Primary Distillation Boron Reduction in Polysilicon Production
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing polycrystalline silicon struggle to effectively separate and remove boron compounds, which have low boiling points and are difficult to distinguish from trichlorosilane using commercial distillation processes, resulting in high boron impurities in the final product.
Innovation Solution
A fluidized-bed reactor is used to react metallurgical grade silicon with hydrogen chloride, followed by a distillation process where trichlorosilane and other compounds are condensed and distilled, with the liquid feed entering below a liquid level in the distillation unit to separate boron compounds, allowing for their removal and purification of trichlorosilane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If commercial distillation processes are used to separate trichlorosilane from boron compounds, then the distillation process is simple and commercially available, but the separation effectiveness is poor because boron compounds have low boiling points close to or lower than TCS
Solution Approach 1:
The patent changes the physical state parameter of the feed by cooling it to sub-zero temperatures (e.g., -30°C to -100°C) before distillation. This parameter change causes low-boiling-point boron compounds to remain in liquid form while TCS vaporizes, achieving effective separation that conventional distillation cannot accomplish.
Solution Approach 2:
The patent uses a composite approach by combining temperature-controlled feed introduction with distillation. The cooled liquid feed creates a temperature gradient within the distillation column, establishing a composite thermal environment that enables selective vaporization and separation of components based on their volatility differences.
2Manufacturing precision
If the liquid feed is introduced above the liquid level in the distillation unit, then the distillation process is simple, but boron compounds cannot be effectively removed
Solution Approach 1:
The patent introduces the feed in a different spatial dimension by injecting it below the liquid level rather than above. This dimensional change in feed introduction allows the cold liquid feed to create a temperature gradient throughout the liquid column, enabling effective separation of boron compounds through controlled vaporization.
3Manufacturing precision
If ether group addition method is used to remove boron compounds, then boron removal is achieved, but additional ether group recovery and refining steps are necessary
Solution Approach 1:
The patent extracts boron compounds from the mixture by introducing cooled liquid TCS below the liquid level in the distillation column. The temperature difference causes boron compounds to remain in the liquid phase while TCS vaporizes, effectively extracting and separating the impurities without requiring additional chemical treatment or recovery steps.
4Manufacturing precision
If silica bed is used to purify vapor phase TCS, then boron compounds are removed, but a fixed bed of silica is required which needs maintenance
Solution Approach 1:
The patent replaces the mechanical adsorption system (silica bed) with a thermal separation system. By introducing cooled liquid feed below the liquid level, the system uses temperature-driven vaporization to separate TCS from boron compounds, eliminating the need for mechanical adsorbent beds and their associated maintenance requirements.
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
This method significantly reduces boron content in the polycrystalline silicon production, achieving a 13.9 times decrease in boron ppm, leading to higher purity and efficiency in the distillation process.
Implementation Method 1
reacting metallurgical grade silicon with hydrogen chloride to produce a reacted gas including TCS and other compounds
Implementation Method 2
a condenser for condensing TCS and other compounds produced in the fluidized-bed reactor into a liquid
Implementation Method 3
a distillation unit for purifying the TCS wherein the liquid TCS and other compounds enters the distillation unit below a liquid level in the distillation unit
Data Source
AI summary
The present invention relates to an apparatus and a method for producing polycrystalline silicon having a reduced amount of boron compound impurities. Especially, the boron compounds are removed from the process for producing polycrystalline silicon, while the trichlorosilane is purified by distillation. The invention feeds condensed liquid trichlorosilane into a primary distillation tower below the liquid level inside the primary distillation tower thereby scrubbing the boron impurities upon contact inside the primary distillation tower. There result is trichlorosilane leaving the primary distillation tower with total amount of boron at least 10 times less.