Method for reducing content of carbon element in electronic-grade polycrystalline silicon in reduction process

Abstract

The invention belongs to the technical field of electronic-grade polycrystalline silicon production, and particularly relates to a method for reducing the content of carbon in electronic-grade polycrystalline silicon in a reduction process, and the method comprises the steps of preparation of nano porous palladium, preparation of a catalyst, purification of trichlorosilane and preparation of polycrystalline silicon. By preparing the catalyst with good activity and high reaction efficiency, maximum-limit conversion and removal of methyl dichlorosilane in trichlorosilane are realized, so that the carbon content in polycrystalline silicon is reduced, and the removal rate is greater than 98.5%; moreover, by controlling the raw material ratio, the reaction temperature, the reaction pressure and other conditions, the prepared electronic-grade polycrystalline silicon is low in carbon element content, and the high requirement of the semiconductor industry for the quality of the electronic-grade polycrystalline silicon is met.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic-grade polysilicon production, and in particular relates to a method for reducing the carbon content in electronic-grade polysilicon during a reduction process. Background Art

[0002] Polysilicon is an electronic material that uses industrial silicon as raw material and reaches a certain purity after a series of physical and chemical reactions. It is the core raw material for manufacturing silicon polished wafers, solar cells and semiconductors, and is the most basic material for the information industry and new energy industry. The purity of polysilicon determines the subsequent application areas. The solar-grade polysilicon used in the photovoltaic industry generally has a purity between 6N and 9N. The purity of electronic-grade polysilicon used in the production of semiconductors is required to reach 11N, and the process difficulty is far greater than that of solar-grade polysilicon.

[0003] High-purity polysilicon has the characteristics of high technical barriers, difficult processes, and high levels of danger. The current mainstream process is a modified version of the "Siemens method" invented by Siemens of Germany. This method uses trichlorosilane as a raw material. In a reduction furnace, trichlorosilane is reduced by hydrogen and vapor deposited on the silicon core to form polysilicon. The main factors affecting the purity of the modified Siemens method product include the purity of trichlorosilane and hydrogen. Among them, methyldichlorosilane in trichlorosilane has a boiling point close to that of trichlorosilane, and it is difficult to completely remove it by distillation and other means. It will enter the reduction furnace together with trichlorosilane and react in a hydrogen atmosphere to form silicon carbide. Silicon carbide will be deposited on the surface of silicon, thus affecting the quality of polysilicon.

[0004] On December 20, 2022, the State Intellectual Property Office disclosed an invention patent with the publication number "CN115490236A" and the name "A method and system for preparing trichlorosilane for electronic-grade polysilicon production". It discloses a method for preparing trichlorosilane for electronic-grade polysilicon production, using refined trichlorosilane in solar-grade polysilicon production as raw material, removing methyldichlorosilane through a decarbonization tower, and then removing heavy components through a support tower to obtain refined trichlorosilane with a metal impurity content not higher than 0.5ppbw, B and P impurities not higher than 0.05ppbw, and a total carbon content not higher than 0.1ppm.

[0005] As one of the main impurities in semiconductor materials, carbon seriously affects the electrical properties of products. Under certain conditions, carbon will become the nucleation center of oxygen atoms, promoting the precipitation of oxygen, thereby causing polysilicon lattice dislocation and forming deep-level carrier recombination centers, which ultimately shortens the service life of downstream products. Therefore, reducing the carbon content in polysilicon is one of the key factors in improving the quality of electronic-grade polysilicon, and one of the key points of reducing the carbon content in polysilicon is to reduce the content of methyldichlorosilane in trichlorosilane.

[0006] In order to solve the above problems, the present invention proposes a method for reducing the carbon content in electronic-grade polysilicon during a reduction process, so as to achieve the purpose of reducing the carbon content in electronic-grade polysilicon. Summary of the invention

[0007] In order to solve the problems existing in the prior art, the present invention provides a method for reducing the carbon content in electronic-grade polysilicon in a reduction process, so as to achieve the purpose of reducing the carbon content in electronic-grade polysilicon, which is specifically as follows: 1. First, study the effect of reaction temperature on the yield and carbon content of electronic-grade polysilicon. Determine the system pressure and raw material ratio, calculate the polysilicon yield and carbon content at reaction temperatures between 700℃ and 1300℃ and compare them, obtain the temperature at which the polysilicon yield is the highest and the carbon content is the lowest, and determine the specific values ​​at the corresponding temperature.

