Wafer Debris Detection by Regional Flatness Statistics
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Solution Overview
Problem
Conventional methods for detecting debris around hard laser marks on silicon wafers are inaccurate due to the narrow dynamic range of flatness measuring instruments, leading to incorrect measurements and inability to distinguish local thickness variations caused by debris.
Innovation Solution
A debris determination method that involves measuring thickness unevenness parameters in regions with and without hard laser marks, calculating statistical values such as mean, standard deviation, and comparing these values to determine the presence of debris by setting a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrow dynamic range flatness measuring instrument is used to accurately measure wafer flatness, then measurement precision is improved, but the instrument cannot measure steep shape changes caused by debris
Solution Approach 1:
The measurement data is segmented into multiple regions: a first region containing the hard laser mark and a second region excluding it. By calculating statistical values separately for each region and comparing them, the method can detect local thickness variations (debris) without being affected by the narrow dynamic range limitation of the measuring instrument.
Solution Approach 2:
The invention transitions from direct absolute height measurement to statistical comparison of relative thickness variations. By computing statistical values (mean, standard deviation, etc.) of thickness unevenness in different regions and comparing their differences, the method detects debris in a different dimensional approach that bypasses the dynamic range limitation.
2Ease of operation
If ESFQR parameter is used to detect debris, then measurement is simplified, but detection accuracy deteriorates due to inclusion of inaccurate extreme values
Solution Approach 1:
The measurement region is segmented into a first region (including hard laser mark) and a second region (excluding it). Statistical values are calculated separately for each segment, allowing localized debris detection without contamination from extreme values in other regions.
Solution Approach 2:
The method applies different evaluation criteria to different regions: the first region statistical values are specifically compared against the second region statistical values to detect local abnormalities (debris) at the hard laser mark location, rather than evaluating the entire wafer surface uniformly.
3Measurement precision
If laser microscope is used for high resolution evaluation, then measurement precision is improved, but productivity deteriorates due to low throughput and destructive testing
Solution Approach 1:
The flatness measuring instrument, already used for general wafer flatness measurement, is made multi-functional by applying statistical comparison methods to also detect debris. This eliminates the need for separate high-resolution laser microscope evaluation, maintaining productivity while achieving debris detection capability.
Solution Approach 2:
The invention changes the evaluation parameters from direct high-resolution imaging to statistical analysis of thickness unevenness parameters. By transforming the measurement approach from spatial resolution-dependent to statistical variation-dependent, the method achieves debris detection using standard flatness measurement equipment.
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
Accurately detects the presence of debris by reflecting the amount of change in measurement values within the dynamic range, preventing the release of wafers with debris to customers.
Implementation Method 1
a method to use an optical interferometric flatness measuring instrument (WaferSight manufactured by KLA Corporation)
Data Source
AI summary
A debris determination method of determining presence or absence of debris occurrence around hard laser mark after hard laser mark is formed on a back surface of wafer or after back surface of wafer is polished after formation of hard laser mark, wherein thickness unevenness parameter of wafer is measured by flatness measuring instrument, and statistical data on thickness unevenness parameter of region including hard laser mark (referred to as region A) is extracted, along with statistical data on a thickness unevenness parameter of a region adjacent to the region A (referred to as region B) is extracted and statistical data of region A and statistical data of region B are compared and a difference is calculated, when the difference is equal to or greater than a predetermined threshold, debris is determined to occur. This provides debris determination method that can accurately detect a local thickness variation due to debris.