CN117966264A - Method for preparing high-purity silicon carbide by chemical vapor deposition - Google Patents
Method for preparing high-purity silicon carbide by chemical vapor deposition Download PDFInfo
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- CN117966264A CN117966264A CN202410150732.2A CN202410150732A CN117966264A CN 117966264 A CN117966264 A CN 117966264A CN 202410150732 A CN202410150732 A CN 202410150732A CN 117966264 A CN117966264 A CN 117966264A
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- 238000000034 method Methods 0.000 title claims abstract description 62
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 54
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 44
- 238000005229 chemical vapour deposition Methods 0.000 title claims abstract description 27
- 239000007789 gas Substances 0.000 claims abstract description 117
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 63
- 239000001257 hydrogen Substances 0.000 claims abstract description 63
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 60
- JLUFWMXJHAVVNN-UHFFFAOYSA-N methyltrichlorosilane Chemical compound C[Si](Cl)(Cl)Cl JLUFWMXJHAVVNN-UHFFFAOYSA-N 0.000 claims abstract description 59
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims abstract description 55
- IXCSERBJSXMMFS-UHFFFAOYSA-N hydrogen chloride Substances Cl.Cl IXCSERBJSXMMFS-UHFFFAOYSA-N 0.000 claims abstract description 55
- 229910000041 hydrogen chloride Inorganic materials 0.000 claims abstract description 55
- 238000002386 leaching Methods 0.000 claims abstract description 50
- 238000006243 chemical reaction Methods 0.000 claims abstract description 48
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 46
- 239000007788 liquid Substances 0.000 claims abstract description 43
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 40
- KOPOQZFJUQMUML-UHFFFAOYSA-N chlorosilane Chemical class Cl[SiH3] KOPOQZFJUQMUML-UHFFFAOYSA-N 0.000 claims abstract description 39
- 239000002994 raw material Substances 0.000 claims abstract description 37
- 238000001179 sorption measurement Methods 0.000 claims abstract description 36
- 238000001816 cooling Methods 0.000 claims abstract description 34
- 230000005587 bubbling Effects 0.000 claims abstract description 33
- 239000005055 methyl trichlorosilane Substances 0.000 claims abstract description 28
- 239000012535 impurity Substances 0.000 claims abstract description 22
- 150000002431 hydrogen Chemical class 0.000 claims abstract description 20
- 238000000746 purification Methods 0.000 claims abstract description 17
- 238000002156 mixing Methods 0.000 claims abstract description 6
- 239000003507 refrigerant Substances 0.000 claims abstract description 6
- 230000008016 vaporization Effects 0.000 claims abstract description 6
- VXEGSRKPIUDPQT-UHFFFAOYSA-N 4-[4-(4-methoxyphenyl)piperazin-1-yl]aniline Chemical compound C1=CC(OC)=CC=C1N1CCN(C=2C=CC(N)=CC=2)CC1 VXEGSRKPIUDPQT-UHFFFAOYSA-N 0.000 claims description 44
- 239000005049 silicon tetrachloride Substances 0.000 claims description 44
- ZDHXKXAHOVTTAH-UHFFFAOYSA-N trichlorosilane Chemical compound Cl[SiH](Cl)Cl ZDHXKXAHOVTTAH-UHFFFAOYSA-N 0.000 claims description 39
- 239000005052 trichlorosilane Substances 0.000 claims description 39
- 239000005046 Chlorosilane Substances 0.000 claims description 38
- 150000001335 aliphatic alkanes Chemical class 0.000 claims description 36
- 238000007740 vapor deposition Methods 0.000 claims description 23
- 238000009835 boiling Methods 0.000 claims description 18
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 10
- 238000005137 deposition process Methods 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
- 239000012159 carrier gas Substances 0.000 claims description 9
- 239000002826 coolant Substances 0.000 claims description 8
- FAQYAMRNWDIXMY-UHFFFAOYSA-N trichloroborane Chemical compound ClB(Cl)Cl FAQYAMRNWDIXMY-UHFFFAOYSA-N 0.000 claims description 7
- 239000002253 acid Substances 0.000 claims description 6
- 239000000498 cooling water Substances 0.000 claims description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 5
- 229910052751 metal Inorganic materials 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 239000001301 oxygen Substances 0.000 claims description 5
- 229910052760 oxygen Inorganic materials 0.000 claims description 5
- 229920006395 saturated elastomer Polymers 0.000 claims description 5
- 239000000126 substance Substances 0.000 claims description 5
- 239000002184 metal Substances 0.000 claims description 4
- 229910001510 metal chloride Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 2
- 239000011574 phosphorus Substances 0.000 claims description 2
- 238000000926 separation method Methods 0.000 claims description 2
- 239000004065 semiconductor Substances 0.000 abstract description 3
- 239000000463 material Substances 0.000 description 30
- 238000000151 deposition Methods 0.000 description 28
- 230000008021 deposition Effects 0.000 description 27
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- YGZSVWMBUCGDCV-UHFFFAOYSA-N chloro(methyl)silane Chemical compound C[SiH2]Cl YGZSVWMBUCGDCV-UHFFFAOYSA-N 0.000 description 7
- 238000002360 preparation method Methods 0.000 description 7
- 238000001514 detection method Methods 0.000 description 6
- 238000005245 sintering Methods 0.000 description 6
- 239000013078 crystal Substances 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000011863 silicon-based powder Substances 0.000 description 5
- 239000000969 carrier Substances 0.000 description 4
- 238000003795 desorption Methods 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000005265 energy consumption Methods 0.000 description 3
- 238000001036 glow-discharge mass spectrometry Methods 0.000 description 3
- 230000005484 gravity Effects 0.000 description 3
- 238000001308 synthesis method Methods 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- 229910052796 boron Inorganic materials 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- NEHMKBQYUWJMIP-UHFFFAOYSA-N chloromethane Chemical compound ClC NEHMKBQYUWJMIP-UHFFFAOYSA-N 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 208000012839 conversion disease Diseases 0.000 description 2
- 238000000407 epitaxy Methods 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
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- 239000012495 reaction gas Substances 0.000 description 2
- 238000007086 side reaction Methods 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910002601 GaN Inorganic materials 0.000 description 1
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 1
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- 239000003480 eluent Substances 0.000 description 1
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- 238000004949 mass spectrometry Methods 0.000 description 1
- 238000001819 mass spectrum Methods 0.000 description 1
- UIUXUFNYAYAMOE-UHFFFAOYSA-N methylsilane Chemical compound [SiH3]C UIUXUFNYAYAMOE-UHFFFAOYSA-N 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- FAIAAWCVCHQXDN-UHFFFAOYSA-N phosphorus trichloride Chemical compound ClP(Cl)Cl FAIAAWCVCHQXDN-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention relates to the technical field of semiconductors, in particular to a method for preparing high-purity silicon carbide by chemical vapor deposition, which comprises the following steps: (1) Rectifying and purifying raw material methyl trichlorosilane to ensure that the purity of the raw material methyl trichlorosilane is more than 99.99 percent and the impurity content is lower than 5ppm; (2) Mixing and vaporizing the purified monomethyl trichlorosilane and hydrogen, and then carrying out reaction; (3) Cooling the tail gas after reaction to room temperature, pressurizing to 0.6-1.0 MPa, exchanging heat with a refrigerant, further cooling to-40 ℃ to form condensate, sending the condensate into a rectification and purification process, and separating to obtain high-purity monomethyl trichlorosilane; (4) Sending the uncondensed tail gas in the step (3) to bubbling leaching, distilling and separating, and separating hydrogen chloride from the adsorbed saturated chlorosilane liquid; (5) The tail gas after bubbling and leaching is subjected to pressure swing adsorption by active carbon, and high-purity hydrogen is separated.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to a method for preparing high-purity silicon carbide by chemical vapor deposition.
