Moiré Metrology Targets for Overlay Error Detection
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Solution Overview
Problem
Current overlay metrology methods face challenges in sensitivity and robustness due to shrinking design rules and demanding specifications, necessitating improved metrology target designs and measurement techniques for accurate and efficient analysis of overlay errors between sample layers.
Innovation Solution
The development of a metrology target with rotationally symmetric Moiré patterns formed from grating structures with different pitches on multiple sample layers, allowing for the determination of overlay errors by analyzing the difference in axes of symmetry using a Moiré gain based on the pitches of the Moiré pattern, and a corresponding metrology system that adjusts for optical configurations to enhance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional overlay metrology methods are used, then measurement can be performed, but sensitivity and robustness are insufficient due to shrinking design rules
Solution Approach 1:
The patent transforms the overlay measurement from direct spatial measurement to Moiré fringe pattern analysis. By superimposing two gratings with slightly different pitches, the system creates Moiré fringes that amplify the overlay error signal, effectively converting a sub-resolution measurement problem into a resolvable optical interference pattern that can be detected with standard microscopy equipment.
Solution Approach 2:
The patent changes the measurement parameter from direct grating position to Moiré fringe characteristics (spacing, orientation, contrast). By measuring the Moiré fringe parameters rather than the original grating positions, the system achieves enhanced sensitivity to overlay errors while maintaining compatibility with existing optical systems and design rules.
2Measurement precision
If Moiré patterns with different pitches are used, then measurement sensitivity increases, but target design complexity increases
Solution Approach 1:
The metrology target is divided into multiple working zones, each containing a specific Moiré pattern configuration. This segmentation allows different regions to be optimized for different measurement requirements while maintaining overall target functionality. Each working zone can be independently designed and analyzed, simplifying the overall design process despite the complexity of Moiré patterns.
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 sensitive and robust overlay measurements by leveraging the increased shift of Moiré fringes, which are proportional to the overlay error, providing accurate overlay error calculations with improved sensitivity and robustness in metrology systems.
Implementation Method 1
at least one of the first pattern or the second pattern is a Moiré pattern formed from a first grating structure with a first pitch along a measurement direction on a first sample layer and a second grating structure with a second pitch along the measurement direction on a second sample layer
Data Source
AI summary
A metrology target may include a first rotationally symmetric working zone with one or more instances of a first pattern and a second rotationally-symmetric working zone with one or more instances of a second pattern, where at least one of the first pattern or the second pattern is a Moiré pattern formed from a first grating structure with a first pitch along a measurement direction on a first sample layer and a second grating structure with a second pitch different than the first pitch along the measurement direction on a second sample layer. Centers of rotational symmetry of the first and second working zones may overlap by design when an overlay error between the first sample layer and the second layer is zero. A difference between the centers of rotational symmetry of the first and second working zones may indicate an overlay error between the first and second sample layers.