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A method for removing boron and phosphorus impurities in silicon by molten salt electrolysis

A molten salt electrolysis and electrolyte technology, applied in the electrolysis process, electrolysis components, silicon and other directions, to achieve the effect of reducing the electrolysis temperature, reducing the electrolysis voltage, and low energy consumption.

Active Publication Date: 2015-09-02
XIAMEN UNIV
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0006] The purpose of the present invention is to provide a method for removing boron and phosphorus impurities in silicon by molten salt electrolysis with high selectivity and simple process in view of the limitations of existing metallurgical methods for removing impurity elements B and P in polysilicon

Method used

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  • A method for removing boron and phosphorus impurities in silicon by molten salt electrolysis

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Experimental program
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Embodiment 1

[0045] Using metal Si powder with a purity of 99% and metal Cu powder with a purity of 99.9% as raw materials, mix the two metal powders according to a molar ratio of 7:3, then heat to 1450°C and melt in a low vacuum with a vacuum degree of about 10Pa; After smelting for 2 hours, the melt was directly poured into a graphite mold and cooled to obtain a Si-Cu alloy.

[0046] The prepared Si-Cu alloy is used as the anode of the electrolytic cell, and solar-grade polysilicon (impurity content is less than 1ppm) is used as the cathode substrate; the electrolyte is CaCl 2 -NaCl-CaO-SiO 2 Molten salt system, CaCl 2 Purity: 99.5%, NaCl purity: 99.6%, CaO purity: 97%, SiO 2 Purity: 99.9%, molar ratio of each component: 80mol% CaCl 2 -10mol% NaCl-5mol%CaO-5mol%SiO2. Protected by high-purity argon gas during electrolysis, electrolysis temperature: 800°C, electrolysis time: 20h, electrolysis voltage: 0.8V; current density: 0.5A / cm 2 ; Deposit high-purity silicon on the cathode (SOG-S...

Embodiment 2

[0051] Using metal Si powder with a purity of 99.5%, 99.9% metal Cu powder and 99.9% metal Ni powder as raw materials, mix the two metal powders according to the molar ratio of 8:1:1, and then heat to 1400 ° C, low Vacuum smelting, the vacuum degree is about 10Pa; after smelting for 2 hours, the melt is directly poured into a graphite mold and cooled to obtain a Si-Cu-Ni alloy.

[0052] The prepared Si-Cu-Ni alloy is used as the anode of the electrolytic cell, and high-purity graphite is used as the cathode substrate; the electrolyte chloride-oxide molten salt system, CaCl 2 Purity: 99.5%, KCl purity: 99.6%, CaO purity: 97%, SiO 2 Purity: 99.9%, molar ratio of each component: 80mol% CaCl 2 -10mol% KCl-5mol% CaO-5mol% SiO 2 ;Argon protection during electrolysis, electrolysis temperature: 750°C, electrolysis time: 30h, electrolysis voltage: 1.0V; current density: 0.6A / cm 2 ; Deposit high-purity silicon on the cathode (high-purity graphite) during the electrolytic refining pro...

Embodiment 3

[0055] Using metal Si powder with a purity of 99.5% and metal Ni powder with a purity of 99.9% as raw materials, the two metal powders are mixed according to a molar ratio of 7:3, and then heated to 1200°C for low vacuum melting with a vacuum degree of about 10Pa; After smelting for 2 hours, the melt was directly poured into a graphite mold and cooled to obtain a Si-Ni alloy.

[0056] The prepared Si-Ni alloy is used as the anode of the electrolytic cell, and the high-purity metal Al is used as the cathode substrate; the electrolyte chloride-oxide molten salt system, CaCl 2 Purity: 99.5%, AlCl 3 Purity: 99.6%, CaO purity: 97%, Si purity: 99.9%, molar ratio of each component: 80mol% CaCl 2 -10mol% AlCl 3 -5mol% CaO-5mol% Si; argon protection during electrolysis, electrolysis temperature: 800°C, electrolysis time: 20h, electrolysis voltage: 1.2V; current density: 0.75A / cm 2 ; Deposit high-purity silicon at the cathode during the electrolytic refining process.

[0057] Crush ...

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Abstract

The invention relates to a polysilicon material purification method, and relates to a method for removing boron and phosphorus impurities in silicon through molten salt electrolysis. The method provided by the invention has high selectivity and simple process. The method comprises the steps of Si-M alloy anode preparation, electrolyte pretreatment, electrolytic tank assembly, and polysilicon purification by molten salt electrolysis. According to the invention, Si-M alloy is subjected to vacuum melting, such that a soluble anode is obtained. A composite chloride-oxide composite molten salt is adopted as a novel low-temperature electrolyte system. Metal, cemented carbide, solar-grade polysilicon, or high-purity graphite is adopted as a cathode. With the method provided by the invention, electrolysis temperature and electrolysis voltage are further reduced, such that highly efficient, stable, and low-power operation of the electrolysis process are ensured. With the method, high-selectivity purification of impurity elements B and P in polysilicon can be realized.

Description

technical field [0001] The invention relates to a method for purifying polycrystalline silicon materials, in particular to a method for removing boron and phosphorus in silicon materials by using molten salt electrolysis. Background technique [0002] Molten salt electrolysis is a new technology to prepare low-cost high-purity silicon. The current research mainly focuses on the following aspects (1) SiO 2 Direct molten salt electrolysis. SiO 2 When preparing solar-grade polysilicon by direct molten salt electrolysis of silicon source, the main components of the electrolyte are fluoride or chloride system, and SiO dissolved in the electrolyte 2 or silicates. SiO 2 Direct molten salt electrolysis has high temperature and high energy consumption, and it is difficult to obtain 6N solar grade polysilicon. (2) Preparation of solar-grade polysilicon by direct molten salt electrolysis of fluorosilicate. When using fluorosilicate as the silicon source to directly prepare solar...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C25B1/00C01B33/02
Inventor 罗学涛方明蔡靖李锦堂余德钦林彦旭卢成浩
Owner XIAMEN UNIV