Optical Metrology Model Parameter Optimization
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Solution Overview
Problem
Conventional optical metrology systems for semiconductor wafers are time-consuming and costly due to the complex calculations required for generating simulated diffraction signals using rigorous coupled wave analysis, which limits their efficiency in determining the profile of patterned structures.
Innovation Solution
An optical metrology model is created with defined ranges of profile, material refraction, and metrology device parameters, optimized using measured diffraction signals, where at least one parameter is set to a fixed value within these ranges, allowing for the determination of profile parameters through iterative comparison and refinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rigorous coupled wave analysis (RCWA) is used to generate simulated diffraction signals, then measurement precision is improved, but productivity deteriorates due to time-consuming calculations
Solution Approach 1:
The patent pre-calculates and stores diffraction signals for various profile parameters in a lookup table before actual measurement. When a real diffraction signal is obtained, the system quickly searches the pre-computed table for matching signals rather than performing complex RCWA calculations in real-time, thus achieving fast profile determination without sacrificing measurement precision
Solution Approach 2:
The patent creates simplified copy models that represent the complex physical structures in a computationally efficient manner. These copy models capture the essential optical characteristics needed for profile determination while requiring significantly less computational resources than full RCWA simulations, enabling rapid analysis while maintaining acceptable accuracy
2Measurement precision
If extensive libraries of simulated diffraction signals are generated using RCWA, then measurement precision is improved, but loss of time increases due to the large number of complex calculations
Solution Approach 1:
The system performs the computationally intensive library generation in advance and stores the results. During actual measurement operations, only simple lookup and comparison operations are needed, transforming a time-consuming calculation process into a fast retrieval process, thereby eliminating the time loss during critical measurement phases
Solution Approach 2:
The patent implements a dynamic approach where the system adapts its processing strategy based on the specific measurement context. For routine measurements, it uses the pre-computed lookup table for rapid results. When higher precision is needed or new profile types are encountered, it can selectively perform additional RCWA calculations only for the necessary parameter ranges, optimizing the balance between precision and time investment
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 reduces the computational burden and enhances the efficiency of determining profile parameters, enabling real-time profile estimation and improving the accuracy of patterned structure analysis without relying on extensive libraries of simulated diffraction signals.
Implementation Method 1
The electromagnetic radiation that deflects off of the periodic grating are collected as a diffraction signal
Data Source
AI summary
An optical metrology model is created for a patterned structure formed on a semiconductor wafer. The optical metrology model has profile parameters, material refraction parameters, and metrology device parameters. Ranges of values for the parameters are defined. One or more measured diffraction signals of the patterned structure are obtained. The optical metrology model is optimized to obtain an optimized optical metrology model using the defined ranges of values defined and the one or more obtained measured diffraction signals of the patterned structure. For at least one parameter from amongst the material refraction parameters and the metrology device parameters, the at least one parameter is set to a fixed value within the range of values for the at least one parameter. At least one profile parameter of the patterned structure is determined using the optimized optical metrology model and the fixed value for the at least one parameter.