Preparation method of airtight sintering material for high-temperature sublimation device
By adding tungsten and tungsten carbide to the tantalum carbide powder, and performing cold isostatic pressing preparation and multi-stage sintering treatment, the problem of mismatch between densification and thermal expansion of crucible materials at high temperatures is solved, and efficient and stable AlN crystal growth is achieved.
Patent Information
- Application Number
- CN202411986421.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2025-05-13
AI Technical Summary
The prior art is difficult to achieve densification of crucible materials such as tantalum carbide and tungsten carbide at high temperatures, resulting in the problems of thermal expansion mismatch and abnormal grain growth during the AlN crystal growth process.
By adding tungsten powder and tungsten carbide powder to tantalum carbide powder, performing cold isostatic pressing preparation and multi-stage sintering treatment, the thermal expansion coefficient and grain growth of the material are controlled, thereby preparing an airtight sintered material with excellent airtightness and mechanical properties.
The thermal stability and chemical stability of the material are achieved at high temperatures, the stress and cracks during AlN growth are reduced, the airtightness of the crucible and the adhesion of AlN crystals are improved, and the efficient and stable growth of AlN crystals is ensured.
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of semiconductor material preparation, and in particular to a method for preparing a gas-tight sintered material for a high-temperature sublimation device. Background Art
[0002] As an ultra-wide bandgap semiconductor material, aluminum nitride has the advantages of high bandgap width (6.2eV), high thermal conductivity (340W (m·K)), high breakdown field strength, good ultraviolet transmittance, chemical and thermal stability, etc. It is an ideal material for ultraviolet optoelectronic devices and can be widely used in deep ultraviolet LEDs, ultraviolet curing, ultraviolet detectors and other fields. It has broad application prospects and is the current research focus in the field of semiconductor materials.
[0003] In the process of AlN crystal growth, physical vapor transport (PVT) technology is the most commonly used growth technology, which requires the crucible material to maintain thermal and chemical stability at high temperatures of 1850-2200°C, while maintaining performance during multiple growth cycles to meet economic requirements. Therefore, finding a suitable crucible material has become the key to technological development. Tantalum carbide (TaC) and tungsten carbide (WC) are two particularly promising materials that can improve the sintering process, reduce grain growth, and adjust the thermal expansion coefficient to match AlN by adding a small amount of additives (such as tungsten, tantalum, and niobium). However, traditional sintering methods for preparing these crucible materials make it difficult to achieve their densification because these materials have a high degree of covalent bonding characteristics and a low self-diffusion coefficient.
[0004] Therefore, there is an urgent need to develop a new type of airtight sintered crucible material for high-temperature AlN crystal growth, and to control the thermal expansion coefficient and grain growth of the crucible material to achieve a more efficient and stable AlN crystal growth process to meet the current demand for high-performance semiconductor material AlN. Summary of the invention
[0005] Based on the above existing technical problems, the present invention intends to provide a new type of airtight sintered material that can meet the use requirements of high-temperature sublimation devices such as crucibles for growing AlN crystals by physical vapor transport method, and maintain thermal stability and chemical stability at high temperatures.
[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions.
[0007] The invention provides a method for preparing a gas-tight sintered material for a high-temperature sublimation device, comprising the following steps.
[0008] Step 1: Add either or both of tungsten powder and tungsten carbide powder to tantalum carbide (TaC) powder and mix them evenly to form a mixed powder.
[0009] Step 2: Place the mixed powder in a mold and perform cold isostatic pressing at a certain pressure P to prepare a compact, and maintain the pressure for a period of time t1.
[0010] Step 3: The pressed body is subjected to pressureless pre-sintering in a high-temperature graphite furnace, and the temperature is raised from room temperature to a relatively low temperature T1 at a high heating rate V1, and then the temperature is further raised to a relatively high temperature T2 at a low heating rate V2, and the temperature is kept for a period of time t2; the cooling process is carried out in the opposite procedure of the heating process, first the temperature is lowered from T2 to T1 at a cooling rate of V2, and then the cooling rate is increased to V1 to room temperature to obtain a pre-sintered body.
[0011] Step 4: Cut and grind the pre-sintered body into a disc shape, sinter under vacuum conditions, increase the temperature to T3 at a high heating rate of V3, and then increase the temperature from T3 to T4 at a low heating rate of V4, and keep the temperature for a period of t3; the cooling process is carried out in the opposite procedure of the heating process in this step, first reduce the temperature from T4 to T3 at a cooling rate of V4, and then increase the cooling rate to V3 to room temperature to complete the sintering.