[0008] 2. Combined with the specific reaction temperature for the highest polysilicon yield and the lowest carbon content, the system pressure is controlled between 0.1MPa and 0.9MPa to compare the polysilicon yield and carbon content at the corresponding temperature, and the optimal system pressure for the highest polysilicon yield and the lowest carbon content within a given range is obtained.

[0009] 3. Combine the specific reaction temperature and system pressure with the highest polysilicon yield and the lowest carbon content to control H 2 The proportion is between 1 and 50 times that of trichlorosilane gas. By comparing the polysilicon output and carbon content, the optimal raw material ratio of polysilicon output and carbon content under given conditions is obtained.

[0010] 4. Prepare a catalyst with good activity and fast reaction to achieve the maximum conversion and removal of methyldichlorosilane in trichlorosilane, thereby reducing the carbon content in polysilicon.

[0011] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for reducing the carbon content in electronic grade polysilicon in a reduction process comprises the following steps: S1. Preparation of Nanoporous Palladium The PdAl alloy strip was placed in a NaOH solution and reacted for 24 h to remove Al. After the reaction, it was washed with deionized water and anhydrous ethanol in sequence, dried and crushed to obtain nanoporous Pd with an average pore size of 7 to 9 nm.

[0012] 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.

[0013] Preferably, the concentration of the NaOH solution is 0.9-1.4 mol / L.

[0014] The reaction equation of S1 is: 2Al+2NaOH+2H 2 O=2NaAlO 2 +3H 2 ↑.

[0015] S2. Preparation of Catalyst Nanoporous Pd was added to the prepared KMnO 4 The hydrothermal synthesis reaction in the solution generates MnO 2 The nanoporous Pd was uniformly loaded, and after the reaction, it was washed with deionized water and anhydrous ethanol in turn, and dried to obtain MnO 2 / porous Pd composite catalyst.

[0016] Preferably, the KMnO 4 In solution, KMnO 4 The amount of the crude drug is 1-10 mg, the amount of deionized water is 260-320 ml, and the amount of concentrated sulfuric acid is 48-55 μl.

[0017] Preferably, the nanoporous Pd and KMnO 4 KMnO in solution 4 The mass ratio is 1:0.5~1.

[0018] Preferably, the temperature of the hydrothermal synthesis is 120-180° C., and the time is 1-4 hours.

[0019] Preferably, the MnO 2 MnO / porous Pd composite catalyst 2 The mass share is 10.5-16%.

[0020] The reaction equation of S2 is: MnO 4 - +4H + =MnO 2 +2H 2 O.

[0021] S3. Purification of trichlorosilane Trichlorosilane and chlorine source containing methyldichlorosilane are fed into the reactor, and MnO 2 / porous Pd composite catalyst, catalytic reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point, and then methyltrichlorosilane is removed by distillation to separate trichlorosilane to obtain purified trichlorosilane.

[0022] Preferably, the chlorine source is carbon tetrachloride; and the molar ratio of the methyldichlorosilane to the chlorine source is 1:2.6-3.2.

[0023] Preferably, the MnO2 The added amount of the porous Pd composite catalyst is 0.7-1.4% of methyldichlorosilane.

[0024] Preferably, the catalytic reaction temperature is 110-130° C. and the time is 30-60 min.

[0025] Preferably, the content of methyldichlorosilane in the purified trichlorosilane is less than 0.5 ppb, and the removal rate is greater than 98.5%.

[0026] S4. Preparation of polysilicon The purified trichlorosilane is converted into gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas is introduced into the silicon rods for reaction while heating the silicon rods, so that silicon is deposited on the surface of the silicon rods to obtain electronic grade polysilicon.

[0027] Preferably, the mixed gas comprises hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane.

