer or a thermocouple, is used to realize the synchronous monitoring of temperature and interface state; and a temperature measuring-control linkage system links the temperature measuring device with the heating system and the crucible speed control rotation system of the crystal growing equipment, and when the temperature measuring device detects temperature abnormality, the system automatically triggers adjustment instructions to adjust the heating power or change the crucible rotation speed.

[0020] In one embodiment of the present application, the crystal growing equipment for removing bubbles in gallium oxide melt is also equipped with an annular gradient temperature control heat shield which surrounds the outside of the crucible to make the axial temperature gradient of the crucible uniform and stable.

[0021] According to another aspect of the present application, a beta-Ga2O3 single crystal is provided, which can be prepared according to the method of any one of the embodiments of the first aspect. The bubble removal rate of the beta-gallium oxide single crystal is greater than or equal to 90%, and the radial deviation of the resistivity is less than or equal to 3%.

[0022] According to still another aspect of the present application, a power device based on the beta-Ga2O3 single crystal is also provided, including but not limited to a field effect transistor, a diode or a deep ultraviolet light detector. According to the present application, since the power device adopts the above-mentioned tin-doped Ga2O3 single crystal thin film as the core material, it exhibits excellent electrical properties and reliability, and is suitable for next-generation power electronic and optoelectronic application fields.

[0023] Compared with the prior art, the present application has the following beneficial effects: According to the method, three process links of raw material pretreatment, staged sintering and melt stirring are cooperatively controlled, three main bubble sources of volatile impurities / adsorbed gas in the raw material, thermal decomposition in the growth process and gas wrapping at the solid-liquid interface are solved, the bubbles in the melt can be basically eliminated, and the crystal transparency is significantly improved. The bubble removal rate of the obtained beta-gallium oxide single crystal is greater than or equal to 90%, and the resistivity radial deviation is less than or equal to 3%. By optimizing the pressing process, combining the purity and particle size control of gallium oxide, the voids between the gallium oxide raw material powders are effectively reduced, the content of residual gas in the pressed body is reduced, favorable conditions are created for further discharge of gas in the subsequent sintering process, and the quality of the final gallium oxide crystal is ensured. According to the staged sintering method, the body is first pre-sintered at a lower temperature to volatilize the organic matter and moisture in the body, the powder particles are preliminarily combined, the residual gas in the body is further discharged, and the defects caused by rapid gas escape during subsequent high-temperature sintering are reduced. Then, the temperature is increased to a higher temperature for main sintering, so that the powder particles are fully diffused and combined, a more dense structure is formed, the strength and density of the body are further improved, a high-quality body basis is provided for the subsequent crystal growth process, and the performance of the final gallium oxide crystal is ensured. The application also creatively proposes that the dynamic rotation mechanism for the crucible can effectively reduce the generation of bubbles and quickly remove the small bubbles generated in the melt. By accelerating clockwise rotation and then decelerating counterclockwise rotation, a strong shear flow can be generated by changing the direction of rotation to destroy the bubble adhesion interface and promote the merging and floating of small bubbles. In addition, the alternating speed can also avoid the crystal defects caused by melt turbulence. In addition, combined with appropriate holding time, the bubbles have enough time to escape from the melt, thereby effectively reducing the bubble content in the gallium oxide melt and improving the growth quality and performance stability of the crystal. The above description is only a summary of the technical solutions of the embodiments of the application. In order to more clearly understand the technical means of the embodiments of the application, the embodiments of the application can be implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the embodiments of the application more obvious and easy to understand, the specific implementation of the embodiments of the application is described below. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the description of the embodiments of the present application will be briefly introduced. Obviously, the drawings in the following description are only some example embodiments of the present application. Those skilled in the art can obtain other drawings according to the content of the example embodiments of the present application and these drawings without creating any creative labor.

[0025] Figure 1 is a flowchart of an embodiment of the present application. Figure 1The shown process includes raw material pretreatment, segmented sintering, and crucible rotation control.

[0026] Figure 2 is a process schematic of another embodiment of the present application. Figure 2 The shown process includes raw material pretreatment, segmented sintering, crucible rotation control, and process parameter control during crystal growth.

[0027] Figure 3 is a single crystal growth apparatus for removing bubbles in a gallium oxide melt in an embodiment of the present application, comprising a crystal growth apparatus, a crucible speed control rotation system, a temperature measuring device, and the like. Among them: 1-crystal growth apparatus, 2-crucible, 3-melt, 4-crucible bottom support, 5-apparatus base, 6-temperature measuring device, 7-metal cover, 8-furnace lining, 9-heating system, 10-annular temperature control heat shield, 11-crucible speed control rotation system, 12-heat insulation baffle.

[0028] Figure 4 is a schematic diagram of the resistivity radial deviation sampling position of a gallium oxide single crystal in an embodiment of the present application. A number of test points are selected radially outward from the center of the single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible for resistivity radial deviation testing. The test results show that the resistivity radial deviation of the gallium oxide single crystal is less than or equal to 3%. Detailed description of the invention The present application will be further described below in conjunction with the accompanying drawings and examples. It can be understood that the specific examples described herein are only used to explain the present application, and are not limiting of the present application. Those skilled in the art can understand that in the various embodiments of the present application, many technical details are presented in order to enable the reader to better understand the present application. However, the claimed technical solutions of the present application can be realized even without these technical details and various changes and modifications based on the following embodiments.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In the case of conflict between any document incorporated by reference and the present specification, the present specification will control.

[0031] Unless otherwise indicated, "including", "comprising", "having", "containing", and the like, as used herein, are meant to be open-ended terms that are to be interpreted in the context of this application. They are not intended to exclude or to otherwise limit other features, elements, components, materials, steps, acts, or the like.

[0032] It should be understood that for numerical ranges in the present application, it is intended that every numerical value within the range is also specifically disclosed. DETAILED DESCRIPTION

[0033] Reference is made to Figure 1 , Figure 1 A flow chart of the method for removing bubbles in Ga2O3 melt is shown in detail. The method comprises the following steps: Step (1), raw material pretreatment, select β-gallium oxide powder with purity ≥ 99.999%, place in the mold at a uniform speed, control the pressing pressure to be 100-300 MPa, and the pressure holding time to be more than 2 min, press the gallium oxide powder into shape. Accurately control the pressing pressure and pressure holding time to make the powder particles tightly combined to form a compact structure and a good uniformity of the green body.

[0034] In the present application, ultra-high purity Ga2O3 powder is used as the starting raw material. Metal or non-metal impurities contained in low-purity raw materials, such as SiO2, CuO, etc., may decompose at high temperature and release gas. These gases are difficult to escape during high-temperature melting and are extremely easy to form bubbles and be wrapped into the crystal. By selecting β-gallium oxide powder with purity ≥ 99.999%, the gas source introduced by impurities can be significantly reduced, thereby effectively inhibiting bubble generation. At the same time, high-purity raw materials help to improve the electrical uniformity and structural integrity of the final single crystal, laying a foundation for the subsequent growth of high-quality gallium oxide single crystals. In addition, in order to ensure the consistency of each batch of raw materials, all batches of β-gallium oxide powder need to be detected by ICP-MS to confirm that the impurity content meets the standard before use, or use GDMS and other means to analyze the trace elements of each batch of raw materials.

