A method for reducing the carbon content in electronic-grade polysilicon using a reduction process

Abstract

This invention belongs to the field of electronic-grade polycrystalline silicon production technology. Specifically, it is a method for reducing the carbon content in electronic-grade polycrystalline silicon through a reduction process. The method includes the preparation of nanoporous palladium, catalyst preparation, purification of trichlorosilane, and preparation of polycrystalline silicon. This invention achieves maximum conversion and removal of methyldichlorosilane from trichlorosilane by preparing a catalyst with high activity and high reaction efficiency, thereby reducing the carbon content in polycrystalline silicon, with a removal rate greater than 98.5%. Furthermore, by controlling the raw material ratio, reaction temperature, pressure, and other conditions, this invention produces electronic-grade polycrystalline silicon with low carbon content, meeting the high quality requirements of the semiconductor industry.

Description

Technical Field

[0001] This invention belongs to the field of electronic-grade polycrystalline silicon production technology, specifically relating to a method for reducing the carbon content in electronic-grade polycrystalline silicon during a reduction process. Background Technology

[0002] Polycrystalline silicon is an electronic material made from industrial silicon through a series of physicochemical reactions to achieve a certain purity. It is a core raw material for manufacturing silicon wafers, solar cells, and semiconductors, and is the most fundamental material for the information and new energy industries. The purity of polycrystalline silicon determines its subsequent application areas. The solar-grade polycrystalline silicon used in the photovoltaic industry generally has a purity between 6N and 9N. Electronic-grade polycrystalline silicon used in semiconductor production requires a purity of 11N, and its manufacturing process is far more complex than that of solar-grade polycrystalline silicon.

[0003] High-purity polycrystalline silicon is characterized by high technical barriers, complex processes, and high safety levels. Currently, the mainstream process is a modified version of the "Siemens process" invented by Siemens AG of Germany. This method uses trichlorosilane as a raw material, which is reduced by hydrogen in a reduction furnace, and the vapor phase is deposited on the silicon core to form polycrystalline silicon. The main factors affecting the purity of the modified Siemens process product include the purity of trichlorosilane and hydrogen. Methyldichlorosilane in trichlorosilane, due to its close boiling point to trichlorosilane, is difficult to completely remove by distillation and enters the reduction furnace along with the trichlorosilane. There, it reacts in a hydrogen atmosphere to form silicon carbide, which deposits on the silicon surface, thus affecting the quality of the polycrystalline silicon.

[0004] On December 20, 2022, the State Intellectual Property Office published an invention patent with publication number "CN115490236A" entitled "A method and system for preparing trichlorosilane for the production of electronic-grade polycrystalline silicon". The patent discloses a method for preparing trichlorosilane for the production of electronic-grade polycrystalline silicon. The method uses refined trichlorosilane from the production of solar-grade polycrystalline silicon as raw material. The raw material is methyldichlorosilane removed by a decarbonization tower and heavy components removed by a weighting tower to obtain refined trichlorosilane with a metal impurity content of no more than 0.5 ppbw, B and P impurities of no more than 0.05 ppbw, and total carbon content of no more than 0.1 ppm.

[0005] Carbon, as one of the main impurities in semiconductor materials, significantly affects the electrical performance of products. Under certain conditions, carbon can become a nucleation center for oxygen atoms, promoting oxygen precipitation, which leads to lattice dislocations in polycrystalline silicon and the formation of deep-level carrier recombination centers, ultimately shortening the lifespan of downstream products. Therefore, reducing the carbon content in polycrystalline silicon is one of the key factors in improving the quality of electronic-grade polycrystalline silicon, and one of the key aspects of reducing the carbon content in polycrystalline silicon is reducing the content of methyldichlorosilane in trichlorosilane.