[0028] Preferably, in the mixed gas, the volume ratio of hydrogen gas to trichlorosilane gas containing trace amounts of methyldichlorosilane is 1 to 50:1.

[0029] Preferably, the heating is to increase the temperature of the reduction furnace to between 700°C and 1300°C and maintain the gas phase temperature on the surface of the silicon rods at 700°C to 1300°C.

[0030] Preferably, the reaction pressure is 0.1 MPa to 0.9 MPa.

[0031] Due to the adoption of the above technical solution, the technical effects achieved by the present invention are: 1. The content of methyldichlorosilane in the purified trichlorosilane prepared by the present invention is less than 0.5 ppb, and the removal rate is greater than 98.5%, while the content of methyldichlorosilane in trichlorosilane in the prior art is mostly above 1 ppb. In addition, the process of the present invention has a fast reaction time, simple operation and high conversion efficiency.

[0032] 2. The present invention controls the raw materials, reaction temperature, pressure and other conditions to prepare electronic-grade polysilicon with low carbon content, thus meeting the semiconductor industry's high requirements for the quality of electronic-grade polysilicon. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with specific embodiments.

[0034] Example 1: S1. Preparation of Nanoporous Palladium The PdAl alloy strip was placed in a NaOH solution and reacted for 24 h to remove Al. After the reaction, it was washed with deionized water and anhydrous ethanol in sequence, dried and crushed to obtain nanoporous Pd with an average pore size of 8 nm.

[0035] 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.

[0036] The concentration of the NaOH solution is 1.1 mol / L.

[0037] The reaction equation of S1 is: 2Al+2NaOH+2H 2 O=2NaAlO 2 +3H 2 ↑.

[0038] S2. Preparation of Catalyst Nanoporous Pd was added to the prepared KMnO 4 The hydrothermal synthesis reaction in the solution generates MnO 2 The nanoporous Pd was uniformly loaded, and after the reaction, it was washed with deionized water and anhydrous ethanol in turn, and dried to obtain MnO 2 / porous Pd composite catalyst.

[0039] The KMnO 4 In solution, KMnO 4 8 mg, deionized water is 300 ml, and concentrated sulfuric acid is 50 μl.

[0040] The nanoporous Pd and KMnO 4 KMnO in solution 4 The mass ratio is 1:0.8.

[0041] The temperature of the hydrothermal synthesis is 150° C. and the time is 2 h.

[0042] The MnO 2 MnO / porous Pd composite catalyst 2 The quality accounts for 12.4%.

[0043] The reaction equation of S2 is: MnO 4 - +4H + =MnO 2 +2H 2 O.

[0044] S3. Purification of trichlorosilane Trichlorosilane and chlorine source containing methyldichlorosilane are fed into the reactor, and MnO 2 / porous Pd composite catalyst, catalytic reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point, and then methyltrichlorosilane is removed by distillation to separate trichlorosilane to obtain purified trichlorosilane.

[0045] The chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:3.

[0046] The MnO 2 The addition amount of the porous Pd composite catalyst is 1.15% of methyldichlorosilane.

[0047] The temperature of the catalytic reaction is 120° C. and the time is 40 minutes.

[0048] The content of methyldichlorosilane in the purified trichlorosilane is 0.32 ppb, and the removal rate is 99.4%.

[0049] S4. Preparation of polysilicon The purified trichlorosilane is converted into gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas is introduced into the silicon rods for reaction while heating the silicon rods, so that silicon is deposited on the surface of the silicon rods to obtain electronic grade polysilicon.

[0050] The mixed gas includes hydrogen gas and trichlorosilane gas containing a trace amount of methyldichlorosilane.

[0051] In the mixed gas, the volume ratio of hydrogen gas to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1.

[0052] The heating is to increase the temperature of the reduction furnace to 1000° C. and maintain the gas phase temperature on the surface of the silicon rod at 1000° C.

[0053] The reaction pressure is 0.1 MPa.

