Method for removing boron and phosphorus impurities in cold hydrogenation reaction product in polycrystalline silicon production

Abstract

The invention relates to the technical field of polycrystalline silicon production, and particularly discloses a method for removing boron and phosphorus impurities in a cold hydrogenation reaction product in polycrystalline silicon production, which comprises the following steps: S1, adding hexachlorodisiloxane into a rectifying tower feed of the cold hydrogenation reaction product, and rectifying the hexachlorodisiloxane and the cold hydrogenation reaction product together; s2, respectively collecting a tower top product and a tower bottom liquid phase mixture of the rectifying tower in the step S1; s3, feeding the tower bottom liquid phase mixture in the step S2 into a coarse separation tower, and separating and recovering hexachlorodisiloxane; s4, feeding hexachlorodisiloxane recovered in the step S3 into a rectifying tower of a cold hydrogenation reaction product, mixing the hexachlorodisiloxane with the cold hydrogenation reaction product, and feeding; by adding hexachlorodisiloxane during rectification of a cold hydrogenation reaction product, the effect of reducing the B / P content is obvious, hexachlorodisiloxane is a reaction by-product, the use cost is low, and hexachlorodisiloxane can be recycled and reused, so that the production cost can be greatly saved, and the purity of a polycrystalline silicon product is improved.

Description

Technical Field

[0001] The invention relates to the technical field of polysilicon production, and in particular to a method for removing boron and phosphorus impurities in a cold hydrogenation reaction product in polysilicon production. Background Art

[0002] Cold hydrogenation technology is often used in the production of polysilicon. The reaction is carried out under high pressure and low temperature conditions. Compared with other synthetic trichlorosilane (TCS), it has lower energy consumption and lower cost, so it is suitable for large-scale production of polysilicon. The cold hydrogenation process mainly uses silicon tetrachloride (STC), industrial silicon powder and hydrogen as reaction raw materials. Industrial silicon powder is often mixed with various metal and non-metal impurities, among which non-metal impurities are mainly impurity elements such as boron (B) and phosphorus (P). After the cold hydrogenation reaction, boron compounds such as BCl3 and PCl3 and PC Phosphorus compounds such as I5 are present in the reaction products. Such impurities have a boiling point close to that of trichlorosilane, silicon tetrachloride and other products, and are difficult to remove by distillation purification. The high content of B and P impurities in the reaction products leads to an increase in the content of B and P impurities in silicon rods produced by subsequent vapor deposition, and are enriched in the product silicon rods, affecting the quality of polysilicon products. Polysilicon has the characteristics of a semiconductor and is a very critical semiconductor material. However, the small amount of impurities therein has a very large effect on its conductivity. Therefore, the control of B and P impurities is extremely critical in the production of polysilicon. Summary of the invention

[0003] The object of the present invention is to provide a method for removing boron and phosphorus impurities in the cold hydrogenation reaction product in the production of polysilicon, so as to solve the problems existing in the prior art.

[0004] The present invention is implemented by the following technical scheme: a method for removing boron and phosphorus impurities in a cold hydrogenation reaction product in polysilicon production, comprising the following steps: S1: adding hexachlorodisiloxane to the feed of the distillation tower of the cold hydrogenation reaction product, and distilling the hexachlorodisiloxane and the cold hydrogenation reaction product together; S2: collecting the top product of the distillation tower and the liquid phase mixture at the bottom of the tower in step S1 respectively; S3: sending the liquid phase mixture at the bottom of the tower in step S2 to a coarse separation tower to separate and recover hexachlorodisiloxane; S4: sending the hexachlorodisiloxane recovered in step S3 to a distillation tower of the cold hydrogenation reaction product, mixing with the cold hydrogenation reaction product and then feeding.

[0005] Furthermore, in step S1, the volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:20-1:1000.

[0006] Furthermore, in step S2, the temperature of the product fraction at the top of the distillation tower is 30-60°C.

