Multi-Resolution Overlay Metrology Target for Semiconductor Substrates
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Solution Overview
Problem
Current semiconductor circuit metrology tools face challenges in accurately measuring overlay error due to discrepancies between different field of view sizes and the size of overlay targets, leading to reduced signal-to-noise ratios and potential loss of resolution, especially when using tools with wide and narrow fields of view simultaneously.
Innovation Solution
A composite overlay target with a small first sub-target and a large second sub-target, where the first sub-target is surrounded by and concentric with the second sub-target, is used to match the dimensions and feature sizes to both narrow-FOV and wide-FOV tools, allowing for accurate measurement of overlay error using separate or combined imaging from each tool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single overlay target is used for both narrow-FOV and wide-FOV tools, then device complexity is reduced, but measurement precision deteriorates due to mismatch between target size and field of view
Solution Approach 1:
The overlay target is segmented into multiple sub-targets with different sizes (e.g., a first sub-target and a second sub-target). Each sub-target is optimized for specific field of view requirements, allowing narrow-FOV tools to use the smaller sub-target and wide-FOV tools to use the larger sub-target, thereby resolving the measurement precision issue while maintaining a unified target structure
Solution Approach 2:
The composite overlay target structure serves multiple functions simultaneously by incorporating sub-targets of different dimensions within a single target. This multi-functional design enables the same physical target to be used by both narrow-FOV and wide-FOV measurement tools, eliminating the need for separate targets and reducing overall device complexity
2Measurement precision
If overlay target features are made small to match narrow-FOV tools, then measurement precision for narrow-FOV tools is improved, but signal-to-noise ratio deteriorates when using wide-FOV tools
Solution Approach 1:
Different regions of the overlay target (different sub-targets) have different local qualities in terms of feature size. The smaller sub-target has features optimized for narrow-FOV tools with appropriate signal density, while the larger sub-target has features scaled appropriately for wide-FOV tools, ensuring optimal signal-to-noise ratio for each tool type without compromising the other
3Loss of information
If overlay target features are made large to match wide-FOV tools, then signal-to-noise ratio for wide-FOV tools is improved, but measurement precision deteriorates for narrow-FOV tools
Solution Approach 1:
The target is divided into segmented sub-targets where the larger sub-target provides adequate signal-to-noise ratio for wide-FOV tools, while the smaller sub-target within the same structure provides the fine detail resolution required by narrow-FOV tools, thus resolving the precision deterioration issue
Data Source
AI summary
A product includes at least one semiconductor substrate, multiple thin-film layers disposed on the at least one substrate, and an overlay target formed in at least one of the thin-film layers. The overlay target includes a first sub-target having a first center of symmetry and including first target features having a first linewidth, and a second sub-target having a second center of symmetry coincident with the first center of symmetry and including second target features, which have a second linewidth, greater than the first linewidth, and are adjacent to but non-overlapping with the first target features.