[0006] To address the aforementioned problems, this invention proposes a method for reducing the carbon content in electronic-grade polysilicon during the reduction process, thereby achieving the goal of reducing the carbon content in electronic-grade polysilicon. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for reducing the carbon content in electronic-grade polysilicon during a reduction process, thereby achieving the goal of reducing the carbon content in electronic-grade polysilicon, as detailed below:

[0008] 1. First, the effect of reaction temperature on the yield and carbon content of electronic-grade polysilicon was studied. The system pressure and raw material ratio were determined, and the polysilicon yield and carbon content at reaction temperatures between 700℃ and 1300℃ were calculated and compared to find the temperatures at which the polysilicon yield was highest and the carbon content was lowest, and the specific values ​​at the corresponding temperatures were determined.

[0009] 2. By combining the specific reaction temperatures that yield the highest polysilicon production and the lowest carbon content, and controlling the system pressure between 0.1 MPa and 0.9 MPa, the polysilicon production and carbon content at the corresponding temperatures are compared to determine the optimal system pressure within a given range that yields the highest polysilicon production and the lowest carbon content.

[0010] 3. By combining the specific reaction temperature and system pressure that result in the highest polysilicon yield and the lowest carbon content, and controlling the H2 ratio to be between 1 and 50 times that of trichlorosilane gas, the optimal raw material ratio for polysilicon yield and carbon content under given conditions is determined by comparing the polysilicon yield and carbon content.

[0011] 4. Prepare catalysts with high activity and fast reaction to achieve maximum conversion and removal of methyldichlorosilane in trichlorosilane, thereby reducing the carbon content in polycrystalline silicon.

[0012] To solve the above technical problems, the present invention adopts the following technical solution:

[0013] A method for reducing the carbon content in electronic-grade polysilicon during a reduction process includes the following steps:

[0014] S1, Preparation of nanoporous palladium

[0015] The PdAl alloy strip was placed in NaOH solution and reacted for 24 h to remove Al. After the reaction was completed, it was washed with deionized water and anhydrous ethanol in sequence, dried and pulverized to obtain nanoporous Pd with an average pore size of 7-9 nm.

[0016] Preferably, in the PdAl alloy strip, Pd accounts for 10% of the total mass of the PdAl alloy strip, and Al accounts for 90% of the total mass of the PdAl alloy strip.

[0017] Preferably, the concentration of the NaOH solution is 0.9–1.4 mol / L.

[0018] The reaction equation for S1 is: 2Al + 2NaOH + 2H2O = 2NaAlO2 + 3H2↑.

[0019] S2, Catalyst Preparation

[0020] Nanoporous Pd was added to a prepared KMnO4 solution for hydrothermal synthesis. The generated MnO2 was uniformly loaded on the nanoporous Pd. After the reaction was completed, the catalyst was washed with deionized water and anhydrous ethanol in sequence and dried to obtain the MnO2 / porous Pd composite catalyst.

[0021] Preferably, in the KMnO4 solution, the amount of KMnO4 is 1-10 mg, the amount of deionized water is 260-320 ml, and the amount of concentrated sulfuric acid is 48-55 μl.

[0022] Preferably, the mass ratio of the nanoporous Pd to the KMnO4 in the KMnO4 solution is 1:0.5 to 1.

[0023] Preferably, the hydrothermal synthesis is carried out at a temperature of 120–180°C for 1–4 hours.

[0024] Preferably, the mass percentage of MnO2 in the MnO2 / porous Pd composite catalyst is 10.5-16%.

[0025] The reaction equation for S2 is: MnO4 - +4H + =MnO2+2H2O.

[0026] Purification of S3 and trichlorosilane

[0027] Trichlorosilane containing methyldichlorosilane and a chlorine source are fed into a reactor, and a MnO2 / porous Pd composite catalyst is added. The reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point. The methyltrichlorosilane is then removed by distillation, and the trichlorosilane is separated to obtain purified trichlorosilane.

[0028] Preferably, the chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:2.6 to 3.2.

[0029] Preferably, the amount of the MnO2 / porous Pd composite catalyst added is 0.7 to 1.4% of methyldichlorosilane.