[0035] The average particle size D of β-gallium oxide is preferably 5 μm or less, or 4.5 μm or less, or 4 μm or less. The particle size of the raw material determines the density of the pressed gallium oxide green body. The smaller the particle size, the smaller the gap between the powder, and the less gas contained in the green body. Therefore, controlling the particle size of the raw material not only helps to improve the density of the green body, but also effectively reduces the residual gas trapped in the interstitial gap during the pressing process. In the subsequent heating process, smaller pores are more easily removed by diffusion mechanism, reducing the probability of stable bubble formation in the melt. At the same time, fine and uniform particle distribution is conducive to the uniform transmission of thermal field and stress field, avoiding the generation of bubbles caused by local overheating or uneven melting. Combined with the dual advantages of high purity and ultra-fine particle size, the generation of bubble defects can be significantly inhibited from the source.

[0036] WC hard alloy die can be used during pressing, the surface roughness Ra of the die is 0.1 μm, and a very small surface roughness is also beneficial to the formation of a dense structure of gallium oxide powder. A segmented elastic die can also be used, and the pressing forces of the upper and lower dies are independently controlled. The pressing mode is one-way pressing or two-way pressing. When one-stage pressing is used, the pressing rate is 5-10 MPa / s, the pressing is stopped after the desired pressing pressure is reached, and the pressure is maintained for a predetermined time, for example, 4 minutes, 8 minutes, 10 minutes, 12 minutes, etc., and the minimum time is not less than 2 minutes. When segmented pressing is used, the pressing rate is unchanged, the pressure can be pre-pressed at a lower pressure for a certain time, and then the pressure is increased to a higher pressure for pressure maintenance. The pre-pressing pressure is usually 30%-50% of the final pressure, and the pressure maintenance time is 30-120 seconds, so as to discharge the air between the powders and achieve preliminary densification. The pressure range of the main pressing stage is 100-300 MPa, and the pressure maintenance time is not less than 4 minutes, so as to ensure that the density of the compact reaches more than 60% of the theoretical density. The pressure is increased by 10% from the center to the edge in a gradient manner, so as to reduce the cracks and delamination defects caused by stress concentration at the edges and corners. At the same time, after the pressure maintenance is completed, a stepwise pressure relief process is used, the pressure is reduced by 30-50 MPa at each level and maintained for 30 seconds, so as to avoid the cracking of the compact caused by elastic aftereffect. The obtained gallium oxide green compact has high density, low porosity and good mechanical strength, which provides a structural guarantee for subsequent cold isostatic pressing or direct hot pressing sintering.

[0037] The entire pressing process can be carried out at room temperature in an air atmosphere, and the environmental humidity should be ≤30%. The gallium oxide compact obtained by pressing is in a cylindrical shape, and the radial and axial shrinkage rates are both less than 1.5%, without cracks, delamination or obvious defects, and the density of the compact is controlled to be more than 85% of the theoretical density, so as to ensure that there is no residual porosity in the subsequent melting process.

[0038] In the method of the application, the gallium oxide powder can also be pretreated by using a hot isostatic pressing forming process. Hot isostatic pressing sintering can make the powder material achieve more sufficient densification under the combined action of high temperature and high pressure, effectively eliminate the pores and other defects in the material, and thus improve the quality of the gallium oxide crystal. For example, in the hot isostatic pressing process, the temperature is usually controlled to be 800-1200℃, the pressure is 100-200 MPa, and the pressure maintenance time is not less than 30 minutes. The atomic diffusion rate is accelerated at high temperature, and the isotropic high pressure action can significantly promote the grain boundary fusion and pore annihilation. A program-controlled temperature should be used in the cooling stage to avoid the accumulation of thermal stress and cause cracking. Through strict control of the process parameters, the density of the finally obtained compact can be close to more than 98% of the theoretical density. The hot isostatic pressing sintering equipment is expensive, the operation is complex, the requirements are extremely strict, the cost is high, and the time is long, so the hot isostatic pressing process is more suitable for the preparation of high-value-added and high-performance gallium oxide single crystals. In order to balance the cost and performance, a combined process path of cold isostatic pressing preforming combined with subsequent vacuum sintering can be used to achieve near-densification at a lower cost.

[0039] Step (2), the segment sintering treatment, the pressed shaped gallium oxide blank is placed in a sintering furnace, first low-temperature pre-sintering at a temperature not higher than 1000℃, then high-temperature sintering at a temperature range of 1500-1700℃ to obtain a dense gallium oxide sintered body.

[0040] The prior art gallium oxide sintering generally adopts one-step sintering, in order to further remove the volatile impurities and / or adsorbed gas contained in the raw material gallium oxide powder, a relatively long time of calcination is needed before the gallium oxide blank is placed into the growth furnace, and the one-step sintering is extremely prone to problems such as wrapping, powder agglomeration, etc. Therefore, the present application proposes a segment sintering scheme on the basis of the traditional one-step sintering process. At the same time, by controlling the heating rate and holding time, the grain boundary structure is further optimized, and the material density is improved.

[0041] First, pre-sintering at a relatively low temperature, the sintering atmosphere can be an oxygen-containing atmosphere, such as air, the purpose is to volatilize the organic matter and moisture in the blank, rather than densification. Therefore, the heating rate of the low-temperature pre-sintering stage is relatively slow, so that the gas can have enough time to slowly diffuse from the inside of the blank to the surface and be carried away by the flowing atmosphere. Generally speaking, the thicker the blank, the longer the path for the internal gas to diffuse outward, the greater the resistance, and if the heating rate is too fast, it will cause internal pressure accumulation, resulting in cracking, bubbling, etc. However, the heating rate of the low-temperature pre-sintering stage should not be too slow, otherwise it will lead to high time cost. For example, the heating rate of the low-temperature pre-sintering can be 5℃ / min or more, or 5-10℃ / min, or 5-8℃ / min, and the holding time can be 2-10 h, to ensure that the physically adsorbed moisture (H2O) and chemically combined hydroxyl (-OH) in the gallium oxide raw material can be basically removed.

[0042] Subsequently, the temperature is raised to a higher temperature for main sintering, the sintering atmosphere is preferably a protective atmosphere, such as argon or nitrogen, and the purity of the protective gas is ≥99.99%. At the same time, in order to inhibit the high-temperature decomposition of gallium oxide, sometimes oxygen atmosphere needs to be introduced, at this time the oxygen partial pressure can be 10 -2Pa. The heating rate of the high-temperature sintering stage is 1-5°C / min, or 1-3°C / min, or 3-5°C / min, and the holding time is controlled to be 2-10 h to ensure that the grains grow sufficiently and reduce internal stress. Considering the heating capacity of the sintering furnace itself, the heating rate of the high-temperature sintering stage can be slightly lower than that of the low-temperature initial sintering stage, which is conducive to inhibiting abnormal grain growth and obtaining a microstructure with small grains and high density. However, if the heating is too slow, the grains will have too much growth time, leading to grain coarsening. In turn, the coarse grains will wrap the pores, making it difficult for the pores to escape. By controlling the temperature in stages, the thermal shock of the green body during sintering is effectively alleviated, and the formation of microcracks and pores is inhibited. Further, the strength and density of the green body are improved, providing a high-quality green body basis for the subsequent crystal growth process, thereby ensuring the performance of the final gallium oxide crystal.

