Lithography Metrology Correction for Measurement Condition Variations
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Solution Overview
Problem
In lithographic processes, measuring microscopic structures on substrates is challenging due to variations in measurement conditions, which can lead to inaccuracies in reconstructing critical parameters like critical dimensions and overlay errors, especially for complex structures or those involving specific materials, as existing methods struggle to accurately compensate for differences in measurement conditions.
Innovation Solution
A method and apparatus that determine a correction to compensate for variations in measurement conditions by performing multiple measurements under different conditions and using a weighting matrix to suppress the influence of these variations, allowing for a more accurate reconstruction of the substrate's parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measurements are performed under different measurement conditions to improve accuracy, then measurement precision is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating weighting matrices for different measurement conditions before actual measurements are performed. These weighting matrices are stored and then applied during the reconstruction process to compensate for measurement condition variations, eliminating the need for real-time complex calculations and reducing measurement system complexity while maintaining high measurement precision.
Solution Approach 2:
The patent introduces weighting matrices as an intermediary element that mediates between multiple measurements under different conditions and the final parameter reconstruction. These weighting matrices act as compensatory factors that suppress the influence of measurement condition variations, allowing accurate reconstruction without requiring complex real-time processing of all measurement variations.
2Measurement precision
If multiple measurements are performed under different measurement conditions to improve accuracy, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs the computationally intensive calculation of weighting matrices in advance, before actual measurements are taken. These pre-calculated weighting matrices are then applied during the reconstruction phase, significantly reducing the time required during actual measurements while still achieving high precision by utilizing multiple measurements under different conditions.
3Measurement precision
If the number of floating parameters in the model is increased to accurately represent complex structures, then measurement precision is improved, but device complexity and computational load increase
Solution Approach 1:
The patent introduces weighting matrices as an intermediary that compensates for measurement condition variations, allowing the use of simpler models with fewer floating parameters while maintaining high reconstruction accuracy. The weighting matrices absorb the complexity of handling multiple measurement conditions, enabling accurate parameter reconstruction without requiring excessively complex models with numerous floating 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 robustness of parameter reconstruction by mitigating the effects of measurement condition variations, improving the precision of critical dimension and overlay error measurements, and reducing the risk of false matches in model reconstruction.
Implementation Method 1
an optical system for selectively illuminating said structure with radiation and collecting at scattered radiation which has been scattered by the structure
Data Source
AI summary
Disclosed is a method of measuring a parameter of interest relating to a structure on a substrate, and associated metrology apparatus. The method comprises determining a correction to compensate for the effect of a measurement condition on a measurement signal from a plurality of measurement signals, wherein each of said measurement signals results from a different measurement of the structure performed under a different variation of said measurement condition. The correction is then used in a reconstruction of a mathematical model of said structure to suppress an influence of variations of said measurement condition on the reconstruction.