[0030] Preferably, the temperature of the catalytic reaction is 110–130°C and the time is 30–60 min.

[0031] Preferably, the content of methyldichlorosilane in the purified trichlorosilane is less than 0.5 ppb, and the removal rate is greater than 98.5%.

[0032] S4. Preparation of polycrystalline silicon

[0033] The purified trichlorosilane was converted into a gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas was introduced into the silicon rod while the silicon rod was heated to react and allow silicon to be deposited on the surface of the silicon rod, thus obtaining electronic-grade polycrystalline silicon.

[0034] Preferably, the mixed gas comprises hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane.

[0035] Preferably, in the mixed gas, the volume ratio of hydrogen to trichlorosilane gas containing trace amounts of methyldichlorosilane is 1 to 50:1.

[0036] Preferably, the heating involves raising the temperature of the reduction furnace to between 700°C and 1300°C, while maintaining the vapor temperature on the surface of the silicon rod at between 700°C and 1300°C.

[0037] Preferably, the reaction pressure is 0.1 MPa to 0.9 MPa.

[0038] By adopting the above technical solution, the technical effect achieved by this invention is as follows:

[0039] 1. The purified trichlorosilane prepared by this invention has a methyldichlorosilane content of less than 0.5 ppb and a removal rate of more than 98.5%, while the methyldichlorosilane content in trichlorosilane in the prior art is mostly above 1 ppb. Furthermore, the process of this invention has a fast reaction time, simple operation, and high conversion efficiency.

[0040] 2. By controlling the raw materials, reaction temperature, pressure and other conditions, the present invention prepares electronic-grade polycrystalline silicon with low carbon content, which meets the high quality requirements of the semiconductor industry for electronic-grade polycrystalline silicon. Detailed Implementation

[0041] The present invention will be further illustrated below with reference to specific embodiments.

[0042] Example 1: Preparation of S1 and nanoporous palladium

[0043] The PdAl alloy strip was placed in NaOH solution and reacted for 24 h to remove Al. After the reaction was completed, it was washed with deionized water and anhydrous ethanol in sequence, dried and pulverized to obtain nanoporous Pd with an average pore size of 8 nm.

[0044] In the PdAl alloy strip, Pd accounts for 10% of the total mass of the PdAl alloy strip, and Al accounts for 90% of the total mass of the PdAl alloy strip.

[0045] The concentration of the NaOH solution is 1.1 mol / L.

[0046] The reaction equation for S1 is: 2Al + 2NaOH + 2H2O = 2NaAlO2 + 3H2↑.

[0047] S2, Catalyst Preparation

[0048] Nanoporous Pd was added to a prepared KMnO4 solution for hydrothermal synthesis. The generated MnO2 was uniformly loaded on the nanoporous Pd. After the reaction was completed, the catalyst was washed with deionized water and anhydrous ethanol in sequence and dried to obtain the MnO2 / porous Pd composite catalyst.

[0049] The KMnO4 solution contained 8 mg of KMnO4, 300 ml of deionized water, and 50 μl of concentrated sulfuric acid.

[0050] The mass ratio of the nanoporous Pd to the KMnO4 in the KMnO4 solution is 1:0.8.

[0051] The hydrothermal synthesis was carried out at a temperature of 150°C for 2 hours.

[0052] The mass percentage of MnO2 in the MnO2 / porous Pd composite catalyst is 12.4%.

[0053] The reaction equation for S2 is: MnO4 - +4H + =MnO2+2H2O.

[0054] Purification of S3 and trichlorosilane

[0055] Trichlorosilane containing methyldichlorosilane and a chlorine source are fed into a reactor, and a MnO2 / porous Pd composite catalyst is added. The reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point. The methyltrichlorosilane is then removed by distillation, and the trichlorosilane is separated to obtain purified trichlorosilane.

[0056] The chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:3.

[0057] The amount of the MnO2 / porous Pd composite catalyst added is 1.15% of methyldichlorosilane.

