Silicon Wafer Impurity Analysis via Surface-Bulk Calibration
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Solution Overview
Problem
Current methods for analyzing impurities in silicon wafers, particularly nickel contamination, are inadequate as they either focus on surface analysis, require extensive time and costly chemicals, or fail to accurately quantify bulk contamination.
Innovation Solution
A method involving two evaluation silicon wafers with varying degrees of contamination, where one wafer's surface layer is dissolved with hydrofluoric acid for surface impurity measurement and the other's bulk portion is analyzed post-cleaving, with results used to create a calibration curve for determining bulk impurity concentrations without destroying the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods (TXRD, SIMS, AAS, ICP-MS) are used to analyze impurities in silicon wafers, then measurement precision is improved, but the cost of chemical solutions and time required increases significantly
Solution Approach 1:
The patent applies preliminary action by pre-contaminating evaluation silicon wafers with known concentrations of nickel impurities before analysis. This creates a calibration curve in advance that relates surface impurity concentrations to bulk impurity concentrations, eliminating the need for time-consuming bulk analysis of every sample during actual testing.
Solution Approach 2:
The patent uses evaluation silicon wafers as copies or proxies for actual silicon wafers. By analyzing the surface impurity concentrations of these evaluation wafers and referencing the pre-established calibration curve, the bulk impurity concentrations of actual wafers can be determined indirectly without performing full bulk analysis on each sample.
2Measurement precision
If conventional methods use large quantities of acid to dissolve silicon wafers for bulk analysis, then measurement precision is improved, but the cost of chemical solutions increases
Solution Approach 1:
The patent replaces the need to physically dissolve and analyze bulk material with a copying approach. The calibration curve created from evaluation wafers serves as a reference model that allows bulk impurity concentrations to be determined from surface measurements alone, eliminating the need for acid dissolution of actual samples.
Solution Approach 2:
The patent extracts only the necessary information (surface impurity concentration) from the silicon wafer surface using minimal acid, rather than dissolving the entire bulk material. The calibration curve then provides the extracted bulk impurity concentration information without requiring physical extraction of bulk material.
3Measurement precision
If surface layer analysis is performed using hydrofluoric acid dissolution, then surface impurity measurement precision is improved, but the ability to measure bulk impurities is lost
Solution Approach 1:
The patent establishes a feedback relationship through the calibration curve that connects surface impurity measurements to bulk impurity concentrations. By measuring surface impurities and referencing the calibration curve (which was created by correlating surface and bulk measurements from evaluation wafers), bulk impurity information is recovered without directly analyzing the bulk.
Solution Approach 2:
The calibration curve is created in advance through preliminary action, establishing the relationship between surface and bulk impurity concentrations. This pre-established relationship enables bulk impurity determination from surface measurements alone during actual analysis, preventing loss of bulk information.
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
Enables accurate measurement of nickel contamination in both surface and bulk layers of silicon wafers, reducing the need for extensive acid use and time, while providing a cost-effective and non-destructive analysis.
Implementation Method 1
a step of dissolving a surface layer portion of either one of the evaluation silicon wafers with a solution including hydrofluoric acid, and measuring a concentration of impurities included in the solution
Data Source
AI summary
This method for analyzing impurity includes: a step of immersing each of sets of two evaluation silicon wafers into a washing solution, thereby contaminating the evaluation silicon wafers to be in a same state of contamination; a step of dissolving each of a surface layer portion of either one of the evaluation silicon wafers and a bulk portion of the other evaluation silicon wafer with solutions including hydrofluoric acid respectively, and measuring a concentration of impurities included in each of the solutions; a step of determining a calibration curve that shows a relation between the concentrations of the impurities in the surface layer portions and the concentrations of the impurities in the bulk portions of the evaluation silicon wafers; a step of dissolving a surface layer portion of a silicon wafer of a test object with a solution including hydrofluoric acid, and measuring a concentration of impurities included in the solution; and a step of determining a concentration of impurities in a bulk portion based on the calibration curve using the measured concentration of the impurities.