Silicon Trace Metal Analysis Using Zone-Melt Drop Concentration
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Solution Overview
Problem
Existing methods for determining metallic impurities in silicon, such as INAA and freeze-tip methods, suffer from high costs, complex instrumentation, long analysis times, low recovery rates, and contamination issues, making them unsuitable for routine and efficient analysis.
Innovation Solution
A method involving zone melting with a reversed movement of the silicon sample and seed crystal to form a conical end region, followed by cooling and partial dissolution of a solidified silicon drop, allowing for high recovery rates and reduced contamination, using a controlled etching process to analyze the impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If instrumental neutron activation analysis (INAA) is used to determine metallic impurities, then detection limits are very low (≤50 pg/g for Fe, Cr, Ni), but the analysis duration is very long (2 to 3 months) and the cost is very high
Solution Approach 1:
The invention applies preliminary action by performing zone melting to concentrate impurities into a small volume (the solidified drop) before analysis. This pre-concentration step enables rapid analysis with low detection limits, eliminating the need for long INAA measurement periods while achieving comparable or better sensitivity.
Solution Approach 2:
The invention changes the physical state and concentration parameters of the sample by melting silicon and concentrating impurities into a small solidified drop. This parameter change from bulk analysis to concentrated drop analysis enables both low detection limits and rapid analysis times.
2Productivity
If the freeze-tip method is used to concentrate and analyze metallic impurities, then analysis time is reduced to less than a week, but the recovery rate of impurities is low and contamination occurs during mechanical separation
Solution Approach 1:
The invention extracts impurities from the bulk silicon by concentrating them into a separate solidified drop through controlled zone melting. This extraction eliminates the need for mechanical separation that causes contamination and loss, achieving both high recovery rates and fast analysis.
Solution Approach 2:
Instead of mechanically separating and then analyzing impurities as in the freeze-tip method, the invention inverts the approach by first concentrating impurities into a solidified drop through controlled freezing, then analyzing the drop without mechanical separation. This inversion eliminates contamination while maintaining fast analysis.
3Measurement precision
If zone melting is used to concentrate impurities, then detection limits are improved, but the process complexity and instrumentation requirements increase
Solution Approach 1:
The invention uses a simple, disposable solidified drop containing concentrated impurities instead of complex, expensive instrumentation. The drop serves as a temporary, single-use sample preparation that enables sensitive detection with minimal equipment, replacing costly INAA or complex ICP-MS setups.
4Productivity
If complete dissolution of silicon sample is performed to analyze impurities, then analysis time is short (1 to 2 days), but detection limits are 100 times greater than INAA due to lack of concentration
Solution Approach 1:
The invention performs preliminary concentration of impurities into a small solidified drop before dissolution and analysis. This pre-concentration enables both rapid analysis and low detection limits by ensuring impurities are concentrated in a small volume that dissolves quickly but maintains high impurity concentration for sensitive detection.
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
Achieves high recovery rates of up to 95% of metallic impurities in a solidified silicon drop, reducing analysis time and contamination, and lowering detection limits, making it suitable for routine and cost-effective analysis.
Implementation Method 1
zone melting (zone pulling) to form a single silicon crystal having a conical end region, with a droplike melt forming at the end of the single silicon crystal
Implementation Method 2
remelting of the silicon sample to reduce its diameter
Implementation Method 3
cooling of the droplike melt to form a solidified silicon drop
Implementation Method 4
partial or complete dissolution of the silicon drop in an acid
Implementation Method 5
controlled etching process to analyze the impurities
Data Source
AI summary
A method for determining an amount of metallic impurities within silicon. The method includes the steps of (a) providing a rodlike silicon sample and a rodlike seed crystal in a zone melting apparatus, (b) zone melting to form a single silicon crystal having a conical end region with a droplike melt forming at the end of the single silicon crystal in a separation step, (c) cooling of the droplike melt to form a solidified silicon drop, (d) partial or complete dissolution of the silicon drop in an acid, and analyzing the solution obtained in step (d) by a trace analysis technique. Wherein the separation step further includes a remelting step for the silicon sample to reduce its diameter, forming a droplike melting zone, and separation of the seed crystal and the silicon sample by moving the seed crystal and the silicon sample apart from one another.