[0058] The catalytic reaction was carried out at a temperature of 120°C for 40 minutes.

[0059] The purified trichlorosilane contained 0.32 ppb of methyldichlorosilane, with a removal rate of 99.4%.

[0060] S4. Preparation of polycrystalline silicon

[0061] The purified trichlorosilane was converted into a gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas was introduced into the silicon rod while the silicon rod was heated to react and allow silicon to be deposited on the surface of the silicon rod, thus obtaining electronic-grade polycrystalline silicon.

[0062] The mixed gas includes hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane.

[0063] In the mixed gas, the volume ratio of hydrogen to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1.

[0064] The heating process involves raising the temperature of the reduction furnace to 1000°C and maintaining the vapor temperature on the surface of the silicon rod at 1000°C.

[0065] The reaction was carried out at a pressure of 0.1 MPa.

[0066] Example 2: Preparation of S1 and nanoporous palladium

[0067] The PdAl alloy strip was placed in NaOH solution and reacted for 24 h to remove Al. After the reaction was completed, it was washed with deionized water and anhydrous ethanol in sequence, dried and pulverized to obtain nanoporous Pd with an average pore size of 7 nm.

[0068] In the PdAl alloy strip, Pd accounts for 10% of the total mass of the PdAl alloy strip, and Al accounts for 90% of the total mass of the PdAl alloy strip.

[0069] The concentration of the NaOH solution is 0.9 mol / L.

[0070] The reaction equation for S1 is: 2Al + 2NaOH + 2H2O = 2NaAlO2 + 3H2↑.

[0071] S2, Catalyst Preparation

[0072] Nanoporous Pd was added to a prepared KMnO4 solution for hydrothermal synthesis. The generated MnO2 was uniformly loaded on the nanoporous Pd. After the reaction was completed, the catalyst was washed with deionized water and anhydrous ethanol in sequence and dried to obtain the MnO2 / porous Pd composite catalyst.

[0073] The KMnO4 solution contained 1 mg of KMnO4, 260 ml of deionized water, and 48 μl of concentrated sulfuric acid.

[0074] The mass ratio of the nanoporous Pd to the KMnO4 in the KMnO4 solution is 1:0.5.

[0075] The hydrothermal synthesis was carried out at a temperature of 120°C for 4 hours.

[0076] The mass percentage of MnO2 in the MnO2 / porous Pd composite catalyst is 10.5%.

[0077] The reaction equation for S2 is: MnO4 - +4H + =MnO2+2H2O.

[0078] Purification of S3 and trichlorosilane

[0079] Trichlorosilane containing methyldichlorosilane and a chlorine source are fed into a reactor, and a MnO2 / porous Pd composite catalyst is added. The reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point. The methyltrichlorosilane is then removed by distillation, and the trichlorosilane is separated to obtain purified trichlorosilane.

[0080] The chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:2.6.

[0081] The amount of the MnO2 / porous Pd composite catalyst added is 0.7% of methyldichlorosilane.

[0082] The catalytic reaction was carried out at a temperature of 110°C for 30 minutes.

[0083] The purified trichlorosilane contained 0.48 ppb of methyldichlorosilane, with a removal rate of 98.6%.

[0084] S4. Preparation of polycrystalline silicon

[0085] The purified trichlorosilane was converted into a gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas was introduced into the silicon rod while the silicon rod was heated to react and allow silicon to be deposited on the surface of the silicon rod, thus obtaining electronic-grade polycrystalline silicon.

[0086] The mixed gas includes hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane;

[0087] In the mixed gas, the volume ratio of hydrogen to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1.

[0088] The heating process involves raising the temperature of the reduction furnace to 1000°C and maintaining the vapor temperature on the surface of the silicon rod at 1000°C.

[0089] The reaction was carried out at a pressure of 0.1 MPa.