[0043] In the embodiments of the present application, more heating stages can also be included to achieve gradient pre-sintering of the raw material. Optionally, the first heating stage is at room temperature-600°C for 1-2 h to remove physically adsorbed water and organic matter, preventing the generation of bubbles or cracks during the subsequent melting process; the second heating stage is heated to 600-1100°C for 2-4 h to strengthen the volatilization of low-boiling-point impurities (such as C, H); the third stage is to raise the furnace temperature to 1200-1400°C, and after the temperature is constant, it is held for 2-4 h to quickly pass through the medium-low temperature zone and inhibit Ga2O3 grain coarsening; the fourth stage continues to heat to 1500-1700°C and is held for 2-10 h for high-temperature sintering to promote the densification and grain growth between the particles, forming a Ga2O3 sintered body with high density and low defects. The heating rate of each stage is controlled to be 1-15°C / min to avoid powder caking or uneven reaction due to thermal shock. Those skilled in the art can adjust the heating stages according to actual production needs. The multi-stage heating design can effectively improve the density and structural uniformity of the sintered body, significantly reduce the grain boundary defect density, and the sintered body density can reach more than 95%. This process is particularly suitable for the preparation of large-size, high-quality gallium oxide single crystal growth precursors, providing reliable blank protection for the subsequent growth of large-size crystals by the Czochralski method or the vertical Bridgman method.

[0044] In the method of the present application, microwave sintering and other calcination methods can also be used to sinter the gallium oxide green body. Microwave sintering utilizes the direct interaction between microwaves and the gallium oxide green body to heat the entire sintered body to the sintering temperature, which has the advantages of fast heating speed and uniform heating. This sintering method can reduce thermal stress during sintering and avoid defects caused by rapid gas escape due to local overheating, thereby more effectively reducing the amount of gas remaining in the sintered body.

[0045] Step (3), melt stirring control, the gallium oxide sintered body is placed in a crucible, and melting and crystal growth are performed. In the melt holding stage, the crucible rotation is controlled according to a pre-set crucible dynamic rotation mechanism. The dynamic rotation includes an alternating cycle of clockwise acceleration and counterclockwise deceleration, and the rate ranges from 5 rpm to 30 rpm, and the cycle number is 2 or more. By accurately controlling the rotation parameters of the crucible, a uniform temperature field and flow field are formed in the melt, which promotes the aggregation and floating of bubbles.

[0046] The inventors of the present application creatively propose that the generation of bubbles can be effectively reduced and the small bubbles generated in the melt can be quickly removed by setting a dynamic rotation mechanism for the crucible. By first rotating clockwise at a high speed and then rotating counterclockwise at a low speed, a strong shear flow can be generated by changing the direction of rotation to destroy the bubble adhesion interface and promote the merging and floating of small bubbles. At the same time, the alternating speed can also avoid the crystal defects caused by melt turbulence. In addition, combined with appropriate holding time, for example, the single cycle period is not less than 30 minutes, or even not less than 1 hour, to ensure that the bubbles have enough time to escape from the melt, thereby effectively reducing the bubble content in the gallium oxide melt and improving the growth quality and performance stability of the crystal. After the crystal growth is completed, the crystal is cooled to room temperature and taken out, and a gallium oxide single crystal ingot is obtained.

[0047] In the embodiment of the present application, the predetermined acceleration is used to rotate clockwise at a speed of 10-30 r / min for a first rotation time, and then the predetermined deceleration is used to rotate counterclockwise to a speed of 5-15 r / min for a second rotation time. The sum of the first rotation time and the second rotation time is not less than 30 minutes. The dynamic rotation process can be repeated 2-4 times to ensure that the bubbles in the melt are fully floated and discharged. By controlling the acceleration and deceleration within the range of 0.5 rpm / s, the instability of the melt caused by violent disturbance is avoided. At the same time, the timing of switching the rotation direction is matched with the holding stage, which is beneficial to maintaining the uniformity of the temperature gradient and reducing the disturbance of the crystal growth interface. Experiments show that the gallium oxide single crystal obtained by using the stirring method has a bubble density reduced by more than 60% compared with the traditional process, and the transmittance is significantly improved, which meets the demand of high-end power devices for high-quality substrates.

[0048] According to the preparation process of the present application, the dynamic rotation further includes stopping rotation for a period of time after the clockwise acceleration, and then performing counterclockwise deceleration, and the single cycle period is 30-90 minutes. The stopping stage helps to eliminate the residual shear flow in the melt, so that the bubbles further aggregate and grow without external disturbance, and the floating efficiency is improved. Combined with the complete thermal cycle design, the disturbance of thermal convection caused by continuous rotation is effectively avoided, and the stability of the crystal growth interface is ensured.

[0049] In other embodiments of the present application, in step (3), an external physical field, such as a magnetic field or an electric field, is introduced to assist the removal of the bubbles. These external physical fields can affect the fluidity of the melt and the trajectory of the bubbles, promoting the aggregation and floating of the bubbles, thereby improving the removal efficiency. Among them, the application of an alternating magnetic field can induce the melt to generate a Lorentz force, driving the directional migration of the micro-bubbles; while the electrostatic field makes the bubbles move to the low field strength area through the dielectrophoresis effect, avoiding their aggregation at the crystal growth interface. The external physical field and the dynamic rotation work together to further strengthen the detachment and transport process of the bubbles, significantly improving the removal efficiency.

[0050] In the method for removing bubbles in a gallium oxide melt according to the present application, the cooling process of the sintered body, as the final link of the sintering process, also has an important influence on the sintering effect. If not controlled, it may eventually lead to cracking, excessive grain growth, and insufficient release of thermal stress, which affect the quality of the crystal. Generally, after high-temperature sintering is completed, the sintered body is slowly cooled to room temperature with the furnace at a cooling rate of 3-10 ℃ / min. This cooling rate is directly related to factors such as the size, thickness of the green body, and uniformity of the thermal field in the furnace. For example, the thicker the green body, the slower the cooling rate. In the embodiments of the present application, a segmented cooling method can be used. At a high temperature above 1000℃, a relatively high cooling rate of 3-5 ℃ / min is used to quickly cool down to inhibit grain growth. Subsequently, in the brittle temperature zone of 600-1000℃, a relatively low cooling rate of 1-2 ℃ / min or even lower is used to very slowly cool down to release thermal stress and prevent cracking. In the low temperature zone below 600℃, the risk of thermal stress is reduced, and the cooling rate can be increased to improve efficiency. For example, the cooling rate can be 5-10 ℃ / min to continue to cool down to room temperature.

[0051] In summary, according to the method of the present application, through the synergistic control of the three process links of raw material pretreatment, segmented sintering, and melt stirring control, the three most important bubble sources of volatile impurities / adsorbed gases in the raw material, thermal decomposition during growth, and gas inclusion at the solid-liquid interface are solved. The bubbles in the melt can be basically eliminated, and the transparency of the crystal is significantly improved. The final β-gallium oxide single crystal has a bubble removal rate of ≥90% and a resistivity radial deviation of ≤3%.