[0054] Example 2: S1. Preparation of Nanoporous Palladium The PdAl alloy strip was placed in a NaOH solution and reacted for 24 h to remove Al. After the reaction, it was washed with deionized water and anhydrous ethanol in sequence, dried and crushed to obtain nanoporous Pd with an average pore size of 7 nm.

[0055] 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.

[0056] The concentration of the NaOH solution is 0.9 mol / L.

[0057] The reaction equation of S1 is: 2Al+2NaOH+2H 2 O=2NaAlO 2 +3H 2 ↑.

[0058] S2. Preparation of Catalyst Nanoporous Pd was added to the prepared KMnO 4The hydrothermal synthesis reaction in the solution generates MnO 2 The nanoporous Pd was uniformly loaded, and after the reaction, it was washed with deionized water and anhydrous ethanol in turn, and dried to obtain MnO 2 / porous Pd composite catalyst.

[0059] The KMnO 4 In solution, KMnO 4 1 mg, deionized water is 260 ml, and concentrated sulfuric acid is 48 μl.

[0060] The nanoporous Pd and KMnO 4 KMnO in solution 4 The mass ratio is 1:0.5.

[0061] The temperature of the hydrothermal synthesis is 120° C. and the time is 4 hours.

[0062] The MnO 2 MnO / porous Pd composite catalyst 2 The quality accounts for 10.5%.

[0063] The reaction equation of S2 is: MnO 4 - +4H + =MnO 2 +2H 2 O.

[0064] S3. Purification of trichlorosilane Trichlorosilane and chlorine source containing methyldichlorosilane are fed into the reactor, and MnO 2 / porous Pd composite catalyst, catalytic reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point, and then methyltrichlorosilane is removed by distillation to separate trichlorosilane to obtain purified trichlorosilane.

[0065] The chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:2.6.

[0066] The MnO 2 The added amount of the porous Pd composite catalyst is 0.7% of methyldichlorosilane.

[0067] The temperature of the catalytic reaction is 110° C. and the time is 30 minutes.

[0068] The content of methyldichlorosilane in the purified trichlorosilane is 0.48 ppb, and the removal rate is 98.6%.

[0069] S4. Preparation of polysilicon The purified trichlorosilane is converted into gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas is introduced into the silicon rods for reaction while heating the silicon rods, so that silicon is deposited on the surface of the silicon rods to obtain electronic grade polysilicon.

[0070] The mixed gas includes hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane; In the mixed gas, the volume ratio of hydrogen gas to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1.

[0071] The heating is to increase the temperature of the reduction furnace to 1000° C. and maintain the gas phase temperature on the surface of the silicon rod at 1000° C.

[0072] The reaction pressure is 0.1 MPa.

[0073] Example 3: S1. Preparation of Nanoporous Palladium The PdAl alloy strip was placed in a NaOH solution and reacted for 24 h to remove Al. After the reaction, it was washed with deionized water and anhydrous ethanol in sequence, dried and crushed to obtain nanoporous Pd with an average pore size of 9 nm.

[0074] 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.

[0075] The concentration of the NaOH solution is 1.4 mol / L.

[0076] The reaction equation of S1 is: 2Al+2NaOH+2H 2 O=2NaAlO 2 +3H 2 ↑.

[0077] S2. Preparation of Catalyst Nanoporous Pd was added to the prepared KMnO 4 The hydrothermal synthesis reaction in the solution generates MnO 2 The nanoporous Pd was uniformly loaded, and after the reaction, it was washed with deionized water and anhydrous ethanol in turn, and dried to obtain MnO 2 / porous Pd composite catalyst.

[0078] The KMnO 4 In solution, KMnO 4 10 mg, deionized water is 320 ml, and concentrated sulfuric acid is 55 μl.

[0079] The nanoporous Pd and KMnO 4 KMnO in solution 4 The mass ratio is 1:1.

[0080] The temperature of the hydrothermal synthesis is 180° C. and the time is 1 h.

[0081] The MnO 2 MnO / porous Pd composite catalyst 2 The quality accounts for 16%.

[0082] The reaction equation of S2 is: MnO 4 - +4H + =MnO 2 +2H 2 O.