Background
Silicon carbide single crystal Substrates (SiC) are third generation compound semiconductor materials, and compound materials composed of two elements of carbon and silicon are mainly divided into conductive type and semi-insulating type, wherein the conductive silicon carbide substrates (silicon carbide epitaxy) are mainly used for manufacturing high-power devices with high temperature resistance and high voltage resistance, and are widely applied to the fields of electronic power, such as new energy automobiles, photovoltaics, smart grids, rail transit and the like, and the market scale is larger; in addition, the semi-insulating silicon carbide substrate (gallium nitride epitaxy) is mainly applied to the fields of filtering radio frequency devices and the like, such as a power amplifier in 5G communication, a radio detector in national defense and the like, and along with the acceleration construction of a 5G communication network, market demands are obviously improved.
The main preparation method of the silicon carbide single crystal material is PVT (physical vapor transport method), and high-purity silicon carbide powder is used as a raw material to grow silicon carbide single crystals, so that a silicon carbide single crystal substrate is obtained. At present, four methods for preparing high-purity silicon carbide powder are mainly adopted: chemical Vapor Deposition (CVD), plasma, sol-gel, self-propagating high temperature synthesis, which is the main synthesis of silicon carbide powder worldwide and is the most well-established in current use.
A well-established method for global silicon carbide enterprises is a self-propagating high-temperature synthesis method. The improved self-propagating high-temperature synthesis process of silicon carbide powder adopts high-purity silicon powder and high-purity carbon powder as raw materials, and is sintered in high-temperature sintering furnace, and the temperature is controlled to be 1800-2000 deg.C, and the high-purity silicon carbide synthesized powder is finally obtained. The defects of the silicon carbide powder prepared by the method are obvious, firstly, raw material silicon powder and carbon powder need to be pretreated, and meanwhile, impurities in the powder can be completely transferred into the silicon carbide powder, so that the purity of the silicon carbide powder is completely limited by the purity of the silicon powder and the carbon powder, and even new impurities can be introduced in the pretreatment process. Secondly, the sintering process needs to maintain a high-temperature state for a long time, the reaction time is long, the yield is low, and the current single-furnace sintering yield is only 100-150kg. Then, problems of incomplete reaction or excessive carbon are liable to occur in the sintering process, and further removal of carbon is required. In addition, the sintering reaction needs to use high-purity auxiliary materials such as a graphite crucible, a thermal insulation felt and the like, impurities are easy to bring in, and the loss of graphite parts is large, so that the preparation cost of the silicon carbide powder is high.
In a comprehensive view, the existing self-propagating synthetic silicon carbide powder has the defects of limited raw material purity, easiness in introducing impurities in the process, difficulty in reaching more than 6N, insufficient carbon excess in sintering, large consumption of auxiliary materials such as graphite pieces and high operation energy consumption, so that the preparation cost of the high-purity silicon carbide powder is high.
Disclosure of Invention
The invention aims to provide a method for preparing high-purity silicon carbide by chemical vapor deposition, which greatly improves the purity of raw materials and the utilization rate of the raw materials, obtains a product with higher purity, reduces the energy consumption in the high-temperature chemical vapor deposition process and improves the reaction efficiency.
Based on the above purpose, the invention adopts the following technical scheme:
a method for preparing high purity silicon carbide by chemical vapor deposition, comprising the following steps:
(1) Rectifying and purifying raw material methyl trichlorosilane to ensure that the purity of the raw material methyl trichlorosilane is more than 99.99 percent and the impurity content is lower than 5ppm;
(2) Mixing and vaporizing the purified monomethyl trichlorosilane in the step (1) and hydrogen according to the mol ratio of 1:2-20, and then introducing the mixture into a vapor deposition furnace for reaction;
(3) The main components of the tail gas after the reaction in the step (2) are monomethyl trichlorosilane, hydrogen chloride, trichlorosilane, silicon tetrachloride and alkane, the tail gas after the reaction is cooled to room temperature, then pressurized to 0.6-1.0 MPa, and exchanges heat with a refrigerant, the tail gas is further cooled to-38 to-42 ℃, part of the tail gas is liquefied to form condensate, the main components of the condensate are monomethyl trichlorosilane and part of the trichlorosilane and the silicon tetrachloride, the condensate is heated to normal temperature through heat exchange, and then the condensate is sent to a rectification purification process, and the high-purity monomethyl trichlorosilane is obtained through separation and is continuously used as a raw material of vapor deposition reaction;
(4) Sending uncondensed tail gas in the step (3) into a bubbling leaching process, wherein the uncondensed tail gas is hydrogen, hydrogen chloride, trichlorosilane, silicon tetrachloride and alkane, the bubbling leaching liquid is chlorosilane liquid, the liquid temperature is minus 36 ℃, the trichlorosilane, the silicon tetrachloride and the hydrogen chloride in the tail gas are bubbled and leached in the chlorosilane leaching liquid and are adsorbed, the adsorbed liquid is distilled and separated, the hydrogen chloride adsorbed in the chlorosilane is desorbed, the separated hydrogen chloride can be used for preparing acid or used for hydrogenating the silicon tetrachloride, and the separated chlorosilane liquid is continuously used as the bubbling leaching liquid;
(5) The main components of the tail gas after bubbling and leaching are hydrogen, partial hydrogen chloride and alkane, and then the tail gas enters active carbon for pressure swing adsorption, hydrogen chloride and alkane in the tail gas can be adsorbed, high-purity hydrogen is separated out and is continuously used as carrier gas for chemical vapor deposition reaction, after the active carbon is saturated in adsorption, hydrogen chloride, alkane and the like can be desorbed through depressurization, and then the hydrogen chloride, the alkane and the like are hydrolyzed, neutralized or combusted.