[0052] Referring to Figure 2 , Figure 2The method further comprises the following step: step (4) crystal growth, in the crystal growth process of step (4), the crystal rotation speed is V1, the crystal growth rate is V2, the melt axial temperature gradient is G, the product V1xG of the rotation speed V1 and the melt axial temperature gradient is controlled to be not more than 350, the melt surface is substantially horizontal or concave to the melt center, and the product V2xG of the crystal growth rate V2 and the melt axial temperature gradient G is controlled to be not more than 35, wherein the value range of V1 is 1-15 rpm, the value range of V2 is 0.5-5 mm / h, and the value range of G is 5-70 ℃ / cm.

[0053] The crystal growth process parameters are another key to reduce or control the formation of bubbles, and the main process parameters include the crystal rotation speed V1, the crystal growth rate V2 and the melt axial temperature gradient G.

[0054] The crystal rotation speed V1 is a key process parameter that needs to be concerned, and appropriate crystal rotation can stir the melt, make the melt temperature and composition more uniform, and also change the local flow field at the solid-liquid interface, which helps to "sweep" small bubbles near the interface to the edge of the crystal and prevent them from being captured. However, the crystal rotation rate V1 should not be too fast, otherwise it will introduce strong forced melt convection, which may bring temperature fluctuations and even gas entrainment.

[0055] Precise control of the temperature field and temperature gradient G is an important technical means to exclude bubbles in the melt. By designing a reasonable thermal field, the axial temperature gradient G at the solid-liquid interface can be ensured to be moderate, uniform and stable. A too large temperature gradient will cause component undercooling, so that bubbles or other impurities are quickly captured into the crystal; a too small temperature gradient may make the interface unstable. In actual production, by optimizing the thermal field, the solid-liquid interface is made as flat as possible or slightly concave to the melt. This is conducive to bubbles to have enough time and path to be expelled to the side of the crystal when they are formed or close to the interface, rather than being wrapped into the interior of the crystal. An interface concave to the melt is most likely to capture bubbles.

[0056] The crystal growth rate V2 is another key parameter. Reducing the growth rate is one of the most effective methods to reduce bubble defects. According to the component undercooling theory, the critical growth rate Vc is proportional to the temperature gradient G. When the actual growth rate V2 is less than Vc, stable planar growth can be maintained to avoid the wrapping of bubbles and impurities. For gallium oxide, a relatively slow growth rate is usually adopted, for example, 0.5-5 mm / h, or 0.8-4 mm / h, or even 1-3 mm / h, to ensure that the solid-liquid interface advances stably and gives bubbles enough time to escape.

[0057] In step (4) of the present application, the crystal growth process can be carried out under a suitable atmosphere, and the commonly used growth atmosphere includes air, oxygen and the like, or a mixture of the same with inert gas. Oxygen atmosphere helps to inhibit the decomposition of Ga2O3 at high temperature (reaction: Ga2O3(s) → Ga2O(g) + O2(g)). In an environment with high oxygen partial pressure, the decomposition reaction is inhibited, thereby reducing the generation of bubbles (mainly Ga2O vapor) from the source. Higher pressure can significantly increase the decomposition temperature of Ga2O3, so that it does not decompose substantially below the melting point (~1800°C).

[0058] Referring to Figure 3 , Figure 3 is a schematic view of a crystal growth apparatus structure for removing bubbles in a gallium oxide melt in an embodiment of the present application. Figure 3 The crystal growth apparatus 1 shown is equipped with a crucible speed control rotation system 11 for performing a programmable rotation drive on the crucible 2, and is adapted to a composite rotation mode of clockwise acceleration and counterclockwise deceleration. A temperature measuring device 6 including an infrared thermometer and / or a thermocouple is used to realize synchronous monitoring of temperature and interface state, and an observation-control linkage system links the observation device, the temperature measuring device 6 and the heating system 9 and the crucible rotation system 11 of the crystal growth apparatus 1. When the observation device observes an increase in bubbles, or the temperature measuring device 6 detects an abnormal interface temperature gradient, the system automatically triggers an adjustment instruction to adjust the heating power and change the crucible rotation speed, so as to timely suppress bubble generation.

[0059] In order to obtain β-gallium oxide single crystals substantially free of bubbles, in addition to comprehensive regulation and control at each process link, the use of crystal growth apparatus is also very important. The melt 3 is most directly contacted by the crucible 2, and a crucible 2 with small reaction with Ga2O3 melt and no introduction of impurities is generally used. It is necessary to ensure that the inner wall of the crucible 2 is smooth and clean, and any rough point can become a nucleation point for bubbles.

[0060] The uneven heating, crucible loss, etc. can cause gallium oxide to decompose or produce impurity gas, and the heating system needs to be improved and matched with special auxiliary equipment to strengthen the bubble discharge effect. For example, the heating device can be improved, a double heating structure is adopted, one is responsible for heating the raw materials in the crucible, and the other controls the temperature at the bottom of the crucible to avoid local overheating causing excessive decomposition of gallium oxide; at the same time, a gradient temperature control system is matched to accurately control the heating rate, for example, the temperature is slowly raised at 5℃ / min in the low temperature stage, so that the gas in the raw materials is gradually precipitated, and the sudden bubble is reduced. In other embodiments, a crucible isolation and flow guide device can also be installed, a partition wall and a sealing screen are arranged in the crucible to form an independent feeding cavity, and a corresponding automatic feeding device is matched, the raw materials are preheated and melted in the feeding cavity, and then smoothly flow into the crystallization zone through the flow guide structure to avoid direct feeding to cause disturbance of the melt to produce bubbles; a special oxygen delivery device can also be connected to the feeding cavity to control the oxygen content to inhibit the decomposition of gallium oxide to produce gas. A rotary shaking gas driving device can also be configured, a driving device integrating rotation and swing is designed for the crucible, the driving device is driven by the meshing transmission of the driving bevel gear and the driven bevel gear to make the crucible rotate and swing in three dimensions, and the vortex effect is used to "squeeze out" the bubbles to the surface of the melt; at the same time, a heat insulation layer is added to the device to delay the cooling rate of the melt and reserve sufficient time to exhaust the bubbles.

[0061] In an embodiment of the present application, the gallium oxide melt bubble removing crystal growing device is also equipped with an annular temperature control heat shield 10, which surrounds the outside of the crucible to make the axial temperature gradient of the crucible uniform and stable, further reducing the thermal disturbance of the crystal growth interface, thereby improving the crystallization quality and interface stability. By optimizing the heat shield material and cooling rate, the system stability and repeatability are further improved to ensure the consistency of each batch of crystal growth process. For example, the heat shield material is selected from high-purity zirconia, which has excellent high-temperature resistance and low heat radiation absorption rate, can maintain stable heat performance in a long time of operation, and further ensures the uniformity and controllability of the crystal growth environment.

[0062] In addition, a tail gas purification and recovery device can also be installed on the crystal growing device of the present application, a condensation recovery module is arranged on the tail gas discharge path to recover the metal gallium vapor in the tail gas to avoid its backflow pollution to the melt to produce bubbles; at the same time, a gas filtering device is matched to prevent impurity particles in the tail gas from entering the growth cavity to reduce the pollution gas.

