Lithographic Metrology Using Unsupervised Cluster Analysis
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Solution Overview
Problem
Current metrology methods in lithographic processes are inefficient for quickly determining the shape and properties of scatterometry targets, requiring extensive time and specialized equipment, and struggle to choose robust nominal values for parameter reconstruction.
Innovation Solution
A method involving unsupervised cluster analysis of inspection data to partition it into clusters, allowing for more informed selection of target structures that represent average values, thereby simplifying the reconstruction of target shapes and properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cross-section scanning electron microscope is used to determine the shape of scatterometry target, then measurement accuracy is improved, but measurement time and device complexity increase significantly
Solution Approach 1:
The patent uses scatterometry to create an indirect optical copy of the target structure by analyzing diffraction patterns, replacing the need for direct physical imaging with scanning electron microscope. This copying approach maintains measurement accuracy while dramatically reducing measurement time and device complexity
Solution Approach 2:
The patent replaces the mechanical scanning electron microscope system with an optical scatterometry system that uses light diffraction patterns to determine target shape. This substitution eliminates the need for complex mechanical scanning and sample preparation while achieving comparable measurement accuracy
2Measurement precision
If cross-section scanning electron microscope is used to determine the shape of scatterometry target, then measurement accuracy is improved, but device complexity and resource requirements increase
Solution Approach 1:
The patent makes the lithographic apparatus itself perform metrology functions by integrating scatterometry capability into the existing system. The same optical infrastructure used for lithography is leveraged for target shape measurement, eliminating the need for separate specialized scanning electron microscope equipment
Solution Approach 2:
The patent creates an indirect optical representation of the target structure through diffraction pattern analysis, replacing the need for complex physical imaging equipment. This copying method achieves accurate shape determination using simpler, more integrated apparatus
3Measurement precision
If traditional reconstruction methods are used without clustering, then complete inspection data is analyzed, but processing time and computational resources increase
Solution Approach 1:
The patent segments the complete inspection data set into multiple clusters based on similarity metrics. By dividing the data into manageable clusters and selecting representative targets from each, the system maintains comprehensive analysis accuracy while dramatically reducing computational processing time and resource requirements
4Ease of operation
If random target selection is used for reconstruction, then simplicity is maintained, but measurement accuracy and robustness decrease
Solution Approach 1:
The patent performs preliminary clustering analysis to identify representative targets before the actual reconstruction process. This preliminary action groups similar targets and selects optimal representatives, ensuring high measurement accuracy while maintaining operational simplicity through automated selection criteria
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 significantly reduces the time and resources needed for metrology measurements, improving the efficiency and accuracy of lithographic process control by identifying cluster representatives that best represent average parameter values.
Implementation Method 1
In order that the radiation that impinges on to the substrate is diffracted, an object with a specific shape is printed on to the substrate and is often known as a scatterometry target or simply target
Implementation Method 2
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation
Data Source
AI summary
Disclosed are a method, computer program and associated apparatuses for metrology. The method includes acquiring inspection data comprising a plurality of inspection data elements, each inspection data element having been obtained by inspection of a corresponding target structure formed using a lithographic process; and performing an unsupervised cluster analysis on said inspection data, thereby partitioning said inspection data into a plurality of clusters in accordance with a metric. In an embodiment, a cluster representative can be identified for each cluster. The cluster representative may be reconstructed and the reconstruction used to approximate the other members of the cluster.