[0090] Example 3: Preparation of S1 and nanoporous palladium

[0091] The PdAl alloy strip was placed in NaOH solution and reacted for 24 h to remove Al. After the reaction was completed, it was washed with deionized water and anhydrous ethanol in sequence, dried and pulverized to obtain nanoporous Pd with an average pore size of 9 nm.

[0092] In the PdAl alloy strip, Pd accounts for 10% of the total mass of the PdAl alloy strip, and Al accounts for 90% of the total mass of the PdAl alloy strip.

[0093] The concentration of the NaOH solution is 1.4 mol / L.

[0094] The reaction equation for S1 is: 2Al + 2NaOH + 2H2O = 2NaAlO2 + 3H2↑.

[0095] S2, Catalyst Preparation

[0096] Nanoporous Pd was added to a prepared KMnO4 solution for hydrothermal synthesis. The generated MnO2 was uniformly loaded on the nanoporous Pd. After the reaction was completed, the catalyst was washed with deionized water and anhydrous ethanol in sequence and dried to obtain the MnO2 / porous Pd composite catalyst.

[0097] The KMnO4 solution contained 10 mg of KMnO4, 320 ml of deionized water, and 55 μl of concentrated sulfuric acid.

[0098] The mass ratio of the nanoporous Pd to the KMnO4 in the KMnO4 solution is 1:1.

[0099] The hydrothermal synthesis was performed at a temperature of 180°C for 1 hour.

[0100] The mass percentage of MnO2 in the MnO2 / porous Pd composite catalyst is 16%.

[0101] The reaction equation for S2 is: MnO4 - +4H + =MnO2+2H2O.

[0102] Purification of S3 and trichlorosilane

[0103] Trichlorosilane containing methyldichlorosilane and a chlorine source are fed into a reactor, and a MnO2 / porous Pd composite catalyst is added. The reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point. The methyltrichlorosilane is then removed by distillation, and the trichlorosilane is separated to obtain purified trichlorosilane.

[0104] The chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:3.2.

[0105] The amount of MnO2 / porous Pd composite catalyst added is 1.4% of methyldichlorosilane.

[0106] The catalytic reaction was carried out at a temperature of 130°C for 60 minutes.

[0107] The purified trichlorosilane contained 0.43 ppb of methyldichlorosilane, with a removal rate of 98.9%.

[0108] S4. Preparation of polycrystalline silicon

[0109] The purified trichlorosilane was converted into a gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas was introduced into the silicon rod while the silicon rod was heated to react and allow silicon to be deposited on the surface of the silicon rod, thus obtaining electronic-grade polycrystalline silicon.

[0110] The mixed gas includes hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane;

[0111] In the mixed gas, the volume ratio of hydrogen to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1.

[0112] The heating process involves raising the temperature of the reduction furnace to 1000°C and maintaining the vapor temperature on the surface of the silicon rod at 1000°C.

[0113] The reaction was carried out at a pressure of 0.1 MPa.

[0114] Example 4: The difference between this example and Example 1 is that in S4, the heating is performed by raising the temperature of the reduction furnace to 700°C and maintaining the gas phase temperature on the surface of the silicon rod at 700°C.

[0115] Example 5: The difference between this example and Example 1 is that the heating in S4 is to raise the temperature of the reduction furnace to 950°C and maintain the gas phase temperature on the surface of the silicon rod at 950°C.

[0116] Example 6: The difference between this example and Example 1 is that the heating in S4 is to raise the temperature of the reduction furnace to 1150°C and maintain the gas phase temperature on the surface of the silicon rod at 1150°C.

[0117] Example 7: The difference between this example and Example 1 is that the heating in S4 is to raise the temperature of the reduction furnace to 1300°C and maintain the gas phase temperature on the surface of the silicon rod at 1300°C.

[0118] Example 8: The difference between this example and Example 1 is that the reaction pressure in S4 is 0.3 MPa.

[0119] Example 9: The difference between this example and Example 1 is that the reaction pressure in S4 is 0.6 MPa.