[0063] Figure 4 The resistivity radial deviation sampling position diagram of the gallium oxide single crystal in the embodiment of the present application is shown, a plurality of test points are selected along the radial direction outward from the center of the single crystal at the heights of 0 mm, 10 mm and 20 mm from the bottom of the crucible, and the resistivity radial deviation test is performed. The test results show that the resistivity radial deviation of the gallium oxide single crystal is less than or equal to 3%.

[0064] The power device based on the tin-doped Ga2O3 single crystal according to the present application includes, but is not limited to, a field effect transistor, a diode or a deep ultraviolet light detector. According to the present application, since the power device adopts the tin-doped Ga2O3 single crystal thin film as a core material, excellent electrical performance and reliability are exhibited, and the power device is suitable for next-generation power electronic and optoelectronic application fields.

[0065] Example 1 The present embodiment adopts the crystal growth equipment as shown in Figure 3 The present embodiment adopts the crystal growth equipment as shown in Figure 1 The method for removing bubbles in a gallium oxide melt includes the following steps: (1) A raw material pretreatment step. Select β-gallium oxide powder with a purity of ≥99.999%, and an average particle size D of 4.5 μm. The gallium oxide powder is uniformly pressed in a mold, a WC hard alloy mold is used, the surface roughness Ra of the mold is 0.1 μm, the pressing pressure is controlled to be 200 MPa, the pressure holding time is 8 minutes, and the gallium oxide powder is pressed into a shape at room temperature (25°C). The pressing pressure and pressure holding time are accurately controlled to make the powder particles tightly combined to form a compact structure and a good uniformity green body. The green body density is 3.8 g / cm 3 , the porosity is ≤5%, and the inter-particle voids of the powder are uniformly distributed. The residual gas content is reduced to 0.3 vol% as measured by the helium replacement method.

[0066] (2) A step of sub-section sintering. The pressed gallium oxide green body is placed in a sintering furnace, and first heated to 900 ℃ at a heating rate of 5 ℃ / min in an air atmosphere, and then kept at this temperature for 3h for low-temperature preliminary sintering to remove adsorbed water, crystal water and trace amounts of organic matter and other impurities in the powder. Then, the atmosphere in the sintering furnace is changed to a mixed atmosphere of argon and oxygen, and the oxygen partial pressure is kept at 10 -2 Pa to inhibit the decomposition of gallium oxide. The temperature is raised to 1600 ℃ at a heating rate of 3 ℃ / min, and sintered for 5h for high-temperature sintering to ensure that the crystal grains grow sufficiently and reduce internal stress. After the sub-section sintering is completed, the sintered body is cooled to room temperature with the furnace to obtain a dense gallium oxide sintered body, and the sintered body density is increased to 96%.

[0067] (3) Crucible stirring control step. 480 g of gallium oxide sintered body was placed in a 2-inch alloy crucible with an inner diameter of about 55 mm, and crystal growth was performed. First, the temperature was raised to the gallium oxide melting temperature at a rate of 3 ℃ / min, and the temperature was maintained at 1810 ℃ for 3 h. During the melt holding stage, the crucible rotation was controlled according to the pre-set crucible dynamic rotation mechanism. The crucible was accelerated clockwise at an acceleration of 0.5 rpm / s to 15 rpm, maintained for 5 minutes; then decelerated counterclockwise at a deceleration of 0.3 rpm / s to 10 rpm, maintained for 30 minutes, and the cycle was repeated 3 times; by changing the direction of rotation, a strong shear flow was generated to destroy the bubble adhesion interface and promote the coalescence and upward floating of small bubbles, while the alternating speed avoided the crystal defects caused by melt turbulence. Then the temperature was lowered to 1805 ℃, and the crystal growth was carried out after 3 hours of holding.

[0068] According to the method of the present embodiment, a gallium oxide single crystal with a size of φ55mmx25mm was obtained, no fine bubbles were observed by microscope, and the bubble removal rate reached 92% by spectral analysis. According to the method of Figure 4 , the resistivity radial deviation of the gallium oxide single crystal obtained in Example 1 was tested. 3x9, a total of 27 test points were selected along the radial direction from the center of the single crystal to the outside at a height of 0 mm, 10 mm and 20 mm from the bottom of the crucible, and the resistivity radial deviation test was carried out. The test results are shown in Table 1, and the results show that the resistivity radial deviation of the gallium oxide single crystal is less than or equal to 3%.

[0069] Table 1

[0070] Example 1 controls the rotation parameters of the crucible accurately, forms a uniform temperature field and flow field inside the melt, promotes the aggregation and upward floating of bubbles, and the bubble density inside the gallium oxide single crystal is reduced by more than 60% compared with the traditional process, the light transmittance is significantly improved, and the demand for high-quality substrates for high-end power devices is met.

[0071] Example 2 The present embodiment uses Figure 3 a crystal growth apparatus, and provides a method for removing bubbles in a gallium oxide melt as shown in Figure 2 , which comprises the following steps: (1) Raw material pretreatment step. Select β-gallium oxide powder with a purity of ≥99.999%, and the average particle size D of the powder is 4.5 μm. A WC hard alloy die is used, and the surface roughness Ra of the die is 0.1 μm. After preheating the die to 60 ℃, the gallium oxide powder is uniformly pressed in the die at a controlled pressing pressure of 240 MPa, and the pressure holding time is 12 minutes. The green body density reaches 4.2 g / cm 3, porosity ≤ 2%, the powder particles gap uniform distribution. By helium replacement method shows that the residual gas content is reduced to 0.1 vol%.

[0072] (2) Subsection sintering step. The pressed shaped gallium oxide body is placed in a sintering furnace, and then the sintering furnace is subjected to vacuum treatment, and the vacuum degree can be 10 -2 Pa, and further remove the gas molecules adsorbed on the surface of the gallium oxide sintered body and the crucible wall. Subsequently, the temperature is raised to 950 ℃ at a temperature raising rate of 5-8 ℃ / min, and the temperature is kept for 5 h at this temperature, and low-temperature preliminary sintering is performed to remove the adsorbed water, crystal water in the powder and promote the volatilization of low-boiling-point organic impurities. Then the atmosphere in the sintering furnace is changed to a mixed atmosphere of argon and oxygen, and the oxygen partial pressure is kept at 10 -2 Pa to inhibit the decomposition of gallium oxide. The temperature is raised to a temperature range of 1600-1700 ℃ at a temperature raising rate of 3-5 ℃ / min, and the temperature is kept for 5 h, and high-temperature sintering is performed to ensure that the crystal grains grow sufficiently and reduce internal stress. After the subsection sintering is completed, the sintered body is cooled to room temperature with the furnace, and a dense gallium oxide sintered body is obtained, and the sintered body density is increased to 98%.