[0007] Furthermore, the volume ratio of the hexachlorodisiloxane recovered in step S4 to the cold hydrogenation reaction product is 1:20-1:1000.

[0008] Furthermore, in the step S3, the pressure inside the coarse powder tower for recovering hexachlorodisiloxane is 600-700 Kpa, and the tower temperature is 100-110°C.

[0009] The invention has the advantages that hexachlorodisiloxane is added to the cold hydrogenation reaction product and mixed, and the two products are fractionated together in a distillation tower, so that the B / P content is significantly reduced, and the hexachlorodisiloxane can be recycled at the bottom of the distillation tower. The hexachlorodisiloxane itself is a reaction by-product with low use cost and can be recycled and reused, which can greatly save production costs and improve the purity of polysilicon products. DETAILED DESCRIPTION

[0010] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0011] In the production process of polysilicon, a large number of by-products are generated. Most of the by-products are sent to the recovery process for separate extraction after distillation separation. Among them, the by-product hexachlorodisiloxane is a kind of by-product with a high boiling point. According to experimental research, hexachlorodisiloxane and the product of cold hydrogenation reaction are sent to the distillation tower for fractionation. The B and P impurities in the main product trichlorosilane and the recovered silicon tetrachloride are significantly reduced. The added hexachlorodisiloxane can be recovered in the liquid phase at the bottom of the distillation tower. The liquid phase at the bottom of the distillation tower is then sent to the recovery process for purification to obtain hexachlorodisiloxane. Therefore, hexachlorodisiloxane can be used as a de-impurity agent to remove the B and P impurities in the product of the cold hydrogenation reaction, thereby reducing the B and P impurities in the product. At the same time, hexachlorodisiloxane is easy to recover, purify and reuse.

[0012] The following describes the method for removing B and P impurities in the cold hydrogenation reaction product in polysilicon production provided by the present invention in conjunction with the embodiments: Embodiment 1: A method for removing boron and phosphorus impurities from a cold hydrogenation reaction product in polysilicon production, comprising the following steps: S1: adding hexachlorodisiloxane to the feed of the distillation tower of the cold hydrogenation reaction product, distilling the hexachlorodisiloxane and the cold hydrogenation reaction product together, the feed volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:20; S2: collecting the top product of the distillation tower and the liquid phase mixture at the bottom of the tower in step S1 respectively, the fraction collected at 30-34°C at the top of the tower is trichlorosilane, and the fraction collected at 57-60°C is silicon tetrachloride, and the product collected at the top of the tower is the product after impurity removal and purification; S3: sending the liquid phase mixture at the bottom of the tower in step S2 to a coarse fractionation tower to separate and recover hexachlorodisiloxane; the coarse powder tower pressure is 600 kPa, and the tower temperature is controlled at 100-110° C.; S4: sending the hexachlorodisiloxane recovered in step S3 to a distillation tower of the cold hydrogenation reaction product, utilizing the recovered hexachlorodisiloxane to remove impurities again, mixing with the cold hydrogenation reaction product and then feeding, wherein the volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:20.

[0013] The top product obtained in step S2 was sampled, and the contents of B and P impurities in the top product were detected by ICP-OES. Compared with the sample without adding hexachlorodisiloxane, the B element was reduced by 90.87% and the P element was reduced by 80.84%.

[0014] Embodiment 2: A method for removing boron and phosphorus impurities from a cold hydrogenation reaction product in polysilicon production, comprising the following steps: S1: adding hexachlorodisiloxane to the feed of the distillation tower of the cold hydrogenation reaction product, distilling the hexachlorodisiloxane and the cold hydrogenation reaction product together, and the feed volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:40.

[0015] S2: Collect the top product of the distillation tower and the liquid mixture at the bottom of the tower in step S1 respectively. The fraction collected at 30-34°C at the top of the tower is trichlorosilane, and the fraction collected at 57-60°C is silicon tetrachloride. The product collected at the top of the tower is the product after impurity removal and purification.

