Multi-Site Optical Metrology for Semiconductor Stack Characterization
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Solution Overview
Problem
Current methods for characterizing the optical material properties of multi-layer semiconductor structures, such as those with BARC and photoresist layers, face challenges in accuracy due to high spectral coupling and require numerous measurements across multiple wafers, which are time-consuming and prone to errors, failing to account for material property changes during fabrication processes.
Innovation Solution
A method and system that utilize optical measurements from multiple sites on a single wafer, employing a theoretical model to fit measured data and extract common parameters, allowing for accurate characterization of multi-layer structures by optimizing global parameters through inverse regression fits and reducing the need for multiple wafers and specialized measurement processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple wafers with additive stack methodology are used to characterize material properties, then measurement accuracy is improved, but measurement time and process complexity increase significantly
Solution Approach 1:
The patent segments the measurement approach by creating multiple test sites on a single wafer, each with different stack compositions (e.g., substrate-only, substrate with first material, substrate with both materials). This allows simultaneous characterization of multiple material properties across different sites without requiring multiple separate wafers, thereby reducing measurement time while maintaining accuracy.
Solution Approach 2:
The patent merges multiple measurement objectives into a single wafer by incorporating various test sites with different stack configurations. By combining substrate-only sites, first-material sites, and dual-material sites on one wafer, the method enables parallel extraction of multiple material properties (n and k values for different wavelengths) in a single measurement process.
2Measurement precision
If multiple wafers are measured using additive stack methodology, then sufficient data for material property determination is obtained, but the process becomes error-prone due to carry-over errors between wafers
Solution Approach 1:
The patent segments the measurement data collection by creating distinct test sites on a single wafer, each representing a different material stack configuration. This segmentation allows independent analysis of each site's optical response without carry-over errors between separate wafer measurements, as each site can be measured and analyzed independently while sharing common reference structures.
Solution Approach 2:
The patent uses copies of the same substrate and common reference structures across different test sites on the same wafer. By measuring multiple test sites that share common references (substrate, first material layer), the method eliminates the need to repeat measurements across multiple wafers, thereby reducing errors associated with wafer-to-wafer variations and measurement carry-over.
3Device complexity
If a single wafer with multiple test sites is used, then measurement process complexity is reduced, but sufficient spectral data for all material layers may not be obtained due to high spectral coupling
Solution Approach 1:
The patent applies local quality by creating test sites with specific local stack configurations tailored to characterize particular material properties. Each test site is designed with a specific combination of materials and layers (e.g., substrate only, substrate with first material, substrate with both materials) to locally optimize the measurement of specific optical properties, thereby reducing spectral coupling effects through targeted site design.
Solution Approach 2:
The patent resolves the spectral coupling problem by adding a spatial dimension - creating multiple test sites on a single wafer with different stack compositions. This dimensional approach allows the system to differentiate between spectral responses of different materials by measuring them at different spatial locations with different stack configurations, thereby separating coupled spectral signals through spatial multiplexing.
4Device complexity
If analytical modeling is used to reduce the number of independent variables, then measurement requirements are reduced, but correlations between parameters remain significant
Solution Approach 1:
The patent addresses parameter correlation by creating test sites with locally optimized stack configurations that are sensitive to specific material properties. By designing sites with different material combinations and stack depths, the method creates locally distinct optical responses that can be differentiated through simultaneous fitting, thereby reducing the correlation between extracted parameters while maintaining reduced measurement requirements.
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 precise characterization of optical material properties with high confidence levels, accounting for changes during fabrication, and reduces the complexity and cost of measurement processes by using a single wafer with multiple test sites, thereby improving process control and efficiency.
Implementation Method 1
Reflectometry based tools typically measure changes in the magnitude of radiation reflected/transmitted from/through the sample
Implementation Method 2
ellipsometry based tools typically measure changes of the polarization state of radiation after interacting with the sample
Data Source
AI summary
A method and system are presented for use in characterizing properties of an article having a structure comprising a multiplicity of sites comprising different periodic patterns, where method includes providing a theoretical model of prediction indicative of optical properties of different stacks defined by geometrical and material parameters of corresponding sites, said sites being common in at least one of geometrical parameter and material parameter; performing optical measurements on at least two different stacks of the article and generating optical measured data indicative of the geometrical parameters and material composition parameters for each of the measured stacks; processing the optical measured data, said processing comprising simultaneously fitting said optical measured data for the multiple measured stacks with said theoretical model and extracting said at least one common parameter, thereby enabling to characterize the properties of the multi-layer structure within the single article.