Lithographic Metrology Parameter Reconstruction via Grid Transformation
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Solution Overview
Problem
Current reconstruction methods in lithographic metrology face challenges in accurately determining parameters of interest, such as critical dimension and overlay, due to differences in measurement grids and the need for extensive parameter fitting, which can lead to inefficiencies and inaccuracies in process control.
Innovation Solution
A method and apparatus that combine measured values of a first parameter to obtain an estimated value, which is then used to reconstruct at least a second parameter associated with the structure, utilizing a processor and detection system to analyze scattered radiation and optimize sampling schemes based on prior knowledge and statistical distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If prior knowledge from previously measured parameters is used in reconstruction, then the number of parameters to be resolved is reduced, but measurement inaccuracies from different measurement grids propagate to the parameter of interest
Solution Approach 1:
The patent applies preliminary action by measuring and storing parameters from previous layers before performing reconstruction of the current layer. The system pre-acquires overlay, focus, and other process parameters from prior measurements, then uses these pre-obtained values to reduce the number of parameters needing resolution during the actual reconstruction process, while the grid transformation method ensures accuracy is maintained.
2Adaptability or versatility
If measurements are taken at different locations on the substrate, then comprehensive process coverage is achieved, but correlation between previously measured parameters and current parameter of interest is reduced
Solution Approach 1:
The patent uses grid transformation as an intermediary mechanism to bridge measurements taken at different locations. The system transforms parameters from the measurement grid where they were originally acquired to the grid system of the current target, enabling accurate correlation even when measurements were taken at different substrate locations. This intermediary transformation maintains parameter correlation while preserving the benefits of comprehensive process coverage.
3Measurement precision
If extensive parameter fitting is performed during reconstruction, then accurate determination of parameters of interest is achieved, but processing time and computational resources increase
Solution Approach 1:
The patent extracts and removes parameters from the reconstruction process that can be obtained from previous measurements. By taking out parameters like overlay and focus that were already measured in prior layers and making them available through grid transformation, the system reduces the number of parameters requiring extensive fitting during reconstruction, thereby decreasing processing time while maintaining accuracy for the remaining parameters.
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 and efficiency of parameter reconstruction by reducing the number of parameters to be fitted and allowing for optimized sampling, thereby improving process control and throughput in lithographic processes.
Implementation Method 1
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation
Data Source
AI summary
A method of reconstructing a characteristic of a structure formed on a substrate by a lithographic process, and an associated metrology apparatus. The method includes combining measured values of a first parameter associated with the lithographic process to obtain an estimated value of the first parameter; and reconstructing at least a second parameter associated with the characteristic of the structure using the estimated value of the first parameter and a measurement of the structure. The combining may involve modeling a variation of the first parameter to obtain a parameter model or fingerprint of the first parameter.