[0073] (3) Crucible stirring control step. The gallium oxide sintered body of 550 g is placed in a 2-inch alloy crucible with an inner diameter of about 55 mm, and melting and crystal growth are performed. First, the temperature is raised to the gallium oxide melting temperature at a temperature raising rate of 6-8 ℃ / min, and the temperature is kept for 3 h at 1810 ℃. During the melt temperature keeping stage, the crucible rotation is controlled according to the pre-set crucible dynamic rotation mechanism, the crucible is accelerated clockwise to 15 rpm at an acceleration of 0.5 rpm / s, and kept for 5 minutes; then decelerated counterclockwise to 10 rpm at a deceleration of 0.3 rpm / s, and kept for 30 minutes, and the cycle is repeated for 3 times; the strong shear flow is generated by the rotation in different directions, the bubble adhesion interface is destroyed, the small bubbles are combined and floated up, and at the same time, the crystal defects caused by melt turbulence are avoided by alternating speed.

[0074] (4) Crystal growth step. Then the temperature in the crystal growth furnace is lowered to 1805 ℃, and the temperature is kept for 3 hours, and crystal growth is performed. The axial temperature gradient and the crystal growth rate in the crystal growth stage affect the stability of the solid-liquid interface, prevent impurities or bubbles from being captured into the crystal, and cause bubble defects. According to the embodiment, the axial temperature gradient is controlled in the range of 50-60 ℃ / cm, and the crystal growth rate is controlled in the range of 0.9-1 mm / h, in which case the solid-liquid interface is relatively stable, and the bubbles generated in the melt can have sufficient time to dissipate to the side of the crystal. At the same time, the crystal rotation speed is controlled at 5 rpm, which also helps to "sweep" the small bubbles near the interface to the edge of the crystal, preventing them from being captured by the crystal.

[0075] According to the method of the embodiment, a gallium oxide single crystal with a size of φ55mm*30mm is obtained, no fine bubbles are observed by a microscope, and the bubble removal rate reaches 97% by spectral analysis. According to the method, the resistivity radial deviation of the gallium oxide single crystal obtained in Example 2 is tested. 3*9, i.e., 27 test points are selected radially outward from the center of the single crystal at a height of 0mm, 10mm and 20mm from the bottom of the crucible, respectively, to test the resistivity radial deviation. The test results show that the resistivity radial deviation of the gallium oxide single crystal is less than 3%. Figure 4 The resistivity radial deviation of the gallium oxide single crystal obtained in Example 2 is tested according to the method. 3*9, i.e., 27 test points are selected radially outward from the center of the single crystal at a height of 0mm, 10mm and 20mm from the bottom of the crucible, respectively, to test the resistivity radial deviation. The test results show that the resistivity radial deviation of the gallium oxide single crystal is less than 3%.

[0076] Example 2 controls the rotation parameters of the crucible accurately, so that a uniform temperature field and flow field are formed inside the melt, the aggregation and floating of bubbles are promoted, the bubble density inside the gallium oxide single crystal is greatly reduced, and the light transmittance is significantly improved, which meets the demand of high-end power devices for high-quality substrates.

[0077] Example 3 The embodiment adopts the crystal growth equipment as shown in Figure 3 , and provides a method for removing bubbles in a gallium oxide melt, as shown in Figure 2 , which comprises the following steps: (1) Raw material pretreatment step. Select β-gallium oxide powder with a purity of ≥99.999%, and an average particle size D of 4.5μm. A segmented elastic mold is adopted, the upper and lower mold pressures can be independently controlled, and the mold surface roughness Ra=0.1μm. The gallium oxide powder is placed in the mold, and in a room temperature environment, the air is kept dry (humidity ≤30%), first pre-press at a pressure of 200MPa for 2min, then press at a pressure of 240MPa for 5-8min, and the pressure is kept increasing by 10% from the center to the edge. The gallium oxide powder is pressed into shape. The green body density reaches 4.0g / cm 3 , the porosity is ≤1%, and the inter-particle voids of the powder are uniformly distributed, and the porosity is 3%. The determination by the helium replacement method shows that the residual gas content is reduced to 0.1vol%.

[0078] (2) Step of segmented sintering. The pressed gallium oxide green body is placed in a sintering furnace, first heated to 850℃ at a heating rate of 5-8℃ / min, and kept at this temperature for 6-8h for low-temperature preliminary sintering to remove adsorbed water, crystal water in the powder and promote the volatilization of low-boiling-point organic impurities. Then the atmosphere in the sintering furnace is changed to a mixed atmosphere of argon and oxygen, and the oxygen partial pressure is kept at 10 -2Pa to inhibit the decomposition of gallium oxide. High-temperature sintering is performed at a temperature in the range of 1600-1700°C at a temperature increasing rate of 2-4 ℃ / min for 4-6 h to ensure that the crystal grains grow sufficiently and the internal stress is reduced. After the completion of the stepwise sintering, the sintered body is slowly cooled to room temperature at a cooling rate of 5-8 ℃ / min to obtain a dense gallium oxide sintered body, and the sintered body density is increased to 97%.

[0079] (3) Crucible stirring control step. Gallium oxide sintered bodies totaling 500 g are placed in a 2-inch alloy crucible with an inner diameter of about 55 mm, and melt growth is performed. First, the temperature is increased to the gallium oxide melting temperature at a temperature increasing rate of 6-8 ℃ / min, and the temperature is maintained at 1810°C for 2 h. During the melt temperature maintaining stage, the crucible rotation is controlled according to the pre-set crucible dynamic rotation mechanism. The crucible is first accelerated clockwise to 12-15 rpm at an acceleration of 0.5 rpm / s, and maintained for 30 min. Then, the crucible rotation is stopped for 2 min to eliminate the residual shear flow in the melt, and to allow the bubbles to further grow without external disturbance, thereby improving the floating efficiency. Then, the crucible is accelerated counterclockwise to 8-10 rpm at an acceleration of 0.3 rpm / s, and maintained for 30 min, and the cycle is repeated 3 times. The pulse flow field generated by the alternating rotation breaks the bubble adhesion interface, promotes the merging and floating of small bubbles, and at the same time, avoids the crystal defects caused by melt turbulence by alternating the speed.

[0080] (4) Crystal growth step. Then, the temperature in the crystal growth furnace is decreased to 1805°C, and the temperature is maintained for 3 h to perform crystal growth. The axial temperature gradient and the crystal growth rate during the crystal growth stage affect the stability of the solid-liquid interface, and prevent impurities or bubbles from being captured in the crystal to cause bubble defects. According to the present embodiment, the axial temperature gradient is controlled in the range of 50-60 ℃ / cm, and the crystal growth rate is controlled in the range of 0.9-1 mm / h. In this case, it is observed that the solid-liquid interface is relatively stable, and the bubbles generated in the melt can have sufficient time to be dispersed to the side of the crystal. At the same time, the crystal rotation speed is controlled at 5 rpm, which also helps to "sweep" the small bubbles near the interface to the edge of the crystal, preventing them from being captured by the crystal. After the completion of the crystal growth, the temperature is maintained for 2.5 h to perform directional annealing to release the lattice stress and reduce the dislocation density.