[0083] S3. Purification of trichlorosilane Trichlorosilane and chlorine source containing methyldichlorosilane are fed into the reactor, and MnO 2 / porous Pd composite catalyst, catalytic reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point, and then methyltrichlorosilane is removed by distillation to separate trichlorosilane to obtain purified trichlorosilane.

[0084] The chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:3.2.

[0085] The MnO 2 The added amount of the porous Pd composite catalyst is 1.4% of methyldichlorosilane.

[0086] The temperature of the catalytic reaction is 130° C. and the time is 60 minutes.

[0087] The content of methyldichlorosilane in the purified trichlorosilane is 0.43 ppb, and the removal rate is 98.9%.

[0088] S4. Preparation of polysilicon The purified trichlorosilane is converted into gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane. The mixed gas is introduced into the silicon rods for reaction while heating the silicon rods, so that silicon is deposited on the surface of the silicon rods to obtain electronic grade polysilicon.

[0089] The mixed gas includes hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane; In the mixed gas, the volume ratio of hydrogen gas to trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1.

[0090] The heating is to increase the temperature of the reduction furnace to 1000° C. and maintain the gas phase temperature on the surface of the silicon rod at 1000° C.

[0091] The reaction pressure is 0.1 MPa.

[0092] Example 4: This example is different from Example 1 in that the heating in S4 is to increase the temperature of the reduction furnace to 700°C and maintain the gas phase temperature of the silicon rod surface at 700°C.

[0093] Example 5: This example is different from Example 1 in that the heating in S4 is to increase 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.

[0094] Example 6: This example is different from Example 1 in that the heating in S4 is to increase 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.

[0095] Embodiment 7: This embodiment differs from Embodiment 1 in that the heating in S4 is to increase 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.

[0096] Example 8: This example is different from Example 1 in that the reaction pressure in S4 is 0.3 MPa.

[0097] Example 9: This example is different from Example 1 in that the reaction pressure in S4 is 0.6 MPa.

[0098] Example 10: This example is different from Example 1 in that the reaction pressure in S4 is 0.9 MPa.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] The yield of polysilicon and the yield of carbon in polysilicon in Examples 1-12 were determined, and the proportion of silicon carbide in the total solid phase products (expressed as η) was determined to measure the content of carbon in polysilicon. The effects of the content of methyldichlorosilane in purified trichlorosilane, the ratio of mixed gas, temperature, and the pressure of the reaction system on polysilicon were studied. See Table 1-4 for details.

[0104] Table 1 Test 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 Table 2 Test 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 Table 3 Test 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 Table 4 Test items Si (mol) SiC (mol) η Embodiment 11 2.03E-01 9.74E-10 4.79E-09 Example 12 2.68E-01 7.25E-10 2.71E-09 Embodiment 13 3.37E-01 4.41E-10 1.31E-09 Embodiment 14 3.97E-01 1.57E-10 3.95E-10 It can be seen from Table 1 that the lower the content of methyldichlorosilane in the purified trichlorosilane, the lower the carbon content in the prepared polysilicon.

[0105] As can be seen from Table 2, when the volume ratio of hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1 and the pressure is 0.1 MPa, the carbon content in polysilicon gradually decreases with increasing reaction temperature. At 950°C, the carbon content in polysilicon is the lowest, which is 4.27E-09, and then begins to increase; while the yield of polysilicon gradually increases with increasing reaction temperature, reaching a maximum value of 2.15E-01 at 1000°C, and then begins to decrease.

[0106] It can be seen from Table 3 that when the volume ratio of hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane is 3:1 and the temperature is 1000°C, the carbon content in polysilicon gradually decreases with the increase of system pressure. The greater the system pressure, the less the carbon content in polysilicon. At 0.9MPa, the carbon content reaches a minimum of 8.88E-10; while the yield of polysilicon decreases with the increase of system pressure, reaching a maximum of 2.15E-01 at a system pressure of 0.1MPa.

