# US 11,440,803 B2 · Process for preparing polycrystalline silicon > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,440,803 B2 - Document ID: US11440803B2 - Status: Granted - Kind: B2 - Application number: 16/469,628 - Filed: 2016-12-14 - Published: 2020-04-30 - Granted: 2022-09-13 - Earliest claimed: 2016-12-14 - Assignees: Wacker Chemie AG - Applicants: Wacker Chemie AG - Inventors: Harald Hertlein; Dirk Weckesser - Web page: https://patentgrep.com/patent/US11440803B2 ## CPC - C01B 33/03: by decomposition of silicon halides or halosilanes or reduction thereof with hydrogen as the only reducing agent - C01B 33/02: Silicon (forming single crystals or homogeneous polycrystalline material with defined structure C30B) - C01B: NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; {METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C} ## Abstract The invention relates to a method for producing polycrystalline silicon granulate in a fluidized bed reactor. The method comprises a fluidization of silicon seed particles by means of a fluidizing gas in a fluidized bed, which is heated by a heating device, wherein elemental silicon is deposited by pyrolysis on the silicon seed particles by the addition of a reaction gas containing hydrogen and silane and/or halosilane to form the polycrystalline silicon granulate. In a continuous process, waste gas is discharged from the fluidized bed reactor and hydrogen recovered from said waste to gas is again supplied to the fluidized bed reactor as a circulating gas. The circulating gas has a nitrogen content of less than 1000 ppmv. The invention further relates to polycrystalline silicon granulate having a nitrogen content of less than 2 ppba. ## Claims ### Claim 1 A method for producing a polycrystalline silicon granulate in a fluidized bed reactor, comprising: fluidizing silicon seed particles using a fluidizing gas in a fluidized bed reactor having a reactor wall, which is heated a heating apparatus; adding a reaction gas comprising hydrogen, and a silane and/or a halosilane; and depositing elemental silicon, by pyrolysis, onto the silicon seed particles to form the polycrystalline silicon granulate; and discharging an offgas from a recycle gas system for workup of offgases of the fluidized bed reactor and directing hydrogen recovered from the offgas back to the fluidized bed reactor as a recycle gas, wherein the recycle gas contains nitrogen, and when the nitrogen content exceeds a predetermined threshold value between 0.01 and 1000 ppmv, the reactor is shut down, the reactor continues to operate with external hydrogen and no recycle hydrogen or a lesser amount of recycle hydrogen, or the temperature of the fluidized bed and/or the reactor wall is/are increased until the nitrogen concentration falls below the predetermined threshold value. ### Claim 2 (depends on 1) The method of claim 1, wherein the nitrogen content of the recycle gas is less than 500 ppmv. ### Claim 3 (depends on 1) The method of claim 1, wherein the nitrogen content of the recycle gas is less than 100 ppmv. ### Claim 4 (depends on 1) The method of claim 1, wherein the nitrogen content of the recycle gas is less than 0.5 ppmv. ### Claim 5 (depends on 1) The method of claim 1, wherein the deposition of elemental silicon is carried out at a deposition temperature between 1000° C. and 1300° C. ### Claim 6 (depends on 1) The method of claim 1, wherein the deposition of elemental silicon is carried out at a deposition temperature between 1080° C. and 1250° C. ### Claim 7 (depends on 1) The method of claim 1, wherein the deposition of elemental silicon is carried out at a deposition temperature between 1100° C. and 1200° C. ### Claim 8 (depends on 1) The method of claim 1, wherein the nitrogen content of the recycle gas is measured by a gas chromatograph. ### Claim 9 (depends on 1) The method of claim 1, wherein when the predetermined nitrogen threshold value of nitrogen is exceeded the fluidized bed reactor is shut down. ### Claim 10 (depends on 1) The method of claim 1, wherein when the predetermined threshold value of nitrogen is exceeded, flow of recycle gas is interrupted and the method is operated with external hydrogen until the nitrogen concentration reaches or is below threshold value of nitrogen. ### Claim 11 (depends on 1) The method of claim 1, wherein upon exceeding the predetermined threshold value of nitrogen, the temperature of the fluidized bed and/or of the reactor wall is increased until the nitrogen concentration reaches or is below the predetermined threshold value of nitrogen. ### Claim 12 (depends on 1) The method of claim 1, wherein the recycle gas is admixed with less than 90% of external hydrogen. ### Claim 13 (depends on 1) The method of claim 1, wherein the recycle gas is admixed with less than 40% of external hydrogen. ### Claim 14 (depends on 1) The method of claim 1, wherein the recycle gas is admixed with less than 10% of external hydrogen. ### Claim 15 (depends on 1) The method of claim 1, wherein the halosilane is a chlorosilane. ### Claim 16 (depends on 1) The method of claim 1, wherein the halosilane is a trichlorosilane. ### Claim 17 (depends on 1) The method of claim 1, wherein before commencement of the method a pressurization with hydrogen followed by a depressurization is carried out inside the fluidized bed reactor, wherein a maximum pressure during pressurization is in the range between 3.1 and 15 bar, and a minimum pressure during depressurization is in the range between 1.1 and 3 bar. ### Claim 18 (depends on 17) The method of claim 17, wherein the pressurization and the depressurization each have a duration between 1 and 60 min. ### Claim 19 (depends on 18) The method of claim 18, wherein the pressurization is carried out with a hydrogen volume flow per reactor volume VR between 10 and 7000 m3/hVR. ### Claim 20 (depends on 1) A polycrystalline silicon granulate comprising an Si3N4 content of less than 1 ppba, prepared by the method of claim 1. ### Claim 21 (depends on 19) The polycrystalline silicon granulate of claim 19, comprising a surface roughness Ra≥400 nm.