Preferably, in the step (1), the rectification and purification are carried out by adopting a mode of connecting two towers in series, wherein the rectification tower firstly removes heavy weight and then removes light weight, the high-boiling point in the raw material of the monomethyl trichlorosilane is mainly metal chloride and phosphide with the boiling point of hundreds to thousands of ℃ and the low-boiling point is mainly boron chloride, trichlorosilane and silicon tetrachloride, the raw material of the monomethyl trichlorosilane enters from the tower 1, and the high-boiling point is discharged from the tower kettle, so that metal and phosphorus impurities are reduced; the methyl trichlorosilane extracted from the tower top of the 1 tower enters the 2 tower together with a small amount of trichlorosilane and silicon tetrachloride, the low-boiling-point substances are extracted from the tower top of the 2 tower, the boron chloride, the trichlorosilane and the silicon tetrachloride are separated, and the high-purity methyl trichlorosilane is produced from the tower bottom.
Preferably, in step (2), the hydrogen gas has a purity of greater than 5N, a dew point of < -60 ℃, a nitrogen content of less than 2ppm in the hydrogen gas, and an oxygen content of less than 4ppm.
Preferably, the vapor deposition reaction temperature in the step (2) is 1200-1600 ℃, and the deposition process pressure is normal pressure to 6bar.
Preferably, the vapor deposition reaction temperature in the step (2) is 1400-1500 ℃ and the deposition process pressure is 0.5-1.5bar.
Preferably, in the step (3), the specific process of cooling to room temperature is as follows: the exhaust gas temperature of the vapor deposition reaction is 300-500 ℃, the exhaust gas is subjected to primary cooling, the temperature is reduced to 200-350 ℃ by heat exchange with normal-temperature cooling water, then the exhaust gas is subjected to secondary heat exchange in a tube type heat exchanger to be reduced to be lower than 200 ℃, then the exhaust gas is subjected to tertiary cooling, the temperature of the exhaust gas can be reduced to be lower than 40 ℃ by taking the normal-temperature water as a cooling medium, and condensate is generated; and (3) the cryogenic cooling is that after the tail gas cooled to the temperature within 40 ℃ is pressurized to 6-10bar, the tail gas is subjected to secondary cooling in a tube type heat exchanger, the tail gas is cooled to-38 to-42 ℃ in a cryogenic way, condensate is further generated, the heat exchange medium is freon, the temperature is-60 ℃, and at the moment, the condensate component mainly comprises methyltrichlorosilane, a small amount of trichlorosilane and silicon tetrachloride.
Preferably, in the step (3), the condensate cooled to the temperature of minus 38 ℃ to minus 42 ℃ is subjected to primary heat exchange with tail gas in a shell and tube heat exchanger to raise the temperature from minus 40 ℃ to 0 ℃ to 5 ℃, then is subjected to secondary heat exchange with normal-temperature water medium in the shell and tube heat exchanger to raise the temperature to 10 ℃ to 20 ℃, and then the condensate is sent to a purification process to remove trichlorosilane and silicon tetrachloride, so that the monomethyl trichlorosilane is obtained.
Preferably, in the bubbling leaching process of the step (4), the adopted leaching solution is chlorosilane liquid, the chlorosilane liquid can be trichlorosilane or silicon tetrachloride, the tail gas pressure is 5-8bar, the pressure of a leaching tower is controlled to be 3-5 bar, and the temperature of the leaching solution is-34 to-38 ℃.
Preferably, in the step (5), the gas which is not absorbed in the tail gas after bubbling and leaching is mainly hydrogen, alkane, chlorosilane and hydrogen chloride, and the active carbon adsorption column is adopted to adsorb the rest components except the hydrogen, so as to obtain the high-purity hydrogen.
Preferably, the three activated carbon adsorption columns in the adsorption process are a group, each activated carbon adsorption column alternately and circularly works under the control of a time program to adsorb, regenerate and cool respectively, the temperature is 45-50 ℃ and the pressure is 0.4-0.6 MPa in the adsorption process, and after the activated carbon adsorbs trace chlorosilane, hydrogen chloride and alkane in the hydrogen, carbon powder is filtered to obtain high-purity hydrogen.
The adsorption column used in the invention is columnar active carbon, wherein the active carbon with the granularity of 4-12 meshes accounts for more than 93 percent, and the bulk specific gravity is 0.48-0.52g/ml.
