Representative Sensitivity Coefficient for Overlay Metrology
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Solution Overview
Problem
Conventional overlay metrology techniques face challenges in achieving accurate measurements due to varying sensitivity coefficients caused by physical imperfections in targets, leading to inconsistent results across different targets.
Innovation Solution
A method is developed to determine a representative sensitivity coefficient for a plurality of targets, using intensity asymmetry measurements and illumination characteristics, which allows for improved overlay metrology by accounting for target-specific imperfections and variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional overlay metrology techniques are used with a single sensitivity coefficient, then the measurement process is simple, but measurement precision deteriorates due to varying sensitivity coefficients caused by target imperfections
Solution Approach 1:
The patent divides the single sensitivity coefficient into multiple target-specific sensitivity coefficients, each determined from intensity asymmetry measurements of individual targets. This segmentation allows each target's unique structural characteristics to be accounted for, improving measurement precision while managing complexity through systematic processing of multiple coefficients.
Solution Approach 2:
The patent changes the sensitivity coefficient parameter from a single fixed value to multiple variable values specific to each target. By determining sensitivity coefficients individually for each target based on its intensity asymmetry measurements, the system adapts to target-specific variations, thereby improving overlay measurement accuracy despite increased process complexity.
2Measurement precision
If target-specific sensitivity coefficients are determined for each target, then measurement precision improves, but the complexity of determining and managing multiple coefficients increases
Solution Approach 1:
The patent implements a self-service mechanism where each target's sensitivity coefficient is automatically determined from its own intensity asymmetry measurements. The system uses the target's inherent structural information (captured in the intensity asymmetry) to generate its specific sensitivity coefficient, eliminating the need for manual calibration and reducing the complexity of managing multiple coefficients through automated, target-driven determination.
3Measurement precision
If intensity asymmetry measurements are used to determine sensitivity coefficients, then overlay measurement accuracy improves, but the measurement time and process complexity increase
Solution Approach 1:
The patent performs preliminary determination of sensitivity coefficients from intensity asymmetry measurements before conducting the actual overlay measurement. By pre-calculating the target-specific sensitivity coefficients and storing them for subsequent use, the system avoids repeated calculations during overlay measurements, thereby improving accuracy while minimizing the time loss associated with coefficient determination.
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 accuracy of overlay measurements by using a representative sensitivity coefficient, reducing the impact of target-specific structural asymmetries and improving the reliability of overlay calculations across multiple targets.
Implementation Method 1
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation
Implementation Method 2
Diffraction-based overlay using dark-field detection of the diffraction orders enables overlay measurements on smaller targets
Data Source
AI summary
Disclosed is a method of, and associated metrology apparatus for, determining a characteristic of a target on a substrate. The method comprises obtaining a plurality of intensity asymmetry measurements, each intensity asymmetry measurement relating to a target formed on the substrate and determining a sensitivity coefficient corresponding to each target, from the plurality of intensity asymmetry measurements. Using these sensitivity coefficients a representative sensitivity coefficient is determined for said plurality of targets or a subset greater than one thereof. The characteristic of the target can then be determined using the representative sensitivity coefficient.