Semiconductor Wafer Gettering Property Evaluation via Polishing Marks
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Solution Overview
Problem
Current methods for evaluating the gettering property of semiconductor wafers are laborious and unsuitable for evaluating wafers that can become actual products, as they involve contaminating the wafer with metallic elements and are not efficient for assessing the gettering property in device wafers intended for production.
Innovation Solution
A method that involves polishing the back surface of semiconductor wafers to form gettering layers and counting the number of polishing marks within a specific width range on the back surface, using a polishing wheel and imaging system to determine the gettering property by comparing the count to a predetermined value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the back surface of a device wafer is polished to reduce thickness to or below 100 μm, then the wafer thickness is reduced for making devices smaller, but the gettering effect for trapping metallic elements is lowered
Solution Approach 1:
The invention applies local quality by creating a gettering layer with different properties than the bulk wafer material. Through controlled polishing that generates subsurface damage, a localized region with enhanced gettering capability is formed at the back surface, allowing the thin wafer to maintain trapping ability for metallic elements like Cu in the gettering layer while keeping the front surface intact for device functionality.
2Measurement precision
If the conventional evaluation method is used to measure gettering property by contaminating the wafer with metallic elements, then the gettering property can be measured, but the evaluation becomes laborious and device wafers cannot be used for evaluation
Solution Approach 1:
The invention replaces the complex mechanical/chemical process of contaminating wafers with metallic elements and measuring atom amounts with a simplified optical measurement system. By correlating gettering property with polishing mark characteristics (width, density, distribution), the method substitutes direct compositional analysis with surface morphology observation, enabling rapid evaluation without wafer contamination.
Solution Approach 2:
The invention creates a visual copy or representation of the gettering layer quality through polishing marks on the back surface. These marks serve as indirect indicators that replicate the information about subsurface damage and gettering capability, allowing evaluation without directly measuring the metallic element trapping ability.
3Reliability
If polishing is performed to form a gettering layer, then the gettering property is improved, but the evaluation process becomes complex requiring contamination and precise atom measurement
Solution Approach 1:
The invention extracts the essential evaluation information from the complex contamination and measurement process by focusing solely on polishing mark characteristics. By taking out only the relevant visual features (mark width of 10-500 nm, density, distribution) that correlate with gettering quality, the method simplifies the evaluation to counting and measuring surface features rather than performing complex contamination and atom quantification procedures.
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 method allows for easy evaluation of the gettering property of semiconductor wafers that can become products, ensuring sufficient gettering performance by counting polishing marks, which correlates with the wafer's ability to trap metallic elements, thereby preventing device malfunctions.
Implementation Method 1
a gettering layer forming step of polishing a back surface opposite to the front surface of the semiconductor wafer by use of a polishing wheel to form polishing marks on the back surface and to form a gettering layer inside the semiconductor wafer and beneath the polishing marks
Data Source
AI summary
A gettering property evaluating method for a wafer includes: a gettering layer forming step of polishing a back surface opposite to a front surface of a semiconductor wafer by use of a polishing wheel to form polishing marks on the back surface and to form a gettering layer inside the semiconductor wafer and beneath the polishing marks; an imaging step of imaging at least a unit region of the back surface formed with the polishing marks by imaging means; a counting step of counting the number of the polishing marks having a width of 10 to 500 nm present in the unit region imaged; and a comparing step of comparing the number of the polishing marks counted by the counting step with a predetermined value to determine whether or not the counted number is not less than the predetermined value.