The raw material of the methyl trichlorosilane used in the invention is industrial grade purity of more than 99.9 percent, which is an important byproduct of the direct synthesis method for preparing the organic silicon monomer, and because the raw material used in the direct synthesis method is chloromethane and silicon powder, metal in the silicon powder and B, P impurities also directly react and remain in the material, and according to the current GB/T20434-2006 product standard of methyl trichlorosilane, the purity requirement of the methyl trichlorosilane does not contain metal elements and B, P elements. Therefore, the patent uses the monomethyl trichlorosilane as a raw material, and the impurities to be removed are metal chloride, boron chloride, phosphorus chloride, chlorosilane and the like. And purifying by using the boiling point difference of chloride, chlorosilane and monomethyl trichlorosilane and adopting a rectification purification process. In the purification, the high-boiling substances in the raw material monomethyl trichlorosilane (with the boiling point of 66 ℃) are mainly metal chlorides and phosphides (with the boiling point of hundreds to thousands of ℃ C.), and the low-boiling substances are mainly boron chloride (with the boiling point of 12 to 5 ℃), trichlorosilane (with the boiling point of 32 to 34 ℃), silicon tetrachloride (with the boiling point of 57 to 6 ℃), and the like. In the rectification and purification process, a mode of connecting 2 towers in series is adopted, heavy removal is performed first, then light removal is performed, materials enter from the middle part of the 1 tower, high-boiling residues are discharged from the tower kettle, and the purpose of reducing metal and P impurities is achieved. 1, extracting monomethyl trichlorosilane from the tower top, then entering the middle part of the 2 tower together with a small amount of trichlorosilane and silicon tetrachloride (from tail gas condensate), extracting low-boiling substances from the 2 tower top, and achieving the effect of separating components such as boron chloride, trichlorosilane and silicon tetrachloride, and the like, thereby producing a high-purity monomethyl trichlorosilane product from the tower bottom.
The hydrogen in the invention comes from two parts, the hydrogen source in the initial stage of system operation is electrolytic hydrogen production, after the system operation, the hydrogen in the tail gas can be recycled for feeding of the reactor after being recovered, and can be used as a main hydrogen source, and the electrolytic hydrogen production supplements a small amount of hydrogen in the replacement loss of the system; wherein, the monomethyl trichlorosilane is used as a reaction gas source to decompose and generate silicon carbide and hydrogen chloride, and a small amount of side reaction is accompanied, and the side reaction products are alkanes such as trichlorosilane, silicon tetrachloride, acetylene and the like. The hydrogen is a reaction gas source and is also used as a carrier gas, a part of the hydrogen participates in the decomposition reaction of the monomethyl silane, and a part of the hydrogen is used as the carrier gas to drive the mass transfer process of the material on the deposition surface.
In the invention, a bell-type reactor is adopted for vapor deposition reaction, a plurality of pairs of portal carriers are arranged in the reactor, a plurality of air inlets are arranged on a bottom plate of the reactor, the air inlets and the carriers are uniformly arranged, and a plurality of air outlets are arranged in the center of the bottom plate. The bottom plate and the bell of the bell-jar reactor are both of jacket structures, heat conduction oil or cooling water medium is introduced into the jacket to cool the bottom plate and the bell, the cooling medium absorbs heat and ensures that the inner walls of the bottom plate and the bell are always maintained at low temperature, and the inner walls of the reactor are ensured not to generate deposition reaction. The flow rate of the cooling medium has obvious relation according to the size of the furnace cylinder, the temperature of the carrier, the size of the carrier and the like, and 4 pairs of carriers are taken as an example, the surface temperature of the carrier is 1200 ℃, and the flow rate of the cooling medium is required to be more than 60 cubic/hour. In practice, the temperature of the inner wall is generally lower than 300 ℃, and the deposition reaction does not occur on the surface of the inner wall. In the reaction process, as the deposition layer becomes thicker, the surface area of the deposition layer also becomes larger, the monomethyl trichlorosilane and the hydrogen in the material can maintain a constant proportion, but the gas quantity and the surface area of the deposition layer need to be synchronously increased, and the larger the surface area of the deposition layer is, the larger the gas quantity is.
In the bubbling leaching process, chlorosilane serving as a spray liquid is called lean liquid, chlorosilane liquid with adsorbed hydrogen chloride is called rich liquid, and the rich liquid passes through a first-stage lean-rich liquid heat exchanger and a second-stage lean-rich liquid heat exchanger after coming out of the bottom of a leaching tower, is heated to 25-30 ℃, and then enters the middle part of a desorption tower. Hydrogen chloride is extracted from the top of the desorption tower and is used for preparing acid by hydrolysis, barren liquor is extracted from the bottom of the desorption tower, and is cooled to-36 ℃ after passing through a second-stage barren-rich liquor heat exchanger, a first-stage barren-rich liquor heat exchanger and a subcooler, and is circulated to the top of the leaching tower to be used as eluent. Wherein the temperature of the tower bottom of the desorption tower is 140 ℃, and the pressure of the tower top is 0.8MPa.
Compared with the prior art, the invention has the following beneficial effects:
The preparation method greatly improves the purity of the raw materials and the utilization rate of the raw materials, the purity of the obtained product is higher, and the components in the reaction tail gas are recovered and separated, particularly, the hydrogen and the methylchlorosilane raw materials are used as carrier gas, so that zero consumption is almost realized, and the methylchlorosilane can be completely used for reaction conversion.
The preparation method of the invention takes methyl chlorosilane containing carbon and silicon as raw materials, and can obtain high-purity methyl chlorosilane after rectification and purification, and the high-purity methyl chlorosilane is used for chemical vapor deposition of silicon carbide. The materials used by the method are easy to purify, the purifying method is simple, the impurity content of the purified materials is extremely low, the purity of the silicon carbide deposited by the method is 6-8N, the deposition layer is apparent and compact, the deposition layer has no defects such as holes and cracks, and the deposition thickness is 10-100mm.
The preparation method of the invention adopts a jacketed bell-jar reactor, a heat exchange medium is arranged in the jacket, the heat dissipated by the carrier can be circularly absorbed and recycled, the energy consumption in the high-temperature chemical vapor deposition process is reduced, the reactor is a bell-jar reactor and consists of a bell jar, a bottom plate and the carrier, the bottom plate is simultaneously provided with an air inlet and an air outlet, materials enter from the air inlet and can flow freely in a furnace chamber, the material gas can reach the surface of the carrier freely and carry out deposition reaction, and the reacted material gas flows out from the air outlet. The carrier is a heat source, the surface temperature of the carrier is required to be controlled to be maintained above 1200 ℃, and the temperature of the rest wall surface is obviously lower than the surface temperature of the carrier, so that the deposition reaction is ensured to occur only on the surface of the high-temperature carrier. The gas in the reactor can ensure the material quantity and the material concentration required by the deposition reaction, fresh materials are required to be consumed by the surface reaction of the carrier, reaction tail gas is generated, and the material quantity and the material concentration near the surface of the carrier can be kept constant, so that the deposition reaction can be stably carried out. (if the gas flows unidirectionally, the concentration of the material at the inlet is high, the concentration of the material at the outlet is low, the deposition difference is large, and the uniformity is poor. If the space of the reaction chamber is small, the concentration polarization condition can occur, the deposition difference is also large, and the uniformity is poor.) the invention has high deposition efficiency, and the deposition speed of silicon carbide in the deposition process can be always maintained to be more than 0.5mm/h, even higher, and by taking 4 pairs of carriers as an example, the carrier height is 2000mm, and the high-purity silicon carbide of more than 200kg can be prepared in 50 hours.
