A method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth

Abstract

This invention discloses a method for loading and nitrogen removal during the PVT (Polymer Transformation) process for growing semi-insulating silicon carbide crystals. The method includes: first, loading silicon carbide powder into a crucible within an argon-filled glove box; transferring the crucible to a PVT growth furnace for pre-firing of the silicon carbide powder at 1000°C; cooling to 100°C, removing the crucible, and placing it in an argon-filled glove box; loading the crucible with a seed crystal lid into the glove box to seal it, then returning it to the PVT growth furnace; performing a vacuum leak test, and after passing the test, starting heating; vacuum heating to 1000°C, then cooling to 300°C, repeating this process 2-3 times, before proceeding with the formal heating and growth process, during which an argon-hydrogen mixture or argon gas is circulated. The advantages of this invention are: it effectively reduces nitrogen entering the crucible during loading; and it optimizes the nitrogen removal, heating, and loading methods, effectively reducing nitrogen residue, improving silicon carbide crystal quality, thereby increasing resistivity, and ultimately improving the quality of intrinsic semi-insulating silicon carbide substrates.

Description

Technical Field

[0001] This invention relates to a method for charging and nitrogen removal in the process of growing semi-insulating silicon carbide PVT crystals, belonging to the technical field of semi-insulating silicon carbide PVT crystal growth. Background Technology

[0002] With the rapid development of information technology, semiconductor technology innovation is playing an increasingly important role. Wide-bandgap semiconductor materials, represented by silicon carbide (SiC) and gallium nitride (GaN), are the third generation of semiconductors after silicon (Si) and gallium arsenide (GaAs). Among them, intrinsically semi-insulating silicon carbide has advantages such as high resistivity, high breakdown field strength, high thermal conductivity, high saturation drift electron velocity, and high bonding energy, making it one of the most promising materials in the semiconductor field.

[0003] The graphite components, furnace loading, and thermal adsorption processes involve contact with large amounts of nitrogen, which is the biggest obstacle to the growth of intrinsic semi-insulating silicon carbide substrates. In existing PVT silicon carbide crystal growth equipment, high-purity argon or a high-purity argon-hydrogen mixture is generally used to purge nitrogen, but this is ineffective and often results in incomplete nitrogen removal, affecting the quality of the silicon carbide crystals and causing resistivity values ​​to fail to meet requirements, thus impacting the quality of the intrinsic semi-insulating silicon carbide substrate. Summary of the Invention

[0004] This invention proposes a method for loading and nitrogen removal in the process of growing semi-insulating silicon carbide crystals using the PVT method. The purpose is to overcome the above-mentioned shortcomings of the existing technology, reduce the amount of nitrogen entering the crucible during the loading process, improve the quality of silicon carbide crystals, increase the resistivity value, and improve the quality of intrinsic semi-insulating silicon carbide substrates.

[0005] The technical solution of this invention: a method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth, comprising the following steps: 1. First, load the silicon carbide powder into the crucible inside the argon glove box; 2. Transfer the crucible to the PVT growth furnace for pre-calcination of silicon carbide powder at a temperature of 1000℃; 3. Cool to 100℃, remove the crucible containing the powder and transfer it to an argon glove box to stand. 4. Load the material into the glove box with the seed crystal lid to seal the crucible, and then reload it into the PVT growth furnace. 5. Perform vacuum leak testing on the PVT growth furnace. If it passes the test, start heating. Heat the furnace to 1000℃ under vacuum and then cool it to 300℃. Repeat this process 2-3 times before proceeding with the formal heating and growth. During this process, argon-hydrogen mixture or argon gas is introduced.

[0006] Preferably, in step 1, a porous graphite sheet is used as the cover, instead of a graphite cover.

[0007] Preferably, the silicon carbide powder pre-calcination treatment in step 2 is vacuum heating, and the furnace is first evacuated before heating, with a leakage rate of <0.00085 Pa / min.

[0008] Preferably, in step 2, the pre-burning treatment time is 5 hours, the temperature is heated to 1000°C, and stabilized at 1000°C for 2 hours. Then, the power is turned off and the temperature is cooled while argon gas is introduced to assist in the gas exchange and cooling.

[0009] Preferably, in step 3, the mixture is left to cool in an argon glove box for 1 hour.

[0010] Preferably, in step 4, after removing the porous graphite sheet, the crucible with the seed crystal lid is loaded.

[0011] Preferably, in step 5, the vacuum leak detection has a leak rate of <0.0007 Pa / min.

[0012] Preferably, in step 5, the vacuum heating is carried out for 5 hours to 1000°C, and then maintained at 1000°C for 1 hour before the power is stopped and the temperature is cooled to 300°C.

[0013] The advantages of this invention are: the method is reasonably designed, which can effectively reduce the amount of nitrogen entering the crucible during the loading process; and the process of nitrogen removal, heating and loading is optimized, which can effectively reduce nitrogen residue, effectively improve the quality of silicon carbide crystal, thereby increasing the resistivity value, and ultimately effectively improving the quality of intrinsic semi-insulating silicon carbide substrate. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to embodiments and specific implementation methods.

