Preparation process of silicon carbide powder for growing silicon carbide crystals

Abstract

The invention discloses a preparation process of silicon carbide powder for growing silicon carbide crystals, which comprises the following steps: putting beta-silicon carbide powder into a graphite crucible, and putting the graphite crucible into a vacuum high-temperature furnace; then, the vacuum high-temperature furnace is vacuumized to be smaller than 1.2 torr; argon is introduced into the cavity of the vacuum high-temperature furnace, and the pressure is increased to 600 + / -30 torr; the cavity of the vacuum high-temperature furnace is heated, and heating is carried out in four stages; and cooling is started. The preparation method has the beneficial effects that silicon carbide mainly comprises an alpha phase and a beta phase in crystalline phases, beta-silicon carbide is a low-temperature stable phase, and when the silicon carbide powder prepared by the preparation method is applied to crystal growth, crystals have relatively low micro-pipeline density, plane holes and other defects; meanwhile, when the nitrogen-doped n-type silicon carbide single crystal is prepared, the doping concentration of the crystal is improved. The silicon carbide powder subjected to heat treatment is suitable for growth of silicon carbide single crystals and epitaxial wafers in various crystalline states.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials, and more particularly to a process for preparing silicon carbide powder for growing silicon carbide crystals. Background Technology

[0002] Silicon carbide (SiC) crystals possess excellent chemical, physical, and mechanical properties, and are widely recognized as broadband semiconductor materials suitable for high-temperature, high-frequency, and high-power devices. They are also used as substrate materials for optoelectronic and electronic communication devices (such as blue / white light-emitting diodes and gallium nitride (SiC) microwave devices grown on SiC). For these device applications, the growth technology of large-size SiC crystals with low defect density has been well-developed. However, despite numerous research and development efforts being completed and published, the occurrence of defects caused by crystal growth, such as micropipes, planar defects, dislocations, and polymorphic inclusions, remains under discussion, and the entire mechanism of their occurrence is not yet fully understood. In particular, published studies have confirmed that the polymorphisms formed during crystal growth are significantly influenced by the chemical species within the SiC growth source.

[0003] Silicon carbide has at least 70 crystalline forms. α-Silicon carbide is the most common allotropic form, formed at temperatures above 2000°C, and has a hexagonal crystal structure (similar to wurtzite). β-Silicon carbide, with a cubic crystal structure similar to diamond, is formed at temperatures below 2000°C. Although it is noteworthy for its higher surface area per unit area compared to the α-type in heterogeneous catalyst support applications, it has not yet found commercial application. On the other hand, while α-silicon carbide is known to have suitable stoichiometric composition, there are currently no commercial suppliers of high-purity α-silicon carbide. Furthermore, simulation results report that the porosity and particle size of the growth source are related to the thermal field distribution in the graphite furnace, but the influence of individual powder porosity on growth characteristics has not been reported. Therefore, it is necessary to develop a process for preparing silicon carbide powder for growing silicon carbide crystals. A search revealed no technical solution identical to this invention. Summary of the Invention

[0004] The main technical problem solved by this invention is to provide a process for preparing silicon carbide powder for growing silicon carbide crystals, thereby solving one or more of the problems in the prior art.

[0005] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: a process for preparing silicon carbide powder for growing silicon carbide crystals, the innovation of which is: including the following steps:

[0006] 1) Place β-silicon carbide powder into a graphite crucible, and then place the graphite crucible into a vacuum high-temperature furnace; then, evacuate the vacuum high-temperature furnace to less than 1.2 torr;

[0007] 2) Then, argon gas is introduced into the vacuum high-temperature furnace cavity to increase the pressure to 600±30 torr;

[0008] 3) The cavity of the vacuum high-temperature furnace is then heated in four stages, with different heating / cooling rates for each stage: In the first stage, the temperature is increased to 2200℃ at (400℃±20℃) / hour; in the second stage, the temperature is decreased to 700℃ at (100℃±20℃) / hour; in the third stage, the cavity temperature is increased to 1800℃ at (200℃±20℃) / hour; and in the fourth stage, the cavity temperature is increased to 2100℃ at (150℃±20℃) / hour, and maintained at this temperature for 5 hours, with a temperature error not exceeding ±20℃.

[0009] 4) Start cooling down. Within 12 hours, reduce the cavity temperature of the vacuum high-temperature furnace to room temperature to obtain the powder source material suitable for silicon carbide crystal growth.

[0010] In some embodiments, in step 1), the β-silicon carbide powder has a purity of 99.99% or higher and is composed of 1μm-2μm particles aggregated into porous spheres with a size of 400μm-450μm.

[0011] In some implementations, in step 2), the flow rate of argon gas is 45-50 sccm.

[0012] The beneficial effects of this invention are as follows: Silicon carbide mainly exists in two phases: α-phase and β-phase. β-silicon carbide is a low-temperature stable phase, and theoretically, it transforms into α-silicon carbide above 2100℃. Typically, what we see in the market is α-silicon carbide, but its purity is low. Although some β-silicon carbide exists on the outer layer during the preparation of α-silicon carbide in this technical solution, it is basically discarded during furnace dismantling. This invention targets commercially available high-purity β-silicon carbide powder and, through further heat treatment, effectively transforms it into α-silicon carbide powder. α-silicon carbide has a suitable stoichiometric composition, making it suitable as a crystal growth raw material, minimizing the influence of porous powder and maximizing the effect of crystal powder in crystal growth. The optimized heat treatment temperature curve of this invention is crucial; insufficient time or too low a temperature cannot completely eliminate free metallic silicon and porous powder in the original powder; conversely, too long or too high a time will cause graphitization of the powder.