[0012] Step 5: Machining the sintered disk into a component for the high temperature sublimation device, such as a TaC crucible used in the high temperature sublimation device (such as a PVT growth furnace for AlN single crystal growth).
[0013] Specifically, in step 1, the added amount of tungsten powder or tungsten carbide powder is 1-5wt% of the mixed powder.
[0014] Preferably, the particle size of the tantalum carbide powder in step 1 is 50-200 μm.
[0015] Preferably, in step 1, the particle size of the tungsten powder is 0.1-10 μm; the particle size of the tungsten carbide is 0.1-20 μm.
[0016] Preferably, in step 2, the pressure P is 0.1-5 GPa; and the t1 is 1-10 min.
[0017] Preferably, in step 3, the heating rate V1 is 2-5°C / min, the heating rate V2 is 0.1-2°C / min, the temperature T1 is 1100°C-1200°C, the temperature T2 is 1700°C-1800°C, and the insulation time t2 is 1-10h.
[0018] Preferably, in step 4, the heating rate V3 is 1-10°C / min, the heating rate V4 is 0.1-2°C / min, the temperature T3 is 1700°C-1900°C, the temperature T4 is 2000°C-2200°C, and the insulation time t3 is 5-20h.
[0019] Preferably, the particle size of the TaC crucible prepared in step 5 is 10-50 μm.
[0020] Compared with the prior art, the present invention has the following advantages:
[0021] The airtight TaC crucible prepared by the present invention has excellent airtightness at high temperatures, which is very important for preventing gas leakage and maintaining a specific atmosphere during the growth of AlN crystals.
[0022] The present invention effectively reduces the growth of TaC grains by adding 1-5wt% of tungsten (W) powder or tungsten carbide (WC) powder to tantalum carbide (TaC). Additives such as tungsten or tungsten carbide can affect the growth behavior of grains during sintering. The addition of tungsten and tungsten carbide will form obstacles at the grain boundaries, thereby inhibiting the abnormal growth of grains. The formation of Ta2C or W2C at the TaC grain boundaries can pin the grain boundaries and inhibit grain growth. This pinning effect reduces the growth of grains, resulting in a reduction in grain size so that it is controlled within the range of 10-50μm. In addition to improving the airtightness of the crucible made of the material, the mechanical properties and thermal stability of the material are also improved.
[0023] The present invention adjusts the thermal expansion coefficient of TaC by adding W and WC, making it closer to the thermal expansion coefficient of AlN, thereby reducing stress and cracks caused by thermal expansion mismatch during the growth of AlN.
[0024] Ceramic discs with a higher tungsten content prepared using the present invention show better AlN adhesion, which is very important for the bonding of the crystal to the crucible cover during the growth process and subsequent processing.
[0025] When the crucible cover prepared by the present invention is used to grow AlN crystal, the interface of the prepared AlN crystal and the crucible cover is completely closed without gaps, which helps to improve the quality of the crystal. DETAILED DESCRIPTION
[0026] The preparation method of the airtight sintered material of the present invention is further explained and illustrated in conjunction with specific embodiments below.
[0027] Embodiment 1
[0028] Step 1: Add 2 wt% of high-purity tungsten powder of the mixed powder to TaC powder with a particle size of 100-150 μm to form a mixed powder, wherein the particle size of the tungsten powder is 0.5-1 μm.
[0029] Step 2: Place the mixed powder in a mold and perform cold isostatic pressing to prepare a pressed body. Apply a uniform pressure of 0.1 GPa and maintain the pressure for 10 minutes.
[0030] Step 3: Pre-sinter the compacted body without pressure in a high-temperature graphite furnace: Place the compacted powder in a high-temperature furnace, and heat the powder from room temperature to a relatively low temperature of 1100°C at a heating rate of 5°C / min. Continue to heat the powder, and heat it to a relatively high temperature of 1750°C at a low heating rate of 1°C / min, and keep it warm for 5 hours. The cooling process is carried out in the opposite order of the heating process, first cooling from a relatively high temperature of 1750°C to 1100°C at 1°C / min, and then increasing the cooling rate, cooling from 1100°C to room temperature at 5°C / min to obtain a pre-sintered body.
[0031] Step 4: Cut and grind the pre-sintered body into a disc shape. Under vacuum conditions, the disc-shaped pre-sintered body is first heated to 1800°C at a high heating rate of 4°C / min, and then heated to 2100°C at a low heating rate of 1°C / min from 1800°C, and kept at this temperature for 8 hours. The cooling process is carried out in the opposite order of the heating process, firstly decreasing from a relatively high temperature of 2100°C to 1800°C at 1°C / min, and then increasing the cooling rate to decrease from 1800°C to room temperature at 4°C / min.