[0107] It can be seen from Table 4 that when the pressure is 0.1MPa and the reaction temperature is 1000℃, the carbon content in polysilicon decreases with the increase of hydrogen flow rate. When the volume ratio of hydrogen to trichlorosilane gas containing trace methyldichlorosilane is 50:1, the carbon content in polysilicon is at least 3.95E-10; and the yield of polysilicon increases with the increase of H 2 and reaches a maximum value of 3.97E-01 when the volume ratio of hydrogen to trichlorosilane gas containing trace amounts of methyldichlorosilane is 50:1.

[0108] Unless otherwise specified, the percentages described in the present invention are all mass percentages, the ratios described are all mass ratios; and the raw materials described are all commercially available.

[0109] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for reducing the carbon content in electronic grade polysilicon in a reduction process, characterized in that: The method comprises the preparation of nanoporous palladium, the preparation of a catalyst, the purification of trichlorosilane and the preparation of polycrystalline silicon.

2. A method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, characterized in that: The nanoporous palladium is prepared by placing a PdAl alloy strip in a NaOH solution for a sufficient reaction for 24 hours to remove Al, washing it with deionized water and anhydrous ethanol in sequence after the reaction, drying it, and crushing it to obtain nanoporous Pd with an average pore size of 7 to 9 nm; The concentration of the NaOH solution is 0.9-1.4 mol / L.

3. A method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, characterized in that: The catalyst is prepared by adding nanoporous Pd to a prepared KMnO4 solution for a hydrothermal synthesis reaction, wherein the generated MnO2 is uniformly loaded on the nanoporous Pd, and after the reaction is completed, the nanoporous Pd is washed with deionized water and anhydrous ethanol in sequence, and the MnO2 / porous Pd composite catalyst is obtained after drying.

4. A method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 3, characterized in that: In the KMnO4 solution, KMnO4 is 1-10 mg, deionized water is 260-320 ml, and concentrated sulfuric acid is 48-55 μl.

5. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 3, characterized in that: The mass ratio of the nanoporous Pd to KMnO4 in the KMnO4 solution is 1:0.5-1; The hydrothermal synthesis temperature is 120-180°C and the time is 1-4h; The mass proportion of MnO2 in the MnO2 / porous Pd composite catalyst is 10.5-16%.

6. A method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, characterized in that: The purification of trichlorosilane is as follows: trichlorosilane containing methyldichlorosilane and a chlorine source are fed into a reaction kettle, a MnO2 / porous Pd composite catalyst is added, and a catalytic reaction is carried out under nitrogen conditions to convert methyldichlorosilane into methyltrichlorosilane with a higher boiling point, and then the methyltrichlorosilane is removed by distillation, and trichlorosilane is separated to obtain purified trichlorosilane.

7. A method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 6, characterized in that: The chlorine source is carbon tetrachloride; the molar ratio of methyldichlorosilane to the chlorine source is 1:2.6-3.2; The amount of the MnO2 / porous Pd composite catalyst added is 0.7-1.4% of methyldichlorosilane; The catalytic reaction temperature is 110-130°C and the reaction time is 30-60 minutes; The content of methyldichlorosilane in the purified trichlorosilane is lower than 0.5 ppb, and the removal rate is greater than 98.5%.

8. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 1, characterized in that: The preparation of the polysilicon comprises the following steps: converting purified trichlorosilane into gas phase to obtain trichlorosilane gas containing trace amounts of methyldichlorosilane; heating silicon rods while introducing a mixed gas for reaction to deposit silicon on the surface of the silicon rods to obtain electronic grade polysilicon.

9. A method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 8, characterized in that: The mixed gas includes hydrogen and trichlorosilane gas containing trace amounts of methyldichlorosilane; In the mixed gas, the volume ratio of hydrogen gas to trichlorosilane gas containing trace amounts of methyldichlorosilane is 1 to 50:

1.

10. The method for reducing the carbon content in electronic grade polysilicon in a reduction process according to claim 8, characterized in that: The heating is to increase the temperature of the reduction furnace to between 700°C and 1300°C, and maintain the gas phase temperature on the surface of the silicon rod at 700°C to 1300°C; The reaction pressure is 0.1 MPa to 0.9 MPa.