[0015] A method for charging and nitrogen removal during semi-insulating silicon carbide PVT crystal growth includes the following steps: 1. First, put the silicon carbide powder into the crucible in a high-purity argon glove box (purity above 99.999%, water and oxygen content <3ppm); 2. Transfer the crucible to the PVT growth furnace for pre-calcination of silicon carbide powder at a temperature of approximately 1000℃. 3. Cool to 100℃, remove the crucible containing the powder and transfer it to a high-purity argon glove box to stand for a period of time; 4. Load the material into the glove box with the seed crystal lid to seal the crucible, and then reload it into the PVT growth furnace. 5. Perform vacuuming and leak testing on the PVT growth furnace. Once it passes the test, begin heating. Heat under vacuum to approximately 1000°C, then cool to 300°C. Repeat this process 2-3 times before proceeding with the formal heating and growth process. During this period, purge the furnace with a mixture of high-purity argon and hydrogen or high-purity argon.

[0016] Example: 8-inch induction crystal growth furnace, top cover discharge method Step 1: In the high-purity (purity ≥99.999%) argon glove box operating room, put the semi-insulating silicon carbide powder into the graphite crucible. This time, do not use a graphite cover, but use a porous graphite sheet to cover the surface. Step 2: Transfer the crucible filled with powder to an 8-inch induction furnace, close the furnace and evacuate it. After leak testing (leakage rate < 0.00085 Pa / min) passes, start vacuum heating. Heat the crucible to about 1000°C for about 5 hours, stabilize the temperature at 1000°C for 2 hours, then turn off the power to cool it down and pass high-purity argon gas to assist in gas exchange and cooling. Step 3: After cooling to 100°C, remove the crucible and transfer it to the high-purity argon glove box operating room, and let it stand and cool for 1 hour. Step 4: Remove the porous graphite sheet from the glove box, tighten and seal the crucible lid with seed crystal and the crucible, and then put the crucible back into the 8-inch induction crystal growth furnace. Step 5: Perform vacuum leak testing on the 8-inch induction crystal growth furnace. After passing the leak test (leakage rate < 0.0007 Pa / min), vacuum heat to about 1000℃ for 5 hours, maintain the temperature at 1000℃ for 1 hour, stop the power and cool to about 300℃, then reheat to 1000℃. Repeat this process 2-3 times. Step 6: After cooling to 300℃ for the third time, proceed with formal heating and growth. After the pressure is reduced during formal crystal growth, high-purity argon or a high-purity argon-hydrogen mixture is introduced with a purity ≥99.999%.

[0017] Experiments 1-5 are conducted below. Experiment 3 follows the same steps as the example, while the remaining experiments are comparative examples with slightly different steps. The specific differences and the experimental data on the mean resistivity of the crystals obtained are shown in the table below:

[0018] Based on the above results, it can be seen that the crystal obtained by the steps of the embodiment has the highest average resistivity and the best quality. The choice of porous graphite sheets in step 1 is due to their strong venting capacity, ease of installation and removal, and minimal impact during removal (stronger venting than graphite, easier installation and removal, and less carbon pollution). They also effectively prevent other impurities (microparticles, dust, gases, etc.) from entering the graphite crucible, reducing the crystal microtubes. Step 5 involves repeating the heating process three times. Because the gas expands after high-temperature heating, a large amount of nitrogen is evacuated. Upon cooling, the gas contracts, adsorbing only the high-purity argon gas introduced during the contraction process. Multiple cycles minimize the nitrogen content, achieving a high-argon, extremely low-nitrogen environment, ultimately reducing the resistivity of the semi-insulating crystal affected by nitrogen. Multiple cycles increase the resistivity of the semi-insulating ingot.

[0019] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for charging and nitrogen removal during the semi-insulating silicon carbide PVT crystal growth process, characterized in that, Includes the following steps:

1. First, load the silicon carbide powder into the crucible inside the argon glove box; 2. Transfer the crucible to the PVT growth furnace for pre-calcination of silicon carbide powder at a temperature of 1000℃; 3. Cool to 100℃, remove the crucible containing the powder and transfer it to an argon glove box to stand.

4. Load the material into the glove box with the seed crystal lid to seal the crucible, and then reload it into the PVT growth furnace.

5. Perform vacuum leak testing on the PVT growth furnace. If it passes the test, start heating. Heat the furnace to 1000℃ under vacuum and then cool it to 300℃. Repeat this process 2-3 times before proceeding with the formal heating and growth. During this process, argon-hydrogen mixture or argon gas is introduced.

2. The method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth as described in claim 1, characterized in that, In step 1, a porous graphite sheet is used as a cover, instead of a graphite cap.

3. The method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth as described in claim 1, characterized in that, The silicon carbide powder pre-calcination treatment in step 2 is vacuum heating. Before heating, the furnace is evacuated and the leakage rate is <0.00085 Pa / min.

4. The method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth as described in claim 1, characterized in that, In step 2, the pre-burning treatment time is 5 hours, heating to 1000℃ and stabilizing at 1000℃ for 2 hours, then power is cut off for cooling while argon gas is introduced to assist in gas exchange and cooling.

5. The method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth as described in claim 1, characterized in that, In step 3, the mixture is left to cool in an argon glove box for 1 hour.

6. The method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth as described in claim 2, characterized in that, In step 4, after removing the porous graphite sheet, the material is loaded into the crucible with the seed crystal lid.

7. The method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth as described in claim 1, characterized in that, In step 5, a vacuum leak test is performed, and the leak rate is <0.0007 Pa / min.

8. The method for charging and nitrogen removal in the process of semi-insulating silicon carbide PVT crystal growth as described in claim 1, characterized in that, In step 5, vacuum heating is performed for 5 hours to 1000°C, and the temperature is maintained at 1000°C for 1 hour before power is turned off and the temperature is cooled to 300°C.

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