Polysilicon Washing Conductivity Control
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Solution Overview
Problem
Current methods for washing polycrystalline silicon to remove residual acid solutions are inefficient, as they rely on pH or ion concentration measurements, which are inaccurate at low concentrations and laborious, and fail to precisely determine the completion of the water cleaning step, leading to incomplete removal of contaminants.
Innovation Solution
A method involving the replacement of pure water in the water cleaning bath after acid cleaning, with electrical conductivity measurement to assess acid concentration, ensuring the water cleaning step is completed when conductivity reaches 2 µS/cm or lower, and an apparatus with a water drainage device, pure water supplying device, and electrical conductivity measuring device to facilitate this process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pH or ion concentration measurement is used to determine completion of water cleaning, then the process can be monitored, but the measurement accuracy is insufficient at low acid concentrations
Solution Approach 1:
The patent changes the measurement parameter from pH or ion concentration to electrical conductivity. Electrical conductivity provides superior measurement accuracy at low acid concentrations compared to pH or ion concentration methods, enabling reliable determination of water cleaning completion even when acid concentration is extremely low (e.g., 0.1 mg/L or less).
Solution Approach 2:
The patent replaces the chemical measurement methods (pH measurement, ion concentration measurement) with an electrical measurement method (electrical conductivity measurement). This substitution enables more accurate and rapid assessment of acid concentration in the water cleaning bath.
2Manufacturing precision
If pure water is replaced multiple times to ensure complete acid solution removal, then cleanliness is improved, but processing time and water consumption increase
Solution Approach 1:
The patent implements a feedback control system where electrical conductivity of the pure water is continuously or periodically measured during the water cleaning process. Based on the measured conductivity value, the system determines when acid solution removal is complete (e.g., when conductivity reaches a predetermined threshold), allowing the process to stop at the optimal point without unnecessary additional water replacements or time extension.
Solution Approach 2:
The patent establishes predetermined conductivity thresholds and replacement criteria before the water cleaning process begins. These preliminary parameters guide the water replacement process, enabling systematic and efficient removal of acid solutions without requiring excessive water replacements or time.
3Loss of information
If ion concentration measurement is used to evaluate acid solution removal, then some information is obtained, but the measurement process is time-consuming
Solution Approach 1:
The patent replaces the time-consuming ion concentration measurement method with a rapid electrical conductivity measurement method. Electrical conductivity can be measured instantly or near-instantaneously, providing real-time feedback on acid concentration without the lengthy processing required by ion concentration analysis.
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 allows for accurate and efficient removal of residual acid solutions, ensuring high cleanliness of polycrystalline silicon by precisely determining the completion of the water cleaning step, even at low acid concentrations, thereby improving the quality of the silicon.
Implementation Method 1
measuring the electrical conductivity of the pure water and evaluating the concentration of acid
Implementation Method 2
the surface of polycrystalline silicon is dissolved, thereby the contaminants and oxide films are removed
Data Source
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AI summary
A method of washing polycrystalline silicon is provided. The method includes a step of acid cleaning in which the polycrystalline silicon is cleaned with an acid solution and a step of a water cleaning in which the polycrystalline silicon is cleaned by pure water after the step of acid cleaning. In the step of water cleaning, residual acid solution on the surface of the polycrystalline silicon is removed by immersing the polycrystalline silicon in pure water held in a water cleaning bath, and replacing the pure water in the water cleaning bath at least once. The electrical conductivity (C) of the pure water in the water cleaning bath is measured. Based on the reading of the electrical conductivity (C), the timing for finishing the step of water cleaning is decided.