The preparation method of the invention can also recycle and separate each component in the reaction tail gas, especially hydrogen and methyl chlorosilane raw materials, the hydrogen is used as carrier gas, zero consumption is almost realized, and the methyl chlorosilane can be completely used for reaction conversion to produce silicon carbide, byproduct hydrogen chloride and a small amount of chlorosilane. And the method realizes full sealing in the transportation and conversion processes, the materials are not exposed to the environment in the whole process flow, and the method has the characteristic of high cleanliness, is not easy to introduce foreign impurities and other pollution, thereby affecting the purity of the silicon carbide material.
Drawings
FIG. 1 is a process flow diagram of a method of making the present invention;
figure 2 is an XRD pattern for a silicon carbide material obtained by vapor deposition in example 1 of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below, but the following embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, based on the examples of the invention, which a person skilled in the art would have without inventive effort, fall within the scope of the invention.
Example 1
A method for preparing high purity silicon carbide by chemical vapor deposition, comprising the following steps:
(1) Rectifying and purifying raw material methyl trichlorosilane to ensure that the purity of the raw material methyl trichlorosilane is more than 99.99 percent and the impurity content is lower than 5ppm; the rectification and purification in the step (1) are carried out, and a rectification tower adopts a mode of connecting two towers in series, and is firstly used for removing heavy weight and then light weight;
(2) Mixing and vaporizing the purified monomethyl trichlorosilane in the step (1) and hydrogen according to the mol ratio of 1:12, and then introducing the mixture into a vapor deposition furnace for reaction; the purity of the hydrogen is 5N, the dew point is-61 ℃, the nitrogen content in the hydrogen is less than 2ppm, the oxygen content is less than 4ppm, the vapor deposition reaction temperature is 1500 ℃, and the deposition process pressure is 1.0bar; the bell-jar type reactor internal equipment 4 is used for carrying a portal carrier with the height of 2000mm and the deposition time of 40 hours, the deposition speed of silicon carbide in the deposition process is always maintained above 0.5mm/h, and the deposition weight of SiC is 200kg;
(3) Cooling the reacted tail gas to room temperature, pressurizing to 0.8MPa, exchanging heat with a refrigerant, further cooling to-40 ℃ in a deep way, liquefying part of the tail gas to form condensate, wherein the main components of the condensate are methyl trichlorosilane and part of trichlorosilane and silicon tetrachloride, performing primary heat exchange and heating on the condensate and the tail gas in a shell and tube heat exchanger, heating the temperature to 3 ℃ from-40 ℃, performing secondary heat exchange and heating to 15 ℃ in the shell and tube heat exchanger with normal-temperature water medium, and then sending the condensate to a purification process to remove the trichlorosilane and the silicon tetrachloride to obtain the methyl trichlorosilane, and continuously serving as a raw material of vapor deposition reaction;
The concrete process of cooling to room temperature is as follows: the exhaust gas temperature of the vapor deposition reaction is 400 ℃, the exhaust gas temperature is firstly subjected to primary cooling, the temperature is reduced to 280 ℃ by heat exchange with normal-temperature cooling water, then the heat exchange is carried out with the feed mixed gas (about 100 ℃), the temperature is reduced to be lower than 200 ℃ by secondary heat exchange in a shell and tube heat exchanger, then the exhaust gas is subjected to tertiary cooling, the temperature of the exhaust gas can be reduced to be lower than 40 ℃ by taking the low-temperature water as a cooling medium, and condensate is generated;
The cryogenic cooling is that after the tail gas cooled to the temperature of less than 40 ℃ is pressurized to 7bar, the tail gas is subjected to secondary cooling in a tube type heat exchanger, the tail gas is further cooled to the temperature of minus 40 ℃ to generate condensate, the heat exchange medium is Freon, the temperature is minus 60 ℃, and at the moment, the condensate mainly comprises monomethyl trichlorosilane and a small amount of trichlorosilane and silicon tetrachloride;
(4) Sending uncondensed tail gas in the step (3) into a bubbling leaching process, wherein the uncondensed tail gas mainly comprises hydrogen, hydrogen chloride, trichlorosilane, silicon tetrachloride and alkane, the bubbling leaching liquid is chlorosilane liquid, the trichlorosilane, the silicon tetrachloride and the hydrogen chloride in the tail gas are bubbled and leached in the chlorosilane leaching liquid and are adsorbed, the adsorbed liquid is distilled and separated, hydrogen chloride adsorbed in the chlorosilane is desorbed, the separated hydrogen chloride can be used for preparing acid or for hydrogenating the silicon tetrachloride, and the separated chlorosilane liquid is continuously used as the bubbling leaching liquid; in the bubbling leaching process, the tail gas pressure is 6bar, the pressure of a leaching tower is controlled to be 4bar, and the temperature of leaching solution is-36 ℃.
(5) The main components of the tail gas after bubbling and leaching are hydrogen, partial hydrogen chloride and alkane, and then the tail gas enters active carbon for pressure swing adsorption, so that the hydrogen chloride and the alkane in the tail gas can be adsorbed, high-purity hydrogen is separated out and is continuously used as carrier gas for chemical vapor deposition reaction, after the active carbon is saturated in adsorption, the hydrogen chloride, the alkane and the like can be desorbed through depressurization, and then the hydrogen chloride, the alkane and the like are hydrolyzed and neutralized or combusted; in the tail gas after bubbling and leaching, the unabsorbed gas is mainly hydrogen, a small amount of alkane and trace chlorosilane and hydrogen chloride, and an activated carbon adsorption column is used for adsorbing impurities in the hydrogen; wherein the adsorption process comprises a group of three active carbon adsorption columns, each active carbon adsorption column alternately and circularly works under the control of a time program to respectively adsorb, regenerate and cool, the temperature is 47 ℃ and the pressure is 0.5MPa in the adsorption process, and after the active carbon adsorbs trace chlorosilane, hydrogen chloride and alkane in the hydrogen, carbon powder is filtered to obtain the hydrogen; the adsorption column is columnar activated carbon with granularity of 8 meshes, the proportion of the column is 94%, and the specific gravity of the column is 0.48g/ml.
