Scanning Metrology Target Layout for Time-Varying Overlay Errors
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Solution Overview
Problem
Increasing sampling requirements in semiconductor manufacturing for on-product metrology, such as overlay metrology, negatively impact metrology throughput due to higher complexity and time-varying errors in scanning metrology tools.
Innovation Solution
Design of scanning metrology targets with measurement groups of cells distributed along a transverse direction orthogonal to the scan direction, allowing simultaneous measurement of cells within each group to mitigate time-varying errors and enhance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sampling requirements are increased to meet shrinking design rules and demanding specifications, then measurement accuracy is improved, but metrology throughput deteriorates
Solution Approach 1:
The metrology target is divided into multiple measurement groups (first measurement group, second measurement group, etc.), each containing cells distributed along the transverse direction. This segmentation allows the scanning tool to measure different groups sequentially during a single scan, effectively increasing the number of measurements without requiring additional scan operations, thus improving throughput while maintaining accuracy
Solution Approach 2:
Cells within each measurement group are distributed along the transverse direction (orthogonal to scan direction) rather than along the scan direction. This spatial arrangement in a different dimension enables simultaneous measurement of multiple cells during a single scan pass, increasing sampling density without proportionally increasing measurement time
2Measurement precision
If more cells are measured simultaneously to increase sampling, then measurement accuracy is improved, but time-varying errors increase
Solution Approach 1:
Instead of measuring all cells simultaneously across the entire target, the patent measures cells in partial groups during sequential scan passes. Each measurement group contains a manageable number of cells that can be measured with minimal time-varying error impact, while still providing sufficient sampling statistics when multiple groups are combined
Solution Approach 2:
The metrology target is pre-configured with multiple measurement groups arranged in specific spatial locations along the scan direction. This preliminary arrangement allows the scanning system to efficiently select and measure appropriate groups during each scan pass, optimizing the balance between sampling density and measurement time while minimizing time-varying errors
Data Source
AI summary
A metrology system may include a controller coupled to a scanning metrology tool that images a sample in motion along a scan direction. The controller may receive an image of a metrology target on the sample from the scanning metrology tool, where the metrology target comprises a first measurement group including cells distributed along a transverse direction orthogonal to the scan direction, and a second measurement group separated from the first measurement group along the scan direction including cells distributed along the transverse direction. The controller may further generate at least a first metrology measurement based on at least one of the cells in the first measurement group, and generate at least a second metrology measurement based on at least one of the cells in the second measurement group.