Lithographic Spectral Analysis Using Precomputed Calibration Libraries
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Solution Overview
Problem
Current methods for determining process parameters in lithographic processes are inefficient, requiring numerous calculations to achieve accurate matches between measured and calculated spectra, leading to a compromise between accuracy and processing speed.
Innovation Solution
A method involving the calculation of calibration spectra using different known structure parameters, followed by spectral analysis to obtain common spectral components and weighting factors, which are then used to compare and derive the structure parameters of a target pattern, reducing the number of necessary calculations through the use of principal component analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If iterative search methods are used to find the best match between measured and calculated spectra, then measurement precision is improved, but processing time increases significantly
Solution Approach 1:
The patent applies preliminary action by pre-calculating a comprehensive library of spectra for all possible structure parameter combinations before actual measurement. This pre-computed library stores the relationship between structure parameters and spectral characteristics, eliminating the need for time-consuming iterative calculations during real-time inspection. When a measurement is taken, the system simply compares the measured spectrum against the pre-existing library to quickly identify the best match, thus resolving the contradiction between precision and processing time.
Solution Approach 2:
The patent creates a copy of the spectral data in the form of a pre-computed library that replicates the relationship between structure parameters and spectral characteristics. Instead of performing repeated calculations on the actual measured data, the system uses this copied reference library for rapid comparison and identification, significantly reducing processing time while maintaining measurement accuracy.
2Measurement precision
If comprehensive spectral analysis is performed on all data points, then measurement precision is improved, but computational complexity increases
Solution Approach 1:
The patent extracts only the essential spectral information needed for accurate structure parameter determination by comparing measured spectra against the pre-computed library. Instead of performing complex iterative analysis on all spectral data points, the system extracts the key matching characteristics from the library comparison, reducing computational complexity while preserving measurement precision.
3Manufacturing precision
If iterative search techniques are used to achieve best match, then manufacturing precision is improved, but productivity decreases
Solution Approach 1:
By pre-calculating and storing the comprehensive spectrum library before production runs, the system enables rapid inspection during manufacturing without sacrificing precision. The pre-computed library allows operators to quickly determine process parameters by simple comparison rather than iterative search, thereby maintaining manufacturing precision while significantly improving inspection throughput and overall productivity.
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 allows for more efficient calculation of spectra without reducing accuracy, enabling faster and more precise determination of structure parameters in lithographic processes.
Implementation Method 1
a beam of radiation is directed onto a target on the surface of the substrate and one or more properties of the scattered or reflected beam are measured
Implementation Method 2
one or more properties of the scattered or reflected beam are measured
Data Source
AI summary
In a method of determining a structure parameter of a target pattern in a lithographic process, a series of calibration spectra are calculated from a reference pattern. Spectral analysis is performed on each calculated spectra, the spectral components and associated weighting being derived and stored in a library or used as the basis of an iterative search method. A spectrum is measured from the target pattern and spectral analysis of the measured spectrum is performed. The derived weighting factors of the principal components are compared with the weighting factors of the measured spectrum to determine the structure parameter.