[0081] According to the method of the present embodiment, a gallium oxide single crystal with a size of φ55 mm x 28 mm is obtained, no fine bubbles are observed by a microscope, and the bubble removal rate is 95% by spectral analysis. According to the method of the present embodiment, the gallium oxide single crystal has a size of φ55 mm x 28 mm, no fine bubbles are observed by a microscope, and the bubble removal rate is 95% by spectral analysis. Figure 4The method of Example 3, the resistivity radial deviation of the gallium oxide single crystal obtained in Example 3 was tested. 3x9, a total of 27 test points were selected along the center of the single crystal outward radially at the height of 0 mm, 10 mm and 20 mm from the bottom of the crucible, and the resistivity radial deviation test was performed. The test results show that the resistivity radial deviation of the gallium oxide single crystal is less than 3%.

[0082] Example 3 controls the rotation parameters of the crucible accurately, so that a uniform temperature field and flow field are formed inside the melt, the aggregation and floating of bubbles are promoted, the bubble density inside the gallium oxide single crystal is greatly reduced, and the light transmittance is significantly improved, which meets the demand of high-end power devices for high-quality substrates.

[0083] Example 4 Example 4 is similar to Example 1, except that the hot isostatic pressing forming technology is used to press the gallium oxide powder into a green body to be sintered. The specific implementation method is as follows: The β-gallium oxide powder with a purity of ≥99.999% is selected, and the average particle size D of the powder is 4.5 μm. A flexible isostatic pressing graphite mold is used as a pressing mold, and the surface roughness Ra of the mold is 0.1 μm. The gallium oxide powder is placed in the mold, the isostatic pressing cavity is kept in an inert atmosphere, the temperature is usually controlled at 800-1200℃, the pressure is 100-200 MPa, and the holding time is 30 minutes. The gallium oxide powder is pressed into a green body. In the hot isostatic pressing process, the atomic diffusion rate is accelerated at high temperature, combined with the isotropic high pressure effect, which can significantly promote the grain boundary fusion and pore annihilation. By strictly controlling the process parameters, the density of the green body obtained is about 5.76 g / cm 3 , close to 97% of the theoretical density, and the porosity is ≤0.3%. The determination by helium replacement method shows that the residual gas content is reduced to 0.05 vol%.

[0084] According to the method of the present embodiment, a gallium oxide single crystal with a size of φ55mmx25mm is obtained, no fine bubbles are observed by microscope, and the bubble removal rate is more than 97% by spectral analysis. According to the method of Figure 4 The method of Example 3, the resistivity radial deviation of the gallium oxide single crystal obtained in Example 3 was tested. 3x9, a total of 27 test points were selected along the center of the single crystal outward radially at the height of 0 mm, 10 mm and 20 mm from the bottom of the crucible, and the resistivity radial deviation test was performed. The test results show that the resistivity radial deviation of the gallium oxide single crystal is less than 3%.

[0085] In the embodiment 4, the gallium oxide blank is pressed by hot isostatic pressing technology, and a uniform temperature field and flow field are formed in the melt by precisely controlling the rotation parameters of the crucible, so as to promote the aggregation and floating of the bubbles, greatly reduce the bubble density in the gallium oxide single crystal, and significantly improve the light transmittance, thereby meeting the demand of high-end power devices for high-quality substrates.

[0086] Example 5 In the embodiment 5, the microwave sintering technology is used in the segmented sintering, which is similar to the embodiment 2. The specific implementation method is as follows. The pressed gallium oxide blank is placed in a sintering furnace, and then the sintering furnace is subjected to vacuum treatment, and the vacuum degree can be 10 -2 Pa, so as to further remove the gas molecules adsorbed on the surface of the gallium oxide sintered body and the crucible wall. Subsequently, the temperature is raised to 950 ℃ at a temperature raising rate of 8-10 ℃ / min, and the temperature is kept for 2 h, so as to perform low-temperature preliminary sintering, remove the adsorbed water and crystal water in the powder, and promote the volatilization of low-boiling-point organic impurities. Then, the atmosphere in the sintering furnace is changed into a mixed atmosphere of argon and oxygen, and the oxygen partial pressure is kept at 10 -2 Pa, so as to inhibit the decomposition of gallium oxide. The temperature is raised to a temperature range of 1600-1700 ℃ at a temperature raising rate of 3-5 ℃ / min, and the temperature is kept for 2 h, so as to perform high-temperature sintering, ensure the full growth of the grains, and reduce the internal stress. After the segmented sintering is completed, the sintered body is cooled to room temperature with the furnace, and a dense gallium oxide sintered body is obtained, and the sintered body density is increased to 98%.

[0087] According to the method of the embodiment, a gallium oxide single crystal with a size of φ55mm*30mm is obtained, no fine bubbles are observed by a microscope, and the bubble removal rate is more than 97% by spectral analysis. Figure 4 According to the method, the resistivity radial deviation of the gallium oxide single crystal obtained in the embodiment 5 is tested. 3*9, that is, 27 test points are selected radially outward from the center of the gallium oxide single crystal at a height of 0 mm, 10 mm and 20 mm from the bottom of the crucible, and the resistivity radial deviation is tested. The test results show that the resistivity radial deviation of the gallium oxide single crystal is less than 3%.

[0088] In the embodiment 5, the microwave segmented sintering method is used, and a uniform temperature field and flow field are formed in the melt by precisely controlling the rotation parameters of the crucible, so as to promote the aggregation and floating of the bubbles, greatly reduce the bubble density in the gallium oxide single crystal, and significantly improve the light transmittance, thereby meeting the demand of high-end power devices for high-quality substrates.

[0089] Comparative Example 1 To further verify the effectiveness of the present embodiment, the inventors designed a comparative experiment of Comparative Example 1. In Comparative Example 1, the pressing pressure was reduced to 20 MPa, the holding time was unchanged, and the other sintering and melt crystal growth processes and systems were the same as those of Example 1. The gallium oxide blank obtained in the raw material pretreatment step of Comparative Example 1 had a density of only 2.9 g / cm3, a porosity of up to 15%, and a residual gas content of up to 1.2 vol%, which was 4 times that of Example 1. The sintered body had a density of only 82%, and the internal residual pores had a size of 5-10 μm and a number of ≥20 / mm3. The final obtained gallium oxide crystal had a bubble removal rate of only 58%, and the (001) surface had a light transmittance of only 62%, which could not meet the application requirements of high-end power devices.

[0090] Comparative Example 2 In Comparative Example 2, the main sintering temperature in the stepwise sintering step was reduced to 1400°C, the holding time was unchanged, and the other processes and systems were the same as those of Example 2. After the stepwise sintering of Comparative Example 2 was completed, the sintered body had a density of only 78%, XRD detection showed GaOOH impurities (mainly due to insufficient sintering), and the residual pores had a size of ≥10 μm. During the crystal growth process, the bubble content in the gallium oxide melt increased sharply, and the bubble removal rate was only 42%. The final obtained gallium oxide crystal contained a large number of inclusions (bubble diameter of 5-20 μm), and the light transmittance was only 400-800 nm, which was reduced to 55%, and could not meet the application requirements of device-level.

