Polycrystalline Silicon Rod Impurity Removal Process
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Solution Overview
Problem
Current methods for producing polycrystalline silicon masses for single-crystal silicon growth, such as the Siemens method, fail to adequately remove heavy metal impurities like chromium, iron, nickel, and copper from the bulk of the material, which contaminate the silicon melt and reduce the quality of CZ single-crystal silicon, especially in the multi pulling method.
Innovation Solution
A process involving the removal of at least 70 mm of the polycrystalline silicon portion from the electrode side end of the rod before crushing, followed by a silicon oxide coating using ozone water to reduce impurity concentrations to below 75 ppta, and using a polyethylene bag to minimize contamination during extraction and crushing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the Siemens method is used to produce polycrystalline silicon by vapor deposition, then polycrystalline silicon can be obtained, but heavy metal impurities (chromium, iron, nickel, copper) remain in the bulk material and contaminate the silicon melt
Solution Approach 1:
The patent applies preliminary action by removing the electrode-side end portion of the polycrystalline silicon rod before crushing. This preliminary removal eliminates the source of heavy metal impurities (chromium, iron, nickel, copper) that would otherwise be introduced during the crushing process, preventing contamination before it occurs in the first place.
Solution Approach 2:
The patent extracts and removes the contaminated portion of the polycrystalline silicon rod (the electrode-side end portion) that contains concentrated heavy metal impurities. By separating and discarding this contaminated section before crushing, the clean polycrystalline silicon masses are protected from impurity contamination.
2Ease of manufacture
If polycrystalline silicon masses with insufficient purity are used, then production cost is reduced, but impurities are taken into the CZ single-crystal silicon, inhibiting higher purity
Solution Approach 1:
The patent implements preliminary action by removing the electrode-side end portion containing heavy metal impurities before the crushing step. This prevents impurity contamination of the polycrystalline silicon masses, ensuring high purity raw materials for CZ single-crystal silicon production without requiring additional expensive purification steps.
Solution Approach 2:
The patent converts the harmful effect of electrode contamination into a beneficial process by deliberately removing the contaminated portion. The electrode-side end portion that would otherwise poison the silicon melt is extracted and discarded, transforming a potential harm into a controlled removal step that ensures high purity.
3Productivity
If the multi pulling method is used to improve productivity, then multiple single-crystal silicon ingots can be produced in one batch, but impurities accumulate in the silicon melt over multiple pulling cycles
Solution Approach 1:
The patent applies preliminary action by removing the electrode-side end portion containing heavy metal impurities before crushing. This ensures that the polycrystalline silicon masses added to the silicon melt during multi-pulling cycles remain free of impurities, preventing accumulation of contaminants even after multiple pulling operations.
Solution Approach 2:
The patent enables the production system to serve itself by producing high-purity polycrystalline silicon masses that can be repeatedly added to the silicon melt without introducing impurities. This self-service approach maintains melt purity throughout multiple pulling cycles, enabling sustained high productivity.
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 results in a high-purity polycrystalline silicon mass with reduced heavy metal impurities, preventing OSFs and extending minority carrier lifetime, suitable for producing high-quality CZ single-crystal silicon even after multiple pulling cycles.
Implementation Method 1
a silicon oxide coating using ozone water to reduce impurity concentrations
Implementation Method 2
using a polyethylene bag to minimize contamination during extraction and crushing
Data Source
AI summary
A clean and high-purity polycrystalline silicon mass having a small content of chromium, iron, nickel, copper, and cobalt in total, which are heavy metal impurities that reduce the quality of single-crystal silicon, can be obtained from a silicon rod by before crushing a polycrystalline silicon rod, removing at least 70 mm of a polycrystalline silicon portion from the electrode side end of the polycrystalline silicon rod extracted to the outside of a reactor is provided. Thereby, the polycrystalline silicon portion in which the total of the chromium, iron, nickel, copper, and cobalt concentrations in a bulk is not less than 150 ppta can be removed.