Method for recycling silicon carbide secondary raw material

Abstract

The invention discloses a method for recycling a silicon carbide secondary raw material, raw materials in a low-temperature region of a raw material region can be utilized in a high-temperature region along with downward movement of a crucible, and the share of available raw materials is increased. After crystal growth, the raw material domain surface polycrystalline blocks can be processed into 8-20-mesh raw materials for secondary utilization. Through a special charging mode, the problem that the carbon-silicon ratio of a secondary raw material is unbalanced can be solved, so that the raw material can be repeatedly used.

Description

Technical Field

[0001] The invention relates to the field of silicon carbide, and in particular to a method for recycling secondary raw materials of silicon carbide. Background Art

[0002] With the development of the semiconductor industry, silicon carbide is receiving widespread attention. As a third-generation semiconductor, this material has excellent properties such as bandgap, drift velocity, breakdown voltage, thermal conductivity, high temperature resistance, etc. that are several times higher than traditional silicon carbide, and has irreplaceable advantages in electronic applications such as high temperature, high pressure and high frequency. At present, the growth of silicon carbide single crystals has entered the stage of mass production to reduce costs and increase efficiency, so how to reduce production costs is the focus of current work. The specific process of silicon carbide PVT crystal growth includes seed crystal processing, seed crystal bonding, crucible structure design, temperature field formulation, temperature control, process formulation, ingot cutting, wafer polishing, testing, and substrate.

[0003] However, in the current process of reducing costs and increasing efficiency, the most urgent issue to be solved is the utilization rate of raw materials. It is understood that leading companies such as Tianke and Tianyue are facing such problems. A crystal ingot is put into 4~5kg of silicon carbide polycrystalline raw materials, and only about 1kg of crystals that meet the processing and cutting requirements are grown, and the raw material utilization rate is only about 20%~25%. The current process uses 4~5kg of silicon carbide polycrystalline raw materials with a particle size of 8~20 meshes to be placed in the graphite crucible raw material domain for growth.

[0004] Taking the raw material domain height of 130mm as an example, the bottom of the raw material domain is the 0mm point. There are radial and longitudinal temperature gradients in the raw material domain. The upper and middle parts of the raw material are in the low temperature zone of the raw material domain (2250~2290℃), and the lower and middle parts of the raw material domain are in the high temperature zone (2290~2310℃). The longitudinal temperature gradient difference is 30~60℃. During the constant temperature crystal growth process, the raw material in the high temperature zone of 0~65mm in the lower and middle parts of the raw material domain is always sublimated. Due to the temperature gradient, it sublimates to the low temperature zone of 65~130mm in the raw material, and part of it is recrystallized into silicon carbide polycrystals. At the top of the raw material domain, part of it is sublimated to the surface of the seed crystal to form a silicon carbide single crystal. Since the lower and middle parts of the raw material domain are always in the high temperature zone, this part of the raw material is completely consumed during the crystal growth process. The upper and middle parts are always recrystallized due to the temperature gradient, so the raw material in the upper and middle parts is not used.

[0005] If the raw material domain is too high, for example, the loading height is greater than 130mm, the path of gas-phase silicon carbide transmission to the seed crystal will be elongated, and most of the gas-phase raw materials cannot reach the seed crystal end; if the raw material domain is too short, for example, less than 90mm, there will still be a longitudinal temperature gradient, and the bottom raw material supply will be insufficient in the later stage.

[0006] Therefore, in order to ensure the crystal thickness and quality, the raw material loading height must be kept between 90 and 130 mm, but the raw material utilization rate is only 20% to 25%, resulting in the problem of too low raw material utilization rate. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for recycling secondary raw materials of silicon carbide, which solves the problem of low raw material utilization rate.

[0008] The technical solution of the present invention is: a method for recycling silicon carbide secondary raw materials, in which the crucible moves downward at -0.5~-1mm / h in the second half of the crystal growth process, so as to achieve the purpose of utilizing the raw materials in the upper half of the raw material domain.

[0009] Furthermore, the recrystallized silicon carbide polycrystals and unused secondary raw materials are collected and processed for secondary utilization.

[0010] Furthermore, the recrystallized silicon carbide polycrystals are collected and crushed into 8-20 mesh for secondary utilization. The specific process includes: collecting the upper part of the raw materials in the raw material domain, performing the first screening, collecting the 8-20 mesh secondary raw materials and washing them, putting the silicon carbide polycrystalline blocks into a ball mill using a polytetrafluoroethylene ball mill jar, repeatedly grinding them in forward and reverse directions, and then using an inspection screening machine to screen out 8-20 mesh, washing and drying them for standby use.

[0011] Furthermore, the forward and reverse grinding is repeated multiple times as follows: forward rotation 110-130 r / min, reverse rotation 110-130 r / min, forward rotation 25-35 min, reverse rotation 25-35 min, and then rest for 4-8 min, and repeat 3 cycles.

[0012] Furthermore, the prepared secondary raw materials are selected for loading processing, so that the secondary recycled raw materials can be used for normal crystal growth.

[0013] Furthermore, with a loading height of 130mm, the bottom of the crucible is the 0mm point of the raw material domain; the processed secondary 8~20 mesh raw materials are loaded into the raw material domain from 0 to 55mm. This part of the raw materials comes from the top of the previous crystal growth raw material domain. This part is rich in silicon, C:Si=1:1.5~2, and this part is defined as the first raw material layer; continue to load 55~65mm of C powder to balance the carbon-silicon ratio, and this part is defined as the second raw material layer; the first raw material layer is sublimated to the second raw material layer after high temperature, and the excess silicon atoms will combine with the carbon atoms in the second raw material layer to form 1:1 silicon carbide, which reaches the seed crystal end to form a silicon carbide single crystal; continue to load new 8~20 mesh raw materials, with a height of 65~130mm, which is defined as the third raw material layer; put it into the cavity to start the process for crystal growth.

