Zinc Chloride Secondary Refining for Industrial Silicon Purification
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Solution Overview
Problem
Conventional methods for removing phosphorus and boron impurities from industrial silicon melts are costly and cumbersome, requiring multiple metal elements and high-energy processes, which increases operational expenses and introduces additional impurities.
Innovation Solution
A secondary refining method using zinc chloride vaporized with a carrier gas at high temperatures to react with phosphorus and boron impurities, allowing low-melting compounds to volatilize and high-melting compounds to be segregated and removed, without introducing new impurities, utilizing a simple and low-energy process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional directional solidification is used to remove impurities, then metal elements can be removed from silicon, but phosphorus and boron impurities cannot be effectively removed due to large segregation coefficients
Solution Approach 1:
The patent changes the fundamental parameter of impurity removal mechanism from physical segregation (directional solidification) to chemical reaction. By introducing zinc chloride as a chemical reagent that reacts with phosphorus and boron impurities to form volatile compounds, the method overcomes the limitation of large segregation coefficients for these impurities, enabling effective removal through chemical transformation rather than physical separation.
Solution Approach 2:
The patent introduces zinc chloride as an intermediary substance that mediates the impurity removal process. Zinc chloride reacts with phosphorus and boron impurities to form intermediate volatile compounds (such as zinc phosphide and zinc boride), which then escape from the silicon melt. This intermediary mechanism enables selective removal of impurities that cannot be removed by direct physical separation methods.
2Manufacturing precision
If multiple metal elements (aluminum, hafnium, calcium, magnesium) are added to remove impurities sequentially, then phosphorus and boron can be removed, but the process becomes cumbersome and costly
Solution Approach 1:
The patent merges the removal of multiple impurities (phosphorus and boron) into a single operational step by using zinc chloride as a universal reagent. Instead of sequentially adding different metal elements for different impurities, the method combines multiple impurity removal functions into one process, significantly simplifying the operational complexity while maintaining effective impurity removal.
Solution Approach 2:
The patent makes zinc chloride a universal impurity removal agent that can handle multiple impurity types (phosphorus and boron) simultaneously. This multi-functional reagent replaces the need for multiple specialized metal elements, reducing both the number of operations and the overall process complexity while achieving comprehensive impurity removal.
3Manufacturing precision
If high-purity aluminum and high-purity hafnium are added to remove boron impurities, then boron content decreases, but the cost significantly increases due to expensive metals
Solution Approach 1:
The patent replaces expensive long-lasting metal elements (aluminum, hafnium) with a cheaper, more versatile chemical compound (zinc chloride) that can be easily added and decomposed. Zinc chloride serves as a disposable reagent that effectively removes boron impurities through chemical reaction, eliminating the need for costly metal additions while maintaining impurity removal effectiveness.
Solution Approach 2:
The patent changes the chemical composition approach from using metal elements to using zinc chloride compound. This parameter change in the reagent type enables cost-effective impurity removal through chemical reactions rather than relying on expensive metal additions, significantly reducing production costs while achieving the same boron removal effect.
4Manufacturing precision
If high-purity aluminum, calcium, and magnesium are added to remove phosphorus impurities, then phosphorus content decreases, but the process complexity and cost increase
Solution Approach 1:
The patent makes zinc chloride a universal reagent that can remove both phosphorus and boron impurities through chemical reactions. This multi-functional approach eliminates the need to add different metal elements for different impurities, reducing the number of operational steps and simplifying the overall process while achieving effective phosphorus removal.
Solution Approach 2:
The patent combines the removal of phosphorus and boron impurities into a single process step using zinc chloride, rather than requiring separate steps for each impurity. This merging of functions reduces process complexity and eliminates the need to manage multiple metal element additions, making the overall manufacturing process simpler and more efficient.
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
Effectively reduces phosphorus and boron content in industrial silicon to meet solar-grade purity standards with reduced energy consumption and operational costs, using widely sourced and low-cost zinc chloride, ensuring efficient impurity removal without introducing new contaminants.
Implementation Method 1
vaporizing and adding zinc chloride to a silicon melt by means of the carrier gas
Implementation Method 2
reaction of chloride and zinc ions generated by decomposition of the zinc chloride with the phosphorus and boron impurities
Implementation Method 3
allowing low-melting compounds yielded by a reaction... to volatilize and escape
Implementation Method 4
introducing a carrier gas to a ladle, vaporizing and adding zinc chloride to a silicon melt by means of the carrier gas
Implementation Method 5
controlling a temperature of the silicon melt greater than or equal to 1,700° C.
Implementation Method 6
decomposition of the zinc chloride with the phosphorus and boron impurities
Data Source
AI summary
A method for removing phosphorus and boron impurities in an industrial silicon melt by secondary refining is provided. According to the present disclosure, inorganic zinc chloride is adopted as an impurity removal medium and is quickly decomposed into zinc and chloride ions at high temperatures; the phosphorus and boron impurities can react with the zinc and chloride ions to yield low-melting and high-melting compounds during contact with a silicon melt, the low-melting compounds volatilize and escape from the industrial silicon melt at the high temperature of the secondary refining. The high-melting compounds are segregated at the grain boundary along with silicon solidification and removed by crushing and pickling, or sink to the very bottom of the silicon melt and are removed by cutting off a deposition layer at a bottom of a silicon ingot after the silicon melt is solidified.