Hierarchical Sub-Shape Fitting for Lithography Overlay Precision
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Solution Overview
Problem
Current metrology techniques face limitations in reducing the size of metrology targets and improving measurement accuracy and sensitivity, particularly in overlay measurement, where existing methods struggle to capture diffraction orders effectively and separate target signals from surroundings, leading to less reliable results.
Innovation Solution
The method involves fitting sub-shapes of different orders hierarchically to describe a shape, using a computer system to optimize the fit of sub-shapes of the first and second order, and co-optimizing them to improve the accuracy of parameter determination, such as critical dimension and overlay error, by covering the area or volume of the shape while minimizing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional metrology techniques are used to measure overlay and critical dimension, then measurement can be performed, but measurement precision and sensitivity are insufficient, especially for small target sizes
Solution Approach 1