Dynamic Sampling Scheme for Lithographic Overlay Metrology
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Solution Overview
Problem
Current overlay metrology methods in lithographic processes are inefficient, requiring costly dense measurements for each product and layer combination, and fail to adapt to changes in measurement actions or apparatus upgrades.
Innovation Solution
A method to determine a sampling scheme for overlay metrology based on the correlation between measurement actions on the measurement station and exposed portions of the substrate, allowing for dynamic adjustment of measurement density based on expected variability and minimizing the impact of measure-to-expose crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dense measurements are performed for each product and layer combination, then measurement precision is improved, but cost and measurement time increase
Solution Approach 1:
The patent implements dynamic sampling schemes that adapt measurement density based on real-time process conditions, product types, and layer characteristics. The system transitions from static dense measurements to dynamic adaptive measurements, adjusting the number and location of measurements based on expected variability and correlation data, thereby reducing measurement time while maintaining precision where needed
Solution Approach 2:
The system changes measurement parameters (sampling density, target selection, measurement locations) based on process conditions, product characteristics, and layer properties. By dynamically adjusting these parameters rather than using fixed dense sampling, the system achieves adequate measurement precision with reduced measurement time and cost
2Measurement precision
If dense measurements are performed for each product and layer combination, then measurement precision is improved, but cost increases
Solution Approach 1:
The system dynamically adjusts measurement parameters including sampling density and target selection based on process conditions and product characteristics. This adaptive approach reduces the number of measurements required while maintaining adequate precision, thereby reducing the cost associated with measurement resources
Solution Approach 2:
The patent implements adaptive sampling schemes that transition from static dense measurements to dynamic measurements adjusted according to expected variability and process conditions. This reduces the quantity of measurements performed, thereby reducing measurement costs while maintaining measurement quality where needed
3Ease of operation
If fixed sampling schemes are used, then ease of operation is improved, but adaptability to changes in measurement actions or apparatus upgrades deteriorates
Solution Approach 1:
The system implements dynamic sampling schemes that automatically adapt to changes in measurement actions, apparatus configurations, and process conditions. The sampling scheme is no longer fixed but dynamically adjusted based on real-time data about measurement variability and process conditions, providing both ease of operation through automation and adaptability to changes
Solution Approach 2:
The system uses feedback from measurement data, process conditions, and apparatus status to continuously adjust the sampling scheme. This feedback mechanism enables the system to adapt to changes in measurement actions or apparatus upgrades while maintaining ease of operation through automated adjustment rather than manual reconfiguration
4Measurement precision
If measurement actions are performed frequently, then measurement precision is improved, but overlay variation increases due to measure-to-expose crosstalk
Solution Approach 1:
The patent applies different measurement densities to different regions and contexts based on expected variability and process conditions. Rather than uniformly frequent measurements across all substrates and layers, the system performs measurements locally where needed based on adaptive sampling criteria, reducing measure-to-expose crosstalk while maintaining measurement precision where variability is higher
Solution Approach 2:
The system dynamically adjusts measurement frequency and density based on real-time assessment of expected variability and process conditions. This dynamic approach reduces unnecessary frequent measurements that cause crosstalk while maintaining adequate measurement precision in areas where variability requires closer monitoring
Data Source
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AI summary
Disclosed is a method of determining a sampling scheme for measuring at least one substrate or a portion thereof, the substrate being subject to a lithographic process to expose structures thereon using a lithographic apparatus comprising a measurement station for measuring the substrate and an exposure station for performing exposures on the substrate. The method comprises determining a correlation between measurement actions on said measurement station and exposed portions of said at least one substrate; determining an expected variability of a parameter of interest related to the lithographic process from said correlation; and determining the sampling scheme from said expected variability.