Example 2
A method for preparing high purity silicon carbide by chemical vapor deposition, comprising the following steps:
(1) Rectifying and purifying raw material methyl trichlorosilane to ensure that the purity of the raw material methyl trichlorosilane is more than 99.99 percent and the impurity content is lower than 2ppm; the rectification and purification in the step (1) are carried out, and a rectification tower adopts a mode of connecting two towers in series, and is firstly used for removing heavy weight and then light weight;
(2) Mixing and vaporizing the purified monomethyl trichlorosilane in the step (1) and hydrogen according to the mol ratio of 1:2, and then introducing the mixture into a vapor deposition furnace for reaction; the purity of the hydrogen is 5N, the dew point is-63 ℃, the nitrogen content in the hydrogen is less than 2ppm, the oxygen content is less than 4ppm, the vapor deposition reaction temperature is 1200 ℃, the deposition process pressure is less than 6bar, and the optimal pressure is 0.5bar;
the bell-jar reactor internal equipment 4 is used for carrying a carrier in a shape like a Chinese character 'men', the height of the carrier is 2000mm, the deposition time is 50 hours, the deposition speed of silicon carbide in the deposition process is always maintained above 0.5mm/h, and the deposition weight of SiC is 250kg;
(3) Cooling the reacted tail gas to room temperature, pressurizing to 0.6MPa, exchanging heat with a refrigerant, further cooling to-42 ℃ in a deep way, liquefying part of the tail gas to form condensate, wherein the main components of the condensate are methyl trichlorosilane and part of trichlorosilane and silicon tetrachloride, performing primary heat exchange and heating on the condensate and the tail gas in a shell and tube heat exchanger, heating the temperature to 0 ℃ from-42 ℃, performing secondary heat exchange and heating to 10 ℃ in the shell and tube heat exchanger with normal-temperature water medium, and then sending the condensate to a purification process to remove the trichlorosilane and the silicon tetrachloride to obtain the methyl trichlorosilane, and continuously serving as a raw material of vapor deposition reaction;
The concrete process of cooling to room temperature is as follows: the exhaust gas temperature of the vapor deposition reaction is 300 ℃, the exhaust gas temperature is firstly subjected to primary cooling, the temperature is reduced to 200 ℃ by heat exchange with normal-temperature cooling water, then the heat exchange is carried out with the feed mixed gas (about 70 ℃), the temperature is reduced to be lower than 200 ℃ by secondary heat exchange in a shell and tube heat exchanger, then the exhaust gas is subjected to tertiary cooling, the temperature of the exhaust gas can be reduced to be lower than 40 ℃ by taking the low-temperature water as a cooling medium, and condensate is generated;
the cryogenic cooling is that after the tail gas cooled to the temperature of less than 40 ℃ is pressurized to 6bar, the tail gas is subjected to secondary cooling in a tube type heat exchanger, the tail gas is further cooled to-38 ℃ to generate condensate, the heat exchange medium is Freon, the temperature is-60 ℃, and at the moment, the condensate mainly comprises monomethyl trichlorosilane and a small amount of trichlorosilane and silicon tetrachloride;
(4) Sending uncondensed tail gas in the step (3) into a bubbling leaching process, wherein the uncondensed tail gas mainly comprises hydrogen, hydrogen chloride, trichlorosilane, silicon tetrachloride and alkane, the bubbling leaching liquid is chlorosilane liquid, the trichlorosilane, the silicon tetrachloride and the hydrogen chloride in the tail gas are bubbled and leached in the chlorosilane leaching liquid and are adsorbed, the adsorbed liquid is distilled and separated, hydrogen chloride adsorbed in the chlorosilane is desorbed, the separated hydrogen chloride can be used for preparing acid or for hydrogenating the silicon tetrachloride, and the separated chlorosilane liquid is continuously used as the bubbling leaching liquid; in the bubbling leaching process, the tail gas pressure is 5bar, the pressure of a leaching tower is controlled at 3bar, and the temperature of leaching solution is-34 ℃.
(5) The main components of the tail gas after bubbling and leaching are hydrogen, partial hydrogen chloride and alkane, and then the tail gas enters active carbon for pressure swing adsorption, so that the hydrogen chloride and the alkane in the tail gas can be adsorbed, high-purity hydrogen is separated out and is continuously used as carrier gas for chemical vapor deposition reaction, after the active carbon is saturated in adsorption, the hydrogen chloride, the alkane and the like can be desorbed through depressurization, and then the hydrogen chloride, the alkane and the like are hydrolyzed and neutralized or combusted; in the tail gas after bubbling and leaching, the unabsorbed gas is mainly hydrogen, a small amount of alkane and trace chlorosilane and hydrogen chloride, and an activated carbon adsorption column is used for adsorbing impurities in the hydrogen; wherein the adsorption process comprises a group of three active carbon adsorption columns, each active carbon adsorption column alternately and circularly works under the control of a time program to respectively adsorb, regenerate and cool, the temperature is 45 ℃ and the pressure is 0.4MPa in the adsorption process, and the active carbon filters carbon powder after adsorbing trace chlorosilane, hydrogen chloride and alkane in the hydrogen to obtain the hydrogen; the adsorption column is columnar active carbon with granularity of 12 meshes, the proportion of the active carbon is 96%, and the contrast proportion is 0.52g/ml.