[0091] Comparative Example 3 In Comparative Example 3, the dynamic rotation mechanism of the crucible was omitted in the melt crystal growth step, and the “crucible acceleration-deceleration-reverse rotation” step was cancelled, and the whole process was static, and the other processes and systems were the same as those of Example 3. The temperature field uniformity of the gallium oxide melt in the crucible of Comparative Example 3 was poor, and the axial gradient fluctuation increased sharply to ±15°C / cm, and a local vortex dead zone was formed in the melt, and the bubbles could not be effectively gathered and floated. Compared with the 95% bubble removal rate of Example 3, the bubble removal rate in the melt of Comparative Example 3 was reduced to 38%, and the residual bubble density in the melt was up to 25 / cm3. The final obtained gallium oxide crystal had periodic bubble stratification along the growth direction.

[0092] Comparative Example 4 Comparative Example 4 was similar to Example 2, except that the process parameters in the raw material pretreatment and stepwise sintering steps were adjusted. In Comparative Example 4, the pressing pressure in the forming step was set to 30 MPa, and the holding time was 3 minutes. In the stepwise sintering step, the temperature of the low-temperature preliminary sintering was set to 600°C, the holding time of the high-temperature sintering was 1 hour, and the process parameters of the melt crystal growth step were consistent with those of Example 2.

[0093] The porosity of the gallium oxide bulk in Comparative Example 4 was as high as 20%, the sintered body had a density of only 75%, and was full of interconnected pores with a size of about 10-50 μm. Finally, only short and small ingots with a diameter of 20 mm and a length of 30 mm were obtained, the surface was full of pits left by bubbles, and the dislocation density was >5x10 5 cm -2 , which had no practical value.

[0094] Comparative Example 5 Comparative Example 5 was similar to Example 2, except that the process parameters in the melt growth step were adjusted. In Comparative Example 5, the holding time of the melt in the melt growth step was shortened from 3 hours to 30 minutes, and the other parameters were unchanged. The process parameters of the raw material pretreatment and the staged sintering step were consistent with those in Example 2.

[0095] In Comparative Example 5, the bubbles in the gallium oxide melt were not fully escaped, and the holding time was not enough to cause the bubbles to complete the aggregation and floating, so that the removal rate of the bubbles in the melt was reduced from 97% to 52%. The obtained crystal was full of a large number of small bubbles along the axial direction of the ingot, the bubble diameter was 1-3 μm, and the density was up to 80 / mm3. The uniformity deviation of the resistivity of the gallium oxide crystal was >15%.

[0096] In summary, the method for removing the bubbles in the β-gallium oxide melt provided in the present application forms a complete and effective technical solution through the control of the raw material pretreatment, the staged sintering, the crucible rotation regulation and other links, and the removal rate of the bubbles can be increased to more than 92% by accurately controlling the conditions and parameters of each process, and the dislocation density can be controlled to be 2.5x10 3 cm -2 In the following, the resistivity radial deviation was less than 3%, and a gallium oxide single crystal material with higher quality was obtained, which provided a strong guarantee for the preparation of high-performance power devices and the like.

[0097] In the specification provided herein, a large number of specific details are described. However, it can be understood that the embodiments of the present application can be practiced without these specific details. In some examples, well-known methods, structures and techniques are not described in detail in order not to obscure the understanding of the present specification.

[0098] In addition, those skilled in the art can understand that although some embodiments described herein include certain features included in other embodiments but not other features, the combination of the features of different embodiments means that it is within the scope of the embodiments of the present application and forms different embodiments. For example, in the following claims, any one of the claimed embodiments can be used in any combination.

Claims

1. A method for removing bubbles from a gallium oxide melt, characterized in that, The method includes the following steps: (1) Raw material pretreatment: Select β-gallium oxide powder with a purity of ≥99.999%, place it in a mold, control the pressing pressure to 100-300 MPa, and hold the pressure for more than 2 minutes to press the gallium oxide powder into shape; (2) Segmented sintering treatment: The pressed gallium oxide blank is placed in a sintering furnace and first subjected to low-temperature initial sintering at a temperature not exceeding 1000℃, and then the temperature is raised to a temperature range of 1500-1700℃ for high-temperature sintering to obtain a dense gallium oxide sintered body. (3) Melt stirring control: After the gallium oxide sintered body is placed in the crucible and melted, the crucible is rotated according to the pre-set crucible dynamic rotation mechanism. The dynamic rotation includes alternating clockwise acceleration and counterclockwise deceleration, with a speed range of 5-30 rpm and a cycle number of more than 2 times.

2. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, In step (1), the particle size of the β-gallium oxide is less than 5 μm, and the pressurization method is selected from any of the following: unidirectional pressurization, bidirectional pressurization, cool isostatic pressing, hot isostatic pressing, one-time pressure forming or gradient pressure forming, and the pressurization rate is 5-10 MPa / s.

3. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, In step (2), the low-temperature initial firing is carried out in an air environment with a heating rate of 5-10℃ / min and a holding time of 2-10 h; the high-temperature sintering is carried out in an air environment with a heating rate of 1-5℃ / min and a holding time of 2-10 h.

4. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, In step (3), in a single cycle mechanism, first rotate clockwise at a predetermined acceleration to 10-30 r / min, maintain the first rotation time, then switch to counterclockwise rotation at a predetermined deceleration to 5-15 r / min, maintain the second rotation time, and the sum of the first rotation time and the second rotation time is not less than 30 minutes.

5. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, In step (3), the dynamic rotation also includes accelerating clockwise, stopping, and then decelerating counterclockwise, with a single cycle of 30-90 minutes.

6. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, It also includes step (4), in which the crystal rotation speed is V1, the crystal growth rate is V2, the axial temperature gradient of the melt is G, and the product of the rotation speed V1 and the axial temperature gradient of the melt, V1×G, is controlled to be no greater than 350. The surface of the melt is basically horizontal or concave towards the center of the melt. The product of the crystal growth rate V2 and the axial temperature gradient of the melt, V2×G, is controlled to be no greater than 35. The value range of V1 is 1-15 rpm, the value range of V2 is 0.5-5 mm / h, and the value range of G is 5-70℃ / cm.

7. A crystal growth apparatus for removing bubbles from gallium oxide melt, characterized in that, The crystal growth equipment is equipped with: The crucible speed control rotation system is used to perform programmable rotation drive on the crucible, and is adapted to a combined rotation mode of clockwise acceleration and counterclockwise deceleration. A temperature measuring device, comprising an infrared thermometer and / or a thermocouple, for synchronous temperature monitoring; as well as The control linkage system links the temperature measuring device with the heating system and crucible speed control rotation system of the crystal growth equipment. When the temperature measuring device detects an abnormal temperature gradient, the system automatically triggers an adjustment command to adjust the heating power and / or change the crucible rotation speed.

8. The crystal growth apparatus for removing bubbles from gallium oxide melt according to claim 7, characterized in that, It is also equipped with an annular gradient temperature control heat shield, which surrounds the outside of the crucible to make the axial temperature gradient of the crucible uniform and stable.

9. The β-gallium oxide single crystal obtained by any method of claims 1 to 6 or any apparatus of claims 7 to 8, characterized in that, The β-gallium oxide single crystal has a bubble removal rate of ≥90% and a resistivity radial deviation of ≤3%.

10. A power device based on β-gallium oxide single crystal, characterized in that, The power device uses β-gallium oxide single crystal as described in claim 9 as the core material, including field-effect transistors, diodes, or deep ultraviolet light detectors.

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