Transparent Wafer Defect Detection With Chuck Pattern Suppression
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Solution Overview
Problem
Existing defect detection systems struggle to effectively distinguish defects on transparent or translucent wafers due to interference from chuck components, leading to poor sensitivity and throughput, especially when chuck patterns and surface roughness obscure defects.
Innovation Solution
A two-step defect detection method using local reference pixels within the same die, combining mean and median calculations to enhance sensitivity and speed, and independent bright and dark field channel analysis to suppress chuck patterns and improve defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional defect detection algorithms are used on transparent or translucent wafers, then the system can process images, but the chuck components (patterns and surface roughness) obscure the defects, leading to poor detection sensitivity
Solution Approach 1:
The patent divides the defect detection process into two separate channels: bright field imaging for detecting chuck patterns and dark field imaging for detecting defects. This segmentation allows each channel to specialize in detecting specific features, preventing the chuck patterns from obscuring the defects in the final detection result.
Solution Approach 2:
The patent introduces an intermediary processing step where the bright field image (containing chuck patterns) is used to generate a mask or reference that is then applied to the dark field image. This intermediary step effectively removes or suppresses the chuck pattern interference before defect detection occurs.
2Productivity
If existing defect detection tools are used to achieve defect detection on transparent wafers, then some defects can be detected, but the throughput and inspection sensitivity targets cannot be met due to the need for complex image processing
Solution Approach 1:
The patent segments the imaging system into two parallel channels (bright field and dark field) that operate simultaneously. This allows defect detection to proceed without requiring complex sequential image processing, as each channel provides complementary information that can be combined through simple logical operations, thereby maintaining high throughput.
Solution Approach 2:
The patent changes the imaging parameters by using two different field conditions (bright and dark) rather than relying on a single imaging mode. This parameter change enables the system to detect both chuck patterns and defects efficiently without increasing processing complexity, as the dual-channel approach processes images in parallel rather than requiring complex sequential analysis.
Data Source
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AI summary
Defect detection on transparent or translucent wafers can be performed on a die using references from the same die. A first calculated value based on a kernel size, such as a moving mean, is determined. A first difference is determined by subtracting the first calculated value from a pixel intensity. Candidate pixels with a first difference above a threshold are classified. A second calculated value based on a kernel size, such as a local median, is determined. A second difference is determined by subtracting the second calculated value from the pixel intensity. Pixels that include a defect are classified when the second difference is above the threshold.