Example 3
A method for preparing high purity silicon carbide by chemical vapor deposition, comprising the following steps:
(1) Rectifying and purifying raw material methyl trichlorosilane to ensure that the purity of the raw material methyl trichlorosilane is more than 99.99 percent and the impurity content is lower than 3ppm; the rectification and purification in the step (1) are carried out, and a rectification tower adopts a mode of connecting two towers in series, and is firstly used for removing heavy weight and then light weight;
(2) Mixing and vaporizing the purified monomethyl trichlorosilane in the step (1) and hydrogen according to the mol ratio of 1:20, and then introducing the mixture into a vapor deposition furnace for reaction; the purity of the hydrogen is 5N, the dew point is-64 ℃, the nitrogen content in the hydrogen is less than 2ppm, the oxygen content is less than 4ppm, the vapor deposition reaction temperature is 1600 ℃, the deposition process pressure is less than 6bar, and the optimal pressure is 1.5bar;
The bell-jar reactor internal equipment 4 is used for carrying a carrier in a shape like a Chinese character 'men', the height of the carrier is 2000mm, the deposition time is 30 hours, the deposition speed of silicon carbide in the deposition process is always maintained above 0.7mm/h, and the deposition weight of SiC is 200kg;
(3) Cooling the reacted tail gas to room temperature, pressurizing to 0.1MPa, exchanging heat with a refrigerant, further cooling to-38 ℃ in a deep way, liquefying part of the tail gas to form condensate, wherein the main components of the condensate are methyl trichlorosilane and part of trichlorosilane and silicon tetrachloride, performing primary heat exchange and heating on the condensate and the tail gas in a shell and tube heat exchanger, heating the temperature to 5 ℃ from-38 ℃, performing secondary heat exchange and heating to 20 ℃ in the shell and tube heat exchanger with normal-temperature water medium, and then sending the condensate to a purification process to remove the trichlorosilane and the silicon tetrachloride to obtain the methyl trichlorosilane, and continuously serving as a raw material of vapor deposition reaction;
The concrete process of cooling to room temperature is as follows: the exhaust gas temperature of the vapor deposition reaction is 500 ℃, the exhaust gas temperature is firstly subjected to primary cooling, the temperature is reduced to 350 ℃ by heat exchange with normal-temperature cooling water, then the heat exchange is carried out with the feed mixed gas (about 120 ℃), the temperature is reduced to be lower than 200 ℃ by secondary heat exchange in a shell and tube heat exchanger, then the exhaust gas is subjected to tertiary cooling, the temperature of the exhaust gas can be reduced to be lower than 40 ℃ by taking the low-temperature water as a cooling medium, and condensate is generated;
The cryogenic cooling is that after the tail gas cooled to the temperature of less than 40 ℃ is pressurized to 10bar, the tail gas is subjected to secondary cooling in a tube type heat exchanger, the tail gas is subjected to cryogenic cooling to the temperature of-42 ℃, condensate is further generated, the heat exchange medium is Freon, the temperature is-60 ℃, and at the moment, the condensate mainly comprises monomethyl trichlorosilane and a small amount of trichlorosilane and silicon tetrachloride;
(4) Sending uncondensed tail gas in the step (3) into a bubbling leaching process, wherein the uncondensed tail gas mainly comprises hydrogen, hydrogen chloride, trichlorosilane, silicon tetrachloride and alkane, the bubbling leaching liquid is chlorosilane liquid, the trichlorosilane, the silicon tetrachloride and the hydrogen chloride in the tail gas are bubbled and leached in the chlorosilane leaching liquid and are adsorbed, the adsorbed liquid is distilled and separated, hydrogen chloride adsorbed in the chlorosilane is desorbed, the separated hydrogen chloride can be used for preparing acid or for hydrogenating the silicon tetrachloride, and the separated chlorosilane liquid is continuously used as the bubbling leaching liquid; in the bubbling leaching process, the tail gas pressure is 5bar, the pressure of a leaching tower is controlled at 5bar, and the temperature of leaching solution is-38 ℃.
(5) The main components of the tail gas after bubbling and leaching are hydrogen, partial hydrogen chloride and alkane, and then the tail gas enters active carbon for pressure swing adsorption, so that the hydrogen chloride and the alkane in the tail gas can be adsorbed, high-purity hydrogen is separated out and is continuously used as carrier gas for chemical vapor deposition reaction, after the active carbon is saturated in adsorption, the hydrogen chloride, the alkane and the like can be desorbed through depressurization, and then the hydrogen chloride, the alkane and the like are hydrolyzed and neutralized or combusted; in the tail gas after bubbling and leaching, the unabsorbed gas is mainly hydrogen, a small amount of alkane and trace chlorosilane and hydrogen chloride, and an activated carbon adsorption column is used for adsorbing impurities in the hydrogen; wherein the adsorption process comprises a group of three active carbon adsorption columns, each active carbon adsorption column alternately and circularly works under the control of a time program to respectively adsorb, regenerate and cool, the temperature is 50 ℃ and the pressure is 0.6MPa in the adsorption process, and after the active carbon adsorbs trace chlorosilane, hydrogen chloride and alkane in the hydrogen, carbon powder is filtered to obtain the hydrogen; the adsorption column is columnar active carbon with granularity of 4 meshes, the proportion of the active carbon is 95%, and the specific gravity of the active carbon is 0.5g/ml.
After raw material monomethyl trichlorosilane in the embodiments 1-3 is rectified and purified, according to a detection method in GB/T20434-2006 standard, GC detection results show that the purity of the monomethyl trichlorosilane is more than 99.99%, and ICP-MS (mass spectrum) results show that the total content of impurities in the monomethyl trichlorosilane is less than 5ppm. The results are shown in Table 1.
TABLE 1 mass spectrometry detection results for examples 1-3
The silicon carbide material obtained by depositing in the embodiment 1 of the invention is sampled, XRD detection is carried out, sampling positions are respectively positioned at the upper part, the middle part and the lower part of the carrier, an X-ray powder diffraction method is adopted to analyze the material components in the silicon carbide material, the result shows that only SiC in a 3C crystal form is provided, other diffraction peaks such as Si, C and the like are avoided, the excessive carbon or silicon is not contained in the silicon carbide material, and the detection result is shown in the figure 1.
The silicon carbide material deposited by the method is detected by GDMS (glow discharge mass spectrometry), so that the trace element content in a solid sample can be directly detected. The test object was a silicon carbide deposited layer of the silicon carbide material obtained in example 1, and the test elements and contents are shown in Table 2, and the total impurity content was 1ppm.
TABLE 2 GDMS detection of the deposited layer of silicon carbide material of EXAMPLE 1
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.