[0120] Example 10: The difference between this example and Example 1 is that the reaction pressure in S4 is 0.9 MPa.

[0121] Example 11: The difference between this example and Example 1 is that in the mixed gas of S4, the volume ratio of hydrogen gas and trichlorosilane gas containing trace amounts of methyldichlorosilane is 1:1.

[0122] Example 12: The difference between this example and Example 1 is that in the mixed gas of S4, the volume ratio of hydrogen gas and trichlorosilane gas containing trace amounts of methyldichlorosilane is 10:1.

[0123] Example 13: The difference between this example and Example 1 is that in the mixed gas of S4, the volume ratio of hydrogen gas and trichlorosilane gas containing trace amounts of methyldichlorosilane is 20:1.

[0124] Example 14: The difference between this example and Example 1 is that in the mixed gas of S4, the volume ratio of hydrogen gas and trichlorosilane gas containing trace amounts of methyldichlorosilane is 50:1.

[0125] The yield of polycrystalline silicon and the yield of carbon in polycrystalline silicon were determined in Examples 1-12. The proportion of silicon carbide in the total solid product (denoted by η) was measured to measure the carbon content in polycrystalline silicon. The effects of the content of methyldichlorosilane in purified trichlorosilane, the ratio of mixed gases, temperature, and reaction system pressure on polycrystalline silicon were studied. See Tables 1-4 for details.

[0126] Table 1

[0127] Testing items Si (mol) SiC (mol) η Example 1 2.15E-01 9.21E-10 4.29E-09 Example 2 1.75E-01 9.55E-10 5.40E-09 Example 3 1.97E-01 9.31E-10 4.73E-09

[0128] Table 2

[0129] Testing items Si (mol) SiC (mol) η Example 4 1.85E-01 8.47E-10 4.57E-09 Example 5 2.14E-01 9.12E-10 4.27E-09 Example 6 1.82E-01 9.41E-10 5.17E-09 Example 7 9.32E-02 9.55E-10 1.02E-08

[0130] Table 3

[0131] Testing items Si (mol) SiC (mol) η Example 8 1.95E-01 7.43E-10 3.82E-09 Example 9 1.78E-01 4.55E-10 2.55E-09 Example 10 1.68E-01 1.49E-10 8.88E-10

[0132] Table 4

[0133] Testing items Si (mol) SiC (mol) η Example 11 2.03E-01 9.74E-10 4.79E-09 Example 12 2.68E-01 7.25E-10 2.71E-09 Example 13 3.37E-01 4.41E-10 1.31E-09 Example 14 3.97E-01 1.57E-10 3.95E-10

[0134] As can be seen from Table 1, the lower the content of methyldichlorosilane in the purified trichlorosilane, the lower the carbon content in the prepared polycrystalline silicon.

[0135] As shown in Table 2, when the volume ratio of hydrogen to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1 and the pressure is 0.1 MPa, the carbon content in polycrystalline silicon gradually decreases with increasing reaction temperature, reaching its lowest value of 4.27E-09 at 950℃, after which it begins to increase. Meanwhile, the yield of polycrystalline silicon gradually increases with increasing reaction temperature, reaching a maximum value of 2.15E-01 at 1000℃, after which it begins to decrease.

[0136] As shown in Table 3, when the volume ratio of hydrogen to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1 and the temperature is 1000℃, the carbon content in polycrystalline silicon gradually decreases with increasing system pressure. The higher the system pressure, the lower the carbon content in polycrystalline silicon, reaching a minimum of 8.88E-10 at 0.9 MPa. Meanwhile, the yield of polycrystalline silicon decreases with increasing system pressure, reaching a maximum of 2.15E-01 at a system pressure of 0.1 MPa.