[0032] Step 5: The sintered disc is machined into a special-shaped crucible, and the grain size of the sintered TaC crucible is measured to be 10-15 μm.
[0033] Embodiment 2
[0034] Step 1: Add 1wt% of high-purity tungsten powder and 4wt% of high-purity tungsten carbide powder of the mixed powder to TaC powder with a particle size of 50-100μm to form a mixed powder, wherein the particle size of the tungsten powder is 0.2-0.8μm, and the particle size of the tungsten carbide powder is 4-5μm.
[0035] Step 2: Place the mixed powder in a mold and perform cold isostatic pressing to prepare a compact, uniformly apply a pressure of 0.8 GPa, and maintain the pressure for 4 minutes.
[0036] Step 3: The compacted body is subjected to pressureless pre-sintering in a high-temperature graphite furnace: The compacted powder is placed in a high-temperature furnace, and the powder is first heated from room temperature to a relatively low temperature of 1150°C at a heating rate of 5°C / min, and the powder is continued to be heated, and the temperature is raised to a relatively high temperature of 1800°C at a low heating rate of 0.5°C / min, and kept at this temperature for 10 hours. The cooling process is carried out in the opposite procedure of the heating process, firstly from a relatively high temperature of 1800°C to 1150°C at a rate of 0.5°C / min, and then the cooling rate is increased, and the temperature is lowered from 1150°C to room temperature at a rate of 5°C / min to obtain a pre-sintered body.
[0037] Step 4: Cut and grind the pre-sintered body into a disc shape. Under low vacuum conditions, the disc-shaped pre-sintered body is first heated to 1900°C at a high heating rate of 6°C / min, then heated to 2200°C at a low heating rate of 2°C / min, and kept at this temperature for 5 hours. The cooling process is carried out in the opposite order of the heating process, firstly decreasing from a relatively high temperature of 2200°C to 1900°C at 2°C / min, and then increasing the cooling rate to decrease from 1900°C to room temperature at 6°C / min.
[0038] Step 5: The sintered disc is machined into a special-shaped crucible, and the grain size of the sintered TaC crucible is measured to be 25-30 μm.
[0039] Embodiment 3
[0040] Step 1: Add 5wt% of high-purity tungsten carbide powder to TaC powder with a particle size of 150-200μm to form a mixed powder, wherein the particle size of the tungsten carbide powder is 0.1-0.5μm.
[0041] Step 2: Place the mixed powder in a mold and prepare a pressed body by cold isostatic pressing. Apply a uniform pressure of 5 GPa and maintain the pressure for 1 minute.
[0042] Step 3: Pre-sinter the compacted body without pressure in a high-temperature graphite furnace: Place the compacted powder in a high-temperature furnace, and heat the powder from room temperature to a relatively low temperature of 1200°C at a heating rate of 2°C / min. Continue to heat the powder, and heat it to a relatively high temperature of 1700°C at a low heating rate of 0.1°C / min, and keep it warm for 8 hours. The cooling process is carried out in the opposite order of the heating process, first cooling from a relatively high temperature of 1700°C to 1200°C at 0.1°C / min, and then increasing the cooling rate, cooling from 1200°C to room temperature at 2°C / min to obtain a pre-sintered body.
[0043] Step 4: The pre-sintered sample was cut and ground into a disc shape. Under vacuum conditions, the circular pre-sintered body was first heated to 1700°C at a high heating rate of 1°C / min, and then heated to 2000°C at a low heating rate of 0.1°C / min, and kept at this temperature for 20 hours. The cooling process was carried out in the opposite order of the heating process, firstly decreasing from a relatively high temperature of 2000°C to 1700°C at a rate of 0.1°C / min, and then increasing the cooling rate to decrease from 1700°C to room temperature at a rate of 1°C / min.
[0044] Step 5: The sintered disc is machined into a special-shaped crucible, and the grain size of the sintered TaC crucible is measured to be 30-50 μm.
[0045] Embodiment 4
[0046] Step 1: Add 5wt% of high-purity tungsten powder and 1wt% of high-purity tungsten carbide powder of the mixed powder to TaC powder with a particle size of 50-100μm to form a mixed powder, wherein the particle size of the tungsten powder is 0.1-0.8μm, and the particle size of the tungsten carbide powder is 4-5μm.
[0047] Step 2: Place the mixed powder in a mold and perform cold isostatic pressing to prepare a pressed body. Apply a uniform pressure of 0.8 GPa and maintain the pressure for 8 minutes.