[0016] S3: sending the liquid phase mixture at the bottom of the tower in step S2 to a coarse fractionation tower to separate and recover hexachlorodisiloxane; the coarse powder tower pressure is 600 kPa, and the tower temperature is controlled at 100-110°C.

[0017] S4: sending the hexachlorodisiloxane recovered in step S3 to a distillation tower of the cold hydrogenation reaction product, utilizing the recovered hexachlorodisiloxane to remove impurities again, mixing with the cold hydrogenation reaction product and then feeding, wherein the volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:40.

[0018] The top product obtained in step S2 was sampled, and the contents of B and P impurities in the top product were detected by ICP-OES. Compared with the sample without adding hexachlorodisiloxane, the B element was reduced by 96% and the P element was reduced by 99%.

[0019] Embodiment 3: A method for removing boron and phosphorus impurities from a cold hydrogenation reaction product in polysilicon production, comprising the following steps: S1: adding hexachlorodisiloxane to the feed of the distillation tower of the cold hydrogenation reaction product, distilling the hexachlorodisiloxane and the cold hydrogenation reaction product together, and the feed volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:1000.

[0020] S2: Collect the top product of the distillation tower and the liquid mixture at the bottom of the tower in step S1 respectively. The fraction collected at 30-34°C at the top of the tower is trichlorosilane, and the fraction collected at 57-60°C is silicon tetrachloride. The product collected at the top of the tower is the product after impurity removal and purification.

[0021] S3: sending the liquid phase mixture at the bottom of the tower in step S2 to a coarse fractionation tower to separate and recover hexachlorodisiloxane; the coarse powder tower pressure is 700 kPa, and the tower temperature is controlled at 100-110°C.

[0022] S4: sending the hexachlorodisiloxane recovered in step S3 to a distillation tower of the cold hydrogenation reaction product, utilizing the recovered hexachlorodisiloxane to remove impurities again, mixing with the cold hydrogenation reaction product and then feeding, wherein the volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:1000.

[0023] The top product obtained in step S2 was sampled, and the contents of B and P impurities in the top product were detected by ICP-OES. Compared with the sample without adding hexachlorodisiloxane, the B element was reduced by 99.08% and the P element was reduced by 81.6%.

[0024] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing boron and phosphorus impurities from the cold hydrogenation reaction product in polysilicon production, characterized in that: The following steps are involved: S1: adding hexachlorodisiloxane to the feed of the distillation tower of the cold hydrogenation reaction product, and distilling the hexachlorodisiloxane and the cold hydrogenation reaction product together; S2: collecting the top product of the distillation tower and the liquid phase mixture at the bottom of the tower in step S1 respectively; S3: sending the liquid phase mixture at the bottom of the tower in step S2 to a coarse separation tower to separate and recover hexachlorodisiloxane; S4: sending the hexachlorodisiloxane recovered in step S3 to a distillation tower of the cold hydrogenation reaction product, mixing with the cold hydrogenation reaction product and then feeding.

2. A method for removing boron and phosphorus impurities from a cold hydrogenation reaction product in polysilicon production according to claim 1, characterized in that: In the step S1, the volume ratio of hexachlorodisiloxane to the cold hydrogenation reaction product is 1:20-1:1000.

3. The method for removing boron and phosphorus impurities in the cold hydrogenation reaction product in polysilicon production according to claim 1, characterized in that: The temperature of the product fraction at the top of the distillation tower in step S2 is 30-60°C.

4. The method for removing boron and phosphorus impurities in the cold hydrogenation reaction product in polysilicon production according to claim 1, characterized in that: The volume ratio of the hexachlorodisiloxane recovered in step S4 to the cold hydrogenation reaction product is 1:20-1:1000.

5. The method for removing boron and phosphorus impurities in the cold hydrogenation reaction product in polysilicon production according to claim 1, characterized in that: In the step S3, the pressure inside the coarse powder tower for recovering hexachlorodisiloxane is 600-700 KPa, and the tower temperature is 100-110°C.