SPV Fe Measurement in P-Type Silicon Under Ion-Controlled Air
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Solution Overview
Problem
Conventional SPV measurement methods struggle with achieving sufficient measurement accuracy for iron (Fe) concentrations of 1×10^9/cm^3 or less in p-type silicon wafers, as the measurement values vary significantly even in controlled environments, and environmental factors other than temperature, humidity, and cleanliness are not adequately considered.
Innovation Solution
The method involves optimizing the environment by controlling the ion concentration, specifically setting the total concentration of Na+, NH4+, and K+ to 1.750 μg/m^3 or less, and the total concentration of F−, Cl−, NO2−, PO43−, Br−, NO3−, and SO42− to 0.552 μg/m^3 or less, and reducing organic concentration to 0.05 μg/cm^2 or less, using chemical filters to maintain these conditions within the SPV measurement apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SPV measurement is performed in conventional recommended environment (temperature: 24±2°C, relative humidity: 30% to 50%, cleanliness: class 7), then measurement is non-contact and non-destructive with shorter measurement time, but measurement accuracy for Fe concentrations of 1×10^9/cm^3 or less is insufficient and values vary significantly
Solution Approach 1:
The patent extends environmental control parameters beyond conventional temperature, humidity, and cleanliness to include ion concentration (controlling Na+, NH4+, K+, F−, Cl−, NO2−, PO43−, Br−, NO3−, and SO42−) and organic concentration. By adding these parameter controls, measurement accuracy for low Fe concentrations is improved without significantly increasing system complexity
Solution Approach 2:
The patent implements preliminary control of ion and organic concentrations in the measurement environment before performing SPV measurements. Chemical filters are installed and pre-configured to maintain specified ion concentration (≤1.750 μg/m^3 for cations, ≤0.552 μg/m^3 for anions) and organic concentration (≤0.05 μg/cm^2), ensuring accurate measurements of low Fe concentrations from the outset
2Measurement precision
If ion concentration and organic concentration in measurement environment are controlled to specified levels, then measurement accuracy for Fe concentrations of 1×10^9/cm^3 or less is significantly improved, but environmental control system becomes more complex
Solution Approach 1:
The patent introduces chemical filters as intermediary devices between the external environment and the SPV measurement apparatus. These filters mediate the ion and organic concentration levels, automatically maintaining the required environmental conditions (ion concentration ≤1.750 μg/m^3 for cations, ≤0.552 μg/m^3 for anions; organic concentration ≤0.05 μg/cm^2) without requiring complex active control systems
Solution Approach 2:
The chemical filters operate autonomously to maintain specified ion and organic concentrations in the measurement environment. The system self-regulates by allowing the filters to passively remove ions and organic contaminants from the air, eliminating the need for complex monitoring and adjustment mechanisms while ensuring measurement accuracy
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 improves the measurement accuracy for Fe concentrations of 1×10^9/cm^3 or less by stabilizing the diffusion length measurement and reducing variations, ensuring reliable quantification of Fe concentrations.
Implementation Method 1
a p-type silicon wafer is illuminated with lights of certain wavelengths, and the surface photovoltage (SPV signal) of the wafer of that time is measured to determine the diffusion length of minority carriers in the wafer
Data Source
AI summary
A method of measuring the concentration of Fe in a p-type silicon wafer by an SPV method enabling improvement in the measurement accuracy for Fe concentrations of 1×109/cm3 or less. The method of measuring the concentration of Fe in a p-type silicon wafer includes measuring an Fe concentration in the p-type silicon wafer based on measurement using an SPV method. The measurement is performed in an atmosphere in which the total concentration of Na+, NH4+, and K+ is 1.750 μg/m3 or less, and the total concentration of F−, Cl−, NO2−, PO43−, Br−, NO3−, and SO42− is 0.552 μg/m3 or less.