[0048] Step 3: The compacted body is subjected to pressureless pre-sintering in a high-temperature graphite furnace: The compacted powder is placed in a high-temperature furnace, and the powder is first heated from room temperature to a relatively low temperature of 1150°C at a heating rate of 5°C / min, and the powder is continued to be heated, and the temperature is raised to a relatively high temperature of 1800°C at a low heating rate of 2°C / min, and kept at this temperature for 1 hour. The cooling process is carried out in the opposite procedure of the heating process, firstly from a relatively high temperature of 1800°C to 1150°C at a rate of 2°C / min, and then the cooling rate is increased, and the temperature is lowered from 1150°C to room temperature at a rate of 5°C / min to obtain a pre-sintered body.
[0049] Step 4: Cut and grind the pre-sintered body into a disc shape. Under low vacuum conditions, the disc-shaped pre-sintered body is first heated to 1900°C at a high heating rate of 10°C / min, then heated to 2200°C at a low heating rate of 2°C / min, and kept at this temperature for 5 hours. The cooling process is carried out in the opposite order of the heating process, firstly decreasing from a relatively high temperature of 2200°C to 1900°C at 2°C / min, and then increasing the cooling rate to decrease from 1900°C to room temperature at 10°C / min.
[0050] Step 5: The sintered disc is machined into a special-shaped crucible, and the grain size of the sintered TaC crucible is measured to be 20-30 μm.
[0051] The above embodiments are only used to help understand the method and core idea of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing a gastight sintered material for a high temperature sublimation device, characterized in that: The steps include: Step 1, adding either or both of tungsten powder and tungsten carbide powder to tantalum carbide powder, and mixing them evenly to form a mixed powder; Step 2, placing the mixed powder in a mold, performing cold isostatic pressing under a pressure P to obtain a pressed body, and maintaining the pressure for a period of time t1; Step 3, the pressed body is subjected to pressureless pre-sintering in a high-temperature graphite furnace, the temperature is raised from room temperature to temperature T1 at a heating rate V1, and then the temperature is further raised to temperature T2 at a heating rate V2, and the temperature is kept for a period of time t2; the cooling process is carried out in the opposite order of the heating process in this step, firstly the temperature is lowered from T2 to T1 at a cooling rate V2, and then the temperature is lowered to room temperature at a cooling rate V1 to obtain a pre-sintered body; wherein V1>V2; Step 4, cutting and grinding the pre-sintered body into a disc shape, sintering under vacuum conditions, first heating the temperature to T3 at a heating rate of V3, then heating the temperature from T3 to T4 at a heating rate of V4, and keeping the temperature for a period of t3; the cooling process is carried out in the opposite order of the heating process in this step, first cooling the temperature from T4 to T3 at a cooling rate of V4, and then cooling the temperature to room temperature at a cooling rate of V3 to complete the sintering; wherein V3>V4; Step 5: machining the sintered disc into a component for use in the high-temperature sublimation device.
2. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 1, characterized in that: In step 1, the addition amount of tungsten powder or tungsten carbide powder is 1-5wt% of the mixed powder.
3. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 2, characterized in that: The particle size of tungsten powder is 0.1-10μm; the particle size of tungsten carbide is 0.1-20μm.
4. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 1, characterized in that: The particle size of the tantalum carbide powder in step 1 is 50-200 μm.
5. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 1, characterized in that: The pressure P in step 2 is 0.1-5 GPa; The t1 is 1-10 min.
6. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 1, characterized in that: In step 3, the heating rate V1 is 2-5°C / min, the heating rate V2 is 0.1-2°C / min, the temperature T1 is 1100°C-1200°C, the temperature T2 is 1700°C-1800°C, and the insulation time t2 is 1-10h.
7. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 1, characterized in that: In step 4, the heating rate V3 is 1-10°C / min, the heating rate V4 is 0.1-2°C / min, the temperature T3 is 1700°C-1900°C, the temperature T4 is 2000°C-2200°C, and the insulation time t3 is 5-20h.
8. The method for preparing a gas-tight sintered material for a high-temperature sublimation device according to claim 1, wherein the high-temperature sublimation device is a PVT high-temperature furnace for growing AlN single crystals.
9. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 1, wherein the component for the high temperature sublimation device in step 5 is a TaC crucible.
10. The method for preparing a gastight sintered material for a high temperature sublimation device according to claim 9, characterized in that: The particle size of the TaC crucible prepared in step 5 is 10-50 μm.