Halosilane Purification via Membrane and Condensation
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Solution Overview
Problem
Current high purity silicon production processes face challenges in efficiently removing impurities from metallurgical grade silicon, particularly in recycle streams, leading to impurity buildup and decreased purity over time, due to lack of systematic identification of impurity sinks and inefficient recycling of carrier chemicals.
Innovation Solution
A process involving the separation of halosilanes into low and high boiling streams, followed by membrane separation to remove methane and phosphine, and additional filtration steps to remove aluminum trichloride, with a focus on clearly identifying sinks for impurities and recycling halogen-based systems to minimize waste and maintain high purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If carrier chemicals are recycled to reduce waste, then waste loss is minimized, but impurity buildup occurs in recycle streams leading to decreased purity over time
Solution Approach 1:
The patent extracts impurities from the recycle streams by introducing dedicated removal steps at strategic locations. Impurity sinks are established to selectively remove carbon and phosphorus from the carrier chemical recycle loops, allowing the carrier chemicals to be recycled while preventing impurity accumulation that would otherwise degrade silicon purity over time.
Solution Approach 2:
The patent applies local quality by placing impurity removal capabilities at specific locations within the process where impurities are most effectively removed. Different sink locations are optimized for different impurity types - for example, removing carbon at locations where it forms condensable compounds while removing phosphorus where it can be effectively separated, thereby maintaining overall system purity while enabling carrier chemical recycling.
2Manufacturing precision
If multiple purification steps are added to maintain high purity, then silicon purity is improved, but process complexity increases
Solution Approach 1:
The patent applies preliminary action by removing impurities from carrier chemical recycle streams before they can accumulate and contaminate the final silicon product. By establishing impurity sinks upstream in the process, the need for complex downstream purification steps is reduced, as impurities are prevented from building up in the first place.
Solution Approach 2:
The patent discards impurities at strategic points in the process while recovering and recycling the carrier chemicals. Impurity sinks are designed to selectively remove carbon and phosphorus compounds from the recycle streams, allowing the valuable carrier chemicals to be recovered and reused without the impurities that would otherwise require complex purification to remove.
3Manufacturing precision
If impurities are removed from recycle streams, then silicon purity is maintained, but additional process steps are required
Solution Approach 1:
The patent applies universality by designing impurity sinks that can handle multiple types of impurities (carbon, phosphorus, and other metal contaminants) through a single integrated removal mechanism. The carrier chemical recycle system itself serves multiple functions: transporting silicon, enabling chemical reactions, and providing a medium through which impurities can be selectively removed at designated sink locations.
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 approach effectively reduces impurity concentrations in recycle streams, minimizes waste, and maintains high purity silicon production by systematically removing impurities at optimal locations, thereby reducing the cost and complexity of downstream purification processes.
Implementation Method 1
passing some or all the gases through a membrane system to remove greater than 50% of any methane present and/or any phosphine present
Implementation Method 2
cooling a reactor effluent stream containing primarily halosilanes, condensing more than 50% of the halosilanes
Data Source
Figure 1~2
Figure 2a~3
Figure 4a~4b
AI summary
A set of three low cost processes for removing boron, phosphorus, carbon and other metal and nonmetal impurities during the process of converting metallurgical grade silicon to electronic grade silicon. One process removes boron by using one or more high temperature solids removal devices to remove solid titanium diboride from a halosilane reactor effluent stream where the high temperature is preferably greater than 200 C, more preferably greater than 300 C and most preferably greater than 400 C . A second process removes carbon as methane and phosphorus as phosphine by means of a membrane separator which processes all or part of a hydrogen recycle stream to recover hydrogen while rejecting methane and phosphine. A third process separates a high boiling halosilane stream into a large low impurity stream and one or more small high impurity streams some of which can be sent for halogen recovery.