[0014] The beneficial effects of the present invention are:

[0015] 1. Raw materials in the low-temperature area of ​​the raw material domain can be used in the high-temperature area as the crucible moves downward, increasing the share of available raw materials;

[0016] 2. After crystal growth, the polycrystalline blocks on the surface of the raw material domain can be processed into 8~20 mesh raw materials for secondary utilization.

[0017] 3. Through a special loading method, the imbalance of carbon-silicon ratio of secondary raw materials can be solved, and the raw materials can be used repeatedly. DETAILED DESCRIPTION

[0018] Example 1

[0019] This embodiment discloses a method for recycling secondary raw materials of silicon carbide. In the second half of the crystal growth process, the crucible moves downward at -0.5~-1mm / h, so as to achieve the purpose of utilizing the raw materials in the upper half of the raw material domain. During the crystal growth process of the raw material domain, the 0~65mm part is always in the high temperature zone. The raw materials consumed in the crystal growth process mainly come from this part. The crystal growth process is between 80~120h. After 40h in the second half of the crystal growth, the supply of this part of raw materials gradually decreases.

[0020] Example 2

[0021] In addition to Example 1, the present embodiment also collects and processes the recrystallized and unused secondary raw materials, and processes them to achieve the purpose of secondary utilization. After the crystal growth is completed, there will be some recrystallized silicon carbide polycrystals on the surface of the raw material domain. This part of the raw material is rich in silicon, so this piece of silicon carbide polycrystal is collected and crushed to 8~20 mesh for secondary utilization. The specific process includes collecting the upper part of the raw material domain, performing the first screening, collecting 8~20 mesh secondary raw materials and washing them (ultrapure water), and using a polytetrafluoroethylene ball mill to put the silicon carbide polycrystalline block into a ball mill, rotating forward at 120r / min, reverse at 120r / min, rotating forward for 30min, reverse for 30min, and then resting for 5min to prevent the equipment from overheating. Repeat 3 cycles, and use an inspection screening machine to screen out 8~20 mesh for cleaning and drying for standby use.

[0022] Example 3

[0023] In addition to Examples 1 and 2, the prepared secondary raw materials are also selected for loading processing in this embodiment, so that the secondary recycled raw materials can be used for normal crystal growth. Let's take the loading height of 130mm and the bottom of the crucible as the 0mm point of the raw material domain as an example. The processed secondary 8~20 mesh raw materials are loaded into the raw material domain 0~55mm. This part of the raw materials comes from the top of the previous crystal growth raw material domain. This part is silicon-rich, C:Si=1:1.5~2, and this part is defined as the first raw material layer. Continue to load 55~65mm and load C powder to balance the carbon-silicon ratio. This part is defined in the second raw material layer. The first raw material layer is sublimated to the second raw material layer after high temperature. The excess silicon atoms will combine with the carbon atoms in the second raw material layer to form 1:1 silicon carbide, and reach the seed crystal end to form a silicon carbide single crystal. Continue to load new 8~20 mesh raw materials, with a height of 65~130mm, which is defined as the third raw material layer. Put it into the cavity to start the process for crystal growth.

[0024] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recycling silicon carbide secondary raw materials, characterized in that: In the second half of the crystal growth process, the crucible moves downward at -0.5~-1mm / h, so as to achieve the purpose of utilizing the raw materials in the upper half of the raw material area.

2. The method for recycling silicon carbide secondary raw materials according to claim 1, characterized in that: Collect and process recrystallized silicon carbide polycrystals and unused secondary raw materials for secondary processing.

3. The method for recycling silicon carbide secondary raw materials according to claim 2, characterized in that: The recrystallized silicon carbide polycrystals are collected and crushed into 8-20 mesh for secondary utilization. The specific process includes: collecting the upper part of the raw materials in the raw material field, performing the first screening, collecting the 8-20 mesh secondary raw materials and washing them, using a polytetrafluoroethylene ball mill jar, putting the silicon carbide polycrystalline block into a ball mill, repeatedly grinding it in forward and reverse directions, and then using an inspection screening machine to screen out 8-20 mesh for washing and drying for standby use.

4. The method for recycling silicon carbide secondary raw materials according to claim 3, characterized in that: The forward and reverse repeated grinding is specifically as follows: forward rotation 110-130 r / min, reverse rotation 110-130 r / min, forward rotation 25-35 min, reverse rotation 25-35 min, and then rest for 4-8 min, and repeat 3 cycles.

5. The method for recycling silicon carbide secondary raw materials according to claim 2 or 3, characterized in that: The prepared secondary raw materials are selected for loading processing so that the secondary recycled raw materials can be used for normal crystal growth.

6. The method for recycling silicon carbide secondary raw materials according to claim 5, characterized in that: With a loading height of 130mm, the bottom of the crucible is the 0mm point of the raw material domain; the processed secondary 8~20 mesh raw materials are loaded into the raw material domain from 0 to 55mm. This part of the raw materials comes from the top of the previous crystal growth raw material domain. This part is rich in silicon, C:Si=1:1.5~2, and this part is defined as the first raw material layer; continue to load 55~65mm of C powder to balance the carbon-silicon ratio, and this part is defined as the second raw material layer; the first raw material layer is sublimated to the second raw material layer after high temperature, and the excess silicon atoms will combine with the carbon atoms in the second raw material layer to form 1:1 silicon carbide, which reaches the seed crystal end to form a silicon carbide single crystal; continue to load new 8~20 mesh raw materials, with a height of 65~130mm, which is defined as the third raw material layer; put it into the cavity to start the process for crystal growth.