[0013] The silicon carbide powder prepared by this invention is used in crystal growth, and the crystals exhibit relatively low microchannel density and planar voids. Simultaneously, it is used in the preparation of nitrogen-doped n-type silicon carbide single crystals, increasing the doping concentration. The heat-treated silicon carbide powder of this invention is suitable for the growth of silicon carbide single crystals and epitaxial wafers of various crystal states. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] The embodiments of the present invention include:

[0016] A process for preparing silicon carbide powder for growing silicon carbide crystals includes the following steps:

[0017] 1) Place β-silicon carbide powder into a graphite crucible, and then place the graphite crucible into a vacuum high-temperature furnace; then, evacuate the vacuum high-temperature furnace to less than 1.2 torr;

[0018] 2) Then, argon gas is introduced into the vacuum high-temperature furnace cavity to increase the pressure to 600±30 torr;

[0019] 3) The cavity of the vacuum high-temperature furnace is then heated in four stages, with different heating / cooling rates for each stage: In the first stage, the temperature is increased to 2200℃ at (400℃±20℃) / hour; in the second stage, the temperature is decreased to 700℃ at (100℃±20℃) / hour; in the third stage, the cavity temperature is increased to 1800℃ at (200℃±20℃) / hour; and in the fourth stage, the cavity temperature is increased to 2100℃ at (150℃±20℃) / hour, and maintained at this temperature for 5 hours, with a temperature error not exceeding ±20℃.

[0020] 4) Start cooling down. Within 12 hours, reduce the cavity temperature of the vacuum high-temperature furnace to room temperature to obtain the powder source material suitable for silicon carbide crystal growth.

[0021] In some embodiments, in step 1), the β-silicon carbide powder has a purity of 99.99% or higher and is composed of 1μm-2μm particles aggregated into porous spheres with a size of 400μm-450μm.

[0022] In some implementations, in step 2), the flow rate of argon gas is 45-50 sccm.

[0023] Silicon carbide exists primarily in two crystalline phases: α-phase and β-phase. β-silicon carbide is a low-temperature stable phase, theoretically transforming into α-silicon carbide above 2100℃. What we typically see in the market is α-silicon carbide, but its purity is low. Although some β-silicon carbide exists on the outer layer during the preparation of α-silicon carbide in this technical solution, it is generally discarded during furnace dismantling. This invention utilizes further heat treatment of commercially available high-purity β-silicon carbide powder to effectively transform it into α-silicon carbide powder. α-silicon carbide has a suitable stoichiometric composition, making it suitable as a crystal growth raw material, minimizing the influence of porous powder and maximizing the crystal growth effect. The optimized heat treatment temperature curve of this invention is crucial; insufficient time or too low a temperature cannot completely eliminate free metallic silicon and porous powder in the original powder; conversely, too long or too high a time will cause powder graphitization.

[0024] The silicon carbide powder prepared by this invention is used in crystal growth, and the crystals exhibit relatively low microchannel density and planar voids. Simultaneously, it is used in the preparation of nitrogen-doped n-type silicon carbide single crystals, increasing the doping concentration. The heat-treated silicon carbide powder of this invention is suitable for the growth of silicon carbide single crystals and epitaxial wafers of various crystal states.

[0025] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A process for preparing silicon carbide powder for growing silicon carbide crystals, characterized in that: Includes the following steps: 1) Place β-silicon carbide powder into a graphite crucible, and then place the graphite crucible into a vacuum high-temperature furnace; then, evacuate the vacuum high-temperature furnace to less than 1.2 torr; 2) Then, argon gas is introduced into the vacuum high-temperature furnace cavity to increase the pressure to 600±30 torr; 3) The cavity of the vacuum high-temperature furnace is then heated in four stages, with different heating / cooling rates for each stage: In the first stage, the temperature is increased to 2200℃ at (400℃±20℃) / hour; in the second stage, the temperature is decreased to 700℃ at (100℃±20℃) / hour; in the third stage, the cavity temperature is increased to 1800℃ at (200℃±20℃) / hour; and in the fourth stage, the cavity temperature is increased to 2100℃ at (150℃±20℃) / hour, and maintained at this temperature for 5 hours, with a temperature error not exceeding ±20℃. 4) Start cooling down. Within 12 hours, reduce the cavity temperature of the vacuum high-temperature furnace to room temperature to obtain the powder source material suitable for silicon carbide crystal growth.

2. The preparation process of silicon carbide powder for growing silicon carbide crystals according to claim 1, characterized in that: In step 1), the β-silicon carbide powder has a purity of 99.99% or higher, and is composed of 1μm-2μm particles aggregated into porous spheres with a size of 400μm-450μm.

3. The preparation process of silicon carbide powder for growing silicon carbide crystals according to claim 1, characterized in that: In step 2), the flow rate of argon gas is 45-50 sccm.