Claims (8)
1. A method for preparing high-purity silicon carbide by chemical vapor deposition, which is characterized by comprising the following steps:
(1) Rectifying and purifying raw material methyl trichlorosilane to ensure that the purity of the raw material methyl trichlorosilane is more than 99.99 percent and the impurity content is lower than 5ppm;
(2) Mixing and vaporizing the purified monomethyl trichlorosilane in the step (1) and hydrogen according to the mol ratio of 1:2-20, and then introducing the mixture into a vapor deposition furnace for reaction;
(3) The main components of the tail gas after the reaction in the step (2) are monomethyl trichlorosilane, hydrogen chloride, trichlorosilane, silicon tetrachloride and alkane, the tail gas after the reaction is cooled to room temperature, then pressurized to 0.6-1.0 MPa, and exchanges heat with a refrigerant, the tail gas is further cooled to-38 to-42 ℃, part of the tail gas is liquefied to form condensate, the main components of the condensate are monomethyl trichlorosilane and part of the trichlorosilane and the silicon tetrachloride, the condensate is heated to normal temperature through heat exchange, and then the condensate is sent to a rectification purification process, and the high-purity monomethyl trichlorosilane is obtained through separation and is continuously used as a raw material of vapor deposition reaction;
(4) Sending uncondensed tail gas in the step (3) into a bubbling leaching process, wherein the uncondensed tail gas mainly comprises hydrogen, hydrogen chloride, trichlorosilane, silicon tetrachloride and alkane, the bubbling leaching liquid is chlorosilane liquid, the trichlorosilane, the silicon tetrachloride and the hydrogen chloride in the tail gas are bubbled and leached in the chlorosilane leaching liquid and are adsorbed, the adsorbed liquid is distilled and separated, hydrogen chloride adsorbed in the chlorosilane is desorbed, the separated hydrogen chloride can be used for preparing acid or for hydrogenating the silicon tetrachloride, and the separated chlorosilane liquid is continuously used as the bubbling leaching liquid;
(5) The main components of the tail gas after bubbling and leaching are hydrogen, partial hydrogen chloride and alkane, and then the tail gas enters active carbon for pressure swing adsorption, so that the hydrogen chloride and the alkane in the tail gas can be adsorbed, high-purity hydrogen is separated out and is continuously used as carrier gas for chemical vapor deposition reaction, and after the active carbon is saturated in adsorption, the hydrogen chloride and the alkane can be desorbed through depressurization, and then are hydrolyzed, neutralized or combusted.
2. The method for preparing high-purity silicon carbide by chemical vapor deposition according to claim 1, wherein in the step (1), rectification and purification are carried out, a rectification tower adopts a mode of two towers connected in series, heavy removal is carried out firstly, then light removal is carried out, high boiling point in raw material methyl trichlorosilane mainly comprises metal chlorides and phosphide with boiling points of hundreds to thousands of ℃ and low boiling point mainly comprises boron chloride, trichlorosilane and silicon tetrachloride, raw material methyl trichlorosilane enters from a tower 1, high boiling point is discharged from a tower kettle, and metal and phosphorus impurities are reduced; the methyl trichlorosilane extracted from the tower top of the 1 tower enters the 2 tower together with a small amount of trichlorosilane and silicon tetrachloride, the low-boiling-point substances are extracted from the tower top of the 2 tower, the boron chloride, the trichlorosilane and the silicon tetrachloride are separated, and the high-purity methyl trichlorosilane is produced from the tower bottom.
3. The method for producing high purity silicon carbide by chemical vapor deposition according to claim 1, wherein in step (2), the purity of the hydrogen gas is more than 5N, the dew point is < -60 ℃, the nitrogen content in the hydrogen is less than 2ppm, and the oxygen content is less than 4ppm.
4. The method for preparing high purity silicon carbide by chemical vapor deposition according to claim 1, wherein the vapor deposition reaction temperature in the step (2) is 1200 ℃ to 1600 ℃ and the deposition process pressure is normal pressure to 6bar.
5. The method for preparing high purity silicon carbide by chemical vapor deposition according to claim 1, wherein in the step (3), the specific process of cooling to room temperature is: the exhaust gas temperature of the vapor deposition reaction is 300-500 ℃, the exhaust gas is subjected to primary cooling, the temperature is reduced to 200-350 ℃ by heat exchange with normal-temperature cooling water, then the exhaust gas is subjected to secondary heat exchange in a tube type heat exchanger to be reduced to be lower than 200 ℃, then the exhaust gas is subjected to tertiary cooling, the temperature of the exhaust gas can be reduced to be lower than 40 ℃ by taking the normal-temperature water as a cooling medium, and condensate is generated; and (3) the cryogenic cooling is that after the tail gas cooled to the temperature within 40 ℃ is pressurized to 6-10bar, the tail gas is subjected to secondary cooling in a tube type heat exchanger, the tail gas is cooled to-38 to-42 ℃ in a cryogenic way, condensate is generated, the heat exchange medium is freon, the temperature is-60 ℃, and at the moment, the condensate component mainly comprises monomethyl trichlorosilane, a small amount of trichlorosilane and silicon tetrachloride.
6. The method for preparing high-purity silicon carbide by chemical vapor deposition according to claim 1, wherein in the step (3), the condensate which is cooled to-38 to-42 ℃ is subjected to primary heat exchange with tail gas in a tube type heat exchanger to raise the temperature from-40 ℃ to 0 to 5 ℃, then subjected to secondary heat exchange with normal-temperature water medium in the tube type heat exchanger to raise the temperature to 10 to 20 ℃, and then the condensate is sent to a purification process to remove trichlorosilane and silicon tetrachloride, so that the monomethyl trichlorosilane is obtained.
7. The method for preparing high-purity silicon carbide by chemical vapor deposition according to claim 1, wherein in the bubbling leaching process of the step (4), the leaching solution is chlorosilane liquid, and the chlorosilane liquid can be trichlorosilane or silicon tetrachloride.
8. The method for preparing high-purity silicon carbide by chemical vapor deposition according to claim 1, wherein in the step (5), the non-absorbed gases in the tail gas after bubbling and leaching are mainly hydrogen, alkane, chlorosilane and hydrogen chloride, and the remaining components except the hydrogen are adsorbed by an activated carbon adsorption column to obtain high-purity hydrogen.
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