[0137] As shown in Table 4, when the pressure is 0.1 MPa and the reaction temperature is 1000℃, the carbon content in polycrystalline silicon decreases with the increase of hydrogen flow rate. The carbon content in polycrystalline silicon is the lowest at a volume ratio of 3.95E-10 when the volume ratio of hydrogen to trichlorosilane containing trace amounts of methyldichlorosilane is 50:1. The yield of polycrystalline silicon increases with the increase of H2, reaching a maximum of 3.97E-01 when the volume ratio of hydrogen to trichlorosilane containing trace amounts of methyldichlorosilane is 50:1.

[0138] Unless otherwise specified, all percentages mentioned in this invention are mass percentages, all ratios are mass ratios, and all raw materials are commercially available.

[0139] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of reducing the carbon content in electronic grade polysilicon in a reduction process, characterized in that, The method comprises preparation of nano-porous palladium, preparation of catalyst, purification of trichlorosilane and preparation of polysilicon; The preparation of the nano-porous palladium is that the PdAl alloy strip is put into a NaOH solution for reaction for 24 hours to remove Al, and then the nano-porous Pd is obtained by washing with deionized water and anhydrous ethanol and crushing after drying, with an average pore size of 7-9 nm; The concentration of the NaOH solution is 0.9-1.4 mol / L; The preparation of the catalyst is that the nano-porous Pd is put into a prepared KMnO4 solution for hydrothermal synthesis reaction, and the generated MnO2 is uniformly loaded on the nano-porous Pd, and then the MnO2 / porous Pd composite catalyst is obtained by washing with deionized water and anhydrous ethanol and drying after the reaction; The purification of the trichlorosilane is that the trichlorosilane containing methyl dichlorosilane and a chlorine source are fed into a reaction kettle, the MnO2 / porous Pd composite catalyst is added, and catalytic reaction is carried out under nitrogen to convert the methyl dichlorosilane into methyl trichlorosilane with a higher boiling point, and then the methyl trichlorosilane is removed by rectification, the trichlorosilane is separated, and the purified trichlorosilane is obtained; The preparation of the polysilicon is that the purified trichlorosilane is converted into a gas phase to obtain trichlorosilane gas containing trace methyl dichlorosilane, and the mixed gas is introduced while heating the silicon rod to make the silicon deposit on the surface of the silicon rod to obtain electronic-grade polysilicon.

2. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, wherein, In the KMnO4 solution, the KMnO4 is 1-10 mg, the deionized water is 260-320 ml, and the concentrated sulfuric acid is 48-55 μl.

3. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, wherein the carbon content in the electronic grade polysilicon is reduced to 1 x 10"9 or less. The mass ratio of the nano-porous Pd to the KMnO4 in the KMnO4 solution is 1:0.5-1; The temperature of the hydrothermal synthesis is 120-180 ℃, and the time is 1-4 h; The mass ratio of the MnO2 in the MnO2 / porous Pd composite catalyst is 10.5-16%.

4. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, wherein the carbon content in the electronic grade polysilicon is reduced to 1 x 10"9 or less. The chlorine source is carbon tetrachloride; the molar ratio of the methyl dichlorosilane to the chlorine source is 1:2.6-3.2; The addition amount of the MnO2 / porous Pd composite catalyst is 0.7-1.4% of the methyl dichlorosilane; The temperature of the catalytic reaction is 110-130 ℃, and the time is 30-60 min; The content of the methyl dichlorosilane in the purified trichlorosilane is less than 0.5 ppb, and the removal rate is greater than 98.5%.

5. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, wherein the carbon content in the electronic grade polysilicon is reduced to 1 x 10"9 or less. The mixed gas comprises hydrogen and trichlorosilane gas containing trace methyl dichlorosilane; In the mixed gas, the volume ratio of the hydrogen to the trichlorosilane gas containing trace methyl dichlorosilane is 1-50:

1.

6. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, wherein the carbon content in the electronic grade polysilicon is reduced to 1 x 10"9 or less. The heating is that the temperature of the reduction furnace is increased to 700-1300 ℃, and the gas phase temperature on the surface of the silicon rod is maintained at 700-1300 ℃; The pressure of the reaction is 0.1-0.9 MPa.