Wafer Inspection Using Focus Offset Defect Separation
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Solution Overview
Problem
Current inspection methods for semiconductor wafers struggle to accurately distinguish between defects on underlying and uppermost layers, leading to difficulties in separating current layer defect signals from previous layer signals, which results in lower productivity and sensitivity to coordinate inaccuracy.
Innovation Solution
The method involves performing different scans of the wafer with varying focus offsets to detect and compare defects, determining if they belong to the underlying or uppermost layer based on changes in signal magnitude, allowing for the separation of defects without prior inspection results and improving sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If brightfield inspection is used to detect defects on a wafer, then throughput and sensitivity are improved, but defects of underlying layers are detected and dominate the inspection results making analysis difficult
Solution Approach 1:
The inspection process is segmented into multiple focus offsets. By dividing the inspection into different focal planes (first focus offset for underlying layer, second focus offset for uppermost layer), the method separates defect signals from different layers, allowing brightfield inspection to be used without being overwhelmed by underlying layer defects.
Solution Approach 2:
The patent introduces the focus offset dimension to separate defects. By inspecting at different focal planes (adding a dimensional parameter), defects from different layers can be distinguished even when using brightfield configuration, transforming a 2D inspection problem into a 3D focus-space problem.
2Measurement precision
If defect source analysis is performed by inspecting at two different levels to filter common events, then separation of current layer defects is improved, but productivity decreases due to additional inspection steps
Solution Approach 1:
The patent merges the defect separation function into a single inspection process by using multiple focus offsets within one inspection pass. Instead of requiring separate inspections at different process levels, the method combines layer separation capability into one inspection operation, maintaining productivity while achieving defect source analysis.
Solution Approach 2:
The inspection process performs preliminary separation of defects by focus offset within a single inspection pass. By pre-establishing the focus offset relationship between underlying and uppermost layers, the system can immediately distinguish defect sources without requiring subsequent separate inspections or complex post-processing.
3Loss of information
If multiple inspections are performed at different process levels, then defect source analysis is possible, but coordinate inaccuracy between inspections reduces result reliability
Solution Approach 1:
The single inspection tool is made universal by enabling it to perform both underlying layer and uppermost layer defect detection through multiple focus offsets. Since the same inspection tool and coordinate system are used for both focus offsets, coordinate accuracy is maintained while achieving multi-layer defect source analysis.
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 enhances the ability to detect only the defects of interest, improving productivity and accuracy by eliminating previous layer noise, and enabling the use of brightfield inspection for critical layers previously inaccessible due to nuisance defect detection.
Implementation Method 1
a brightfield configuration is used to detect light reflected specularly from a wafer
Implementation Method 2
a darkfield configuration is used to detect light scattered from a wafer
Data Source
AI summary
Methods and systems for inspection of a wafer or setting up an inspection process are provided. One method for inspection of a wafer includes detecting first and second sets of defects on the wafer by performing different scans of the wafer with different focus offsets. The method also includes comparing results of the different scans for a defect of the first set and a defect of the second set that are detected at approximately the same location on the wafer. The method further includes determining if the defect of the first and second sets is a defect of an underlying layer or an uppermost layer formed on the wafer based on results of the comparing step.