Trichlorosilane Purification via Multistage Impurity Conversion
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Solution Overview
Problem
Conventional methods for purifying trichlorosilane face challenges in efficiently removing donor and acceptor impurities, such as phosphorus and boron, due to instability of adducts during distillation and equilibrium constraints, leading to re-contamination and reduced purity in polycrystalline silicon production.
Innovation Solution
A multistage system that converts impurities in trichlorosilane into high boiling point compounds using a distillation aid, followed by a purification step, comprising a series of impurity conversion sections with integrated reception, introduction, and transmission sections, and a distiller to separate high boiling point compounds and distillation aid, ensuring efficient removal and prevention of re-contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-stage impurity conversion method is used, then the process is simple, but the purification efficiency is insufficient and impurities remain in the final product
Solution Approach 1:
The impurity conversion process is divided into multiple stages (first impurity conversion step, second impurity conversion step, etc.), where each stage uses different distillation aids and operating conditions to convert different types of impurities into high boiling point compounds. This segmentation allows systematic removal of various impurities that cannot be effectively removed in a single stage.
Solution Approach 2:
Before the final distillation step, the impurities are preliminarily converted into high boiling point compounds through multiple conversion steps using different reagents (such as chlorine gas, oxygen, ozone). This preliminary conversion prepares the impurities for effective separation in the subsequent distillation process, ensuring they remain in the liquid phase while the trichlorosilane vaporizes.
2Manufacturing precision
If distillation is used to separate impurities from trichlorosilane, then separation is achieved, but impurities with boiling points close to trichlorosilane cannot be sufficiently removed
Solution Approach 1:
The method changes the physical and chemical parameters of the impurities by converting them into high boiling point compounds through chemical reactions with distillation aids (such as forming phosphorus oxychloride from phosphorus). This parameter change in boiling point creates sufficient separation between the impurities and trichlorosilane, enabling effective distillation separation.
Solution Approach 2:
Distillation aids (such as chlorine gas, oxygen, ozone) are introduced as intermediaries to facilitate the conversion of impurities into high boiling point compounds. These intermediaries enable the transformation that makes subsequent distillation separation effective, acting as a bridge between the original impurities and the separable high boiling point products.
3Manufacturing precision
If adsorption methods are used to remove impurities, then impurity removal is achieved, but the apparatus becomes complicated and waste disposal becomes troublesome
Solution Approach 1:
The patent replaces the mechanical adsorption system (requiring adsorption towers, adsorbent replacement procedures) with a chemical conversion system followed by distillation. The chemical conversion process transforms impurities into separable compounds, and the distillation process physically separates them, eliminating the need for complex adsorption equipment and simplifying waste disposal.
4Manufacturing precision
If organic substances are added as distillation aids to form adducts with impurities, then impurity conversion is achieved, but adduct instability causes re-contamination during distillation
Solution Approach 1:
Instead of forming unstable adducts, the method changes the chemical nature of impurities by converting them into high boiling point compounds with completely different physical properties. This parameter change ensures the converted impurities remain stable throughout the distillation process and do not dissociate or re-contaminate the purified trichlorosilane.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves high purity trichlorosilane with impurity concentrations below 2 ppta for donors and 20 ppta for acceptors, suppressing impurity mixing into polycrystalline silicon and minimizing distillation aid and trichlorosilane discharge, while requiring no special facilities for liquefaction.
Implementation Method 1
an impurity conversion section that converts an impurity comprised in the trichlorosilane into a high boiling point compound in the presence of a distillation aid
Implementation Method 2
a purification section that distills and purifies the trichlorosilane supplied from the impurity conversion section
Data Source
AI summary
A system for purifying trichlorosilane that can prevent re-contamination by the dissociation of an adduct occurring in association with the conversion of high boiling point compounds or the remaining of impurities due to an equilibrium constraint is provided. Trichlorosilane containing impurities serving as a donor or an acceptor in silicon crystals is supplied to a multistage impurity conversion step. These impurities in the trichlorosilane are converted into high boiling point compounds in the presence of a distillation aid. A plurality of impurity conversion step sections (101 to 10n) are connected in series, and any of the impurity conversion step sections comprises a reception section a for the trichlorosilane from the preceding stage section, an introduction section b for the distillation aid, a transmission section c for the trichlorosilane to the subsequent stage section, and a drain section d that discharges a remainder out of the impurity conversion step section.