Metrology Reconstruction Error Detection Using Sensitivity Maps
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Solution Overview
Problem
Current reconstruction techniques in metrology are mathematically and computationally complex due to the numerous permutations of parameters that need to be varied, making them inefficient for overlay metrology.
Innovation Solution
A method is introduced that involves obtaining model parameters for a nominal profile, metrology data, and simulated data to determine a spatially resolved sensitivity metric. This metric describes the sensitivity of a cost function to properties and functions of the structure, allowing for the identification of the source of reconstruction errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional reconstruction techniques are used to measure structure parameters, then measurement precision can be achieved, but computational complexity and processing time increase significantly
Solution Approach 1:
The patent segments the complex reconstruction problem into distinct measurement modes (reflection mode and transmission mode) with different mathematical approaches. Each mode uses a simplified reconstruction algorithm tailored to its specific measurement geometry, avoiding the need to solve the full complex reconstruction problem for all cases.
Solution Approach 2:
The patent changes the measurement parameters by using different illumination geometries (reflection vs transmission) and selecting appropriate reconstruction algorithms for each. This allows the system to achieve accurate measurements while reducing computational complexity by matching the measurement configuration to the simplest suitable reconstruction method.
2Measurement precision
If multiple parameters are varied in reconstruction techniques, then measurement accuracy improves, but processing time increases
Solution Approach 1:
The patent performs preliminary classification of the measurement problem into reflection mode or transmission mode before executing the reconstruction algorithm. This preliminary action allows the system to select the appropriate simplified algorithm in advance, avoiding unnecessary computational steps and reducing processing time while maintaining measurement accuracy.
3Measurement precision
If dedicated metrology targets are used for scatterometry measurements, then measurement precision improves, but the method becomes less adaptable to different measurement scenarios
Solution Approach 1:
The patent creates a universal measurement method that works for both reflection mode and transmission mode scatterometry measurements. The same basic apparatus and methodology can be applied to different measurement scenarios by simply changing the illumination geometry and selecting the appropriate reconstruction algorithm, making the method highly adaptable while maintaining precision.
Data Source
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AI summary
Disclosed is a method of identifying a source of a reconstruction error relating to reconstruction of a plurality of model parameters describing a structure on a substrate formed in a lithographic process. The method comprises: obtaining model parameters describing a nominal profile for describing said structure; obtaining metrology data relating to a measurement of said structure; determining simulated data, from a simulation of the measurement of said structure described in accordance with said model parameters; determining a spatially resolved sensitivity metric describing a sensitivity of a cost function to at least one property and/or function of said structure, said cost function comparing the metrology data and simulated data; and identifying a source of a reconstruction error from said spatially resolved sensitivity metric.