Polycrystalline Silicon Purification via GC/MS-SIM Impurity Detection
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Solution Overview
Problem
Conventional methods for producing high-purity polycrystalline silicon struggle with the detection and removal of carbon impurities, particularly methylchlorosilanes, due to limitations in detection sensitivity and the inability to simultaneously separate chlorosilanes and hydrocarbons, leading to suboptimal purification levels.
Innovation Solution
The use of the GC/MS-SIM method with a non-polar and medium-polar column combination for analyzing chlorosilanes, allowing for the detection of carbon-containing impurities at lower concentrations, specifically targeting methyldichlorosilane and isopentane, ensures that only trichlorosilane meeting stringent quality criteria is used as a raw material for CVD processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional distillation purification is used for trichlorosilane, then the purification process is relatively simple, but carbon-containing impurities such as methyldichlorosilane cannot be effectively removed due to close boiling points
Solution Approach 1:
The patent changes the detection parameter from conventional GC-FID to GC/MS-SIM, which enables detection of carbon-containing impurities at much lower concentrations (0.01 ppmw or lower). This parameter change in detection sensitivity allows for effective quality control without requiring complex additional purification steps, as impurities can be detected and controlled at trace levels.
Solution Approach 2:
The patent replaces the reliance on mechanical distillation separation (which fails due to close boiling points) with a chemical analysis and quality control system using GC/MS-SIM. This substitution allows for identification and control of impurities based on their chemical signature rather than physical separation, effectively bypassing the limitation of similar boiling points.
2Measurement precision
If GC-FID method is used for analyzing carbon impurities, then the analysis process is simple, but the detection sensitivity is insufficient to detect impurities at required low concentrations
Solution Approach 1:
The patent changes the detection method from GC-FID to GC/MS-SIM, which provides significantly higher detection sensitivity. The MS-SIM mode allows for selective ion monitoring that can detect impurities at 0.01 ppmw or lower concentrations, meeting the stringent requirements for semiconductor-grade silicon production.
Solution Approach 2:
The patent introduces mass spectrometry as an intermediary detection system between the gas chromatography separation and the final detection. This intermediary provides highly specific identification of carbon-containing impurities through their mass-to-charge ratio, enabling detection at trace levels that conventional FID cannot achieve.
3Adaptability or versatility
If single-column GC analysis is used, then the analysis is simple, but simultaneous separation of chlorosilanes and hydrocarbons cannot be achieved
Solution Approach 1:
The patent segments the chromatography system into two columns with different polarities (non-polar and medium-polar) connected in series. This segmentation allows each column to specialize in separating different types of compounds - the non-polar column for hydrocarbons and the medium-polar column for chlorosilanes - achieving simultaneous separation of both compound classes.
Solution Approach 2:
The patent uses a composite chromatography system combining two different column types with distinct polarity characteristics. This composite approach leverages the complementary separation mechanisms of non-polar and medium-polar columns to achieve broad-spectrum separation capability for both hydrocarbons and chlorosilanes in a single analytical run.
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 significantly enhances the purification of polycrystalline silicon by excluding chlorosilanes with excessive carbon impurities, achieving a carbon concentration of less than 0.05 ppma, thereby improving the electrical properties and reducing defects in semiconductor-grade silicon.
Implementation Method 1
a quality determination is performed by analyzing a content of methyldichlorosilane and isopentane by GC/MS-SIM method
Implementation Method 2
The use of the GC/MS-SIM method with a non-polar and medium-polar column combination for analyzing chlorosilanes, allowing for the detection of carbon-containing impurities at lower concentrations
Implementation Method 3
produce a high-purity polycrystalline silicon containing carbon of lower than 0.05 ppma using chlorosilanes by CVD method
Data Source
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AI summary
The present invention provides technology for realizing higher purification of a polycrystalline silicon. First, trichlorosilane is prepared as a sample (S101) and then the carbon-containing impurities content in the trichlorosilane is analyzed by GC/MS-SIM method (S102). The quality of the trichlorosilane is determined based on the analysis results (S103) and the trichlorosilane determined to be a good material (S103:Yes) is used as the raw material for producing a high-purity polycrystalline silicon by CVD method (104). In case, the trichlorosilane determined to be a bad material (S103: No) is not used as the raw material for producing a polycrystalline silicon. When the impurities analysis by GC/MS-SIM method is performed using, as a separation column, a column having a non-polar column and a medium-polar column connected in series with each other, it is possible to simultaneously perform both of the separation of chlorosilanes and hydrocarbons and the separation of chlorosilanes and methylsilanes.