Moiré Overlay Target Design for Large Range Measurement
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Solution Overview
Problem
Existing overlay metrology techniques using periodic targets have a limited measurable range of overlay values, leading to ambiguous measurements when physical overlay errors exceed this range.
Innovation Solution
The implementation of an overlay metrology system that utilizes Moiré structures formed from first-layer and second-layer features with different pitches, allowing for the determination of coarse and fine overlay measurements, which are then combined to generate an accurate output overlay measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If periodic overlay targets are used, then overlay measurement can be performed, but the measurable range of overlay values is limited and ambiguous measurements occur when physical overlay errors exceed the range
Solution Approach 1:
The overlay target is divided into multiple Moiré structures, each capable of measuring a specific range of overlay values. By segmenting the measurement task across multiple structures with different pitch combinations, the system achieves both high precision for small overlays and extended range for large overlays without ambiguity.
Solution Approach 2:
The patent introduces a new dimension to overlay measurement by using Moiré structures with different pitch combinations (e.g., 10nm/20nm, 20nm/40nm) rather than relying on a single periodic structure. This multi-scale approach allows the system to resolve overlay values beyond the traditional limited range while maintaining measurement precision.
2Adaptability or versatility
If Moiré structures with different pitches are used, then the measurable overlay range is extended, but the complexity of the overlay target increases
Solution Approach 1:
Each Moiré structure in the overlay target serves multiple functions: it provides both coarse overlay information through its pitch combination and fine overlay information through its Moiré fringe patterns. This multi-functionality allows the system to achieve extended range without proportionally increasing complexity, as each structure contributes to both range extension and measurement precision.
Solution Approach 2:
Different regions of the overlay target are designed with locally optimized Moiré structures having specific pitch combinations tailored to their measurement requirements. This allows each local region to be optimized for its specific overlay range while the overall target maintains a manageable structure through localized specialization.
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 enables accurate overlay measurements over a large range of physical overlay values, resolving ambiguities associated with traditional periodic targets by leveraging the overlap and non-overlap regions of the Moiré structures.
Implementation Method 1
the overlay target includes one or more Moiré structures, where a respective one of the one or more Moiré structures is formed from first-layer features with a first pitch on a first layer of the sample and further with second-layer features with a second pitch on a second layer of the sample, where the first-layer features and the second-layer features in the respective one of the one or more Moiré structures partially overlap
Data Source
AI summary
An overlay metrology system may receive images of an overlay target on a sample, where the overlay target includes Moiré structures in which first-layer features and second-layer features partially overlap, where overlap regions include regions of overlap between the first-layer and second-layer features, where non-overlap regions include regions of non-overlap between the first-layer and second-layer features. The system may further, determine a coarse overlay measurement based at least in part on the one or more non-overlap regions of the one or more images, determine a fine overlay measurement based at least in part on the one or more overlap regions of the one or more images, and generate an output overlay measurement based on the coarse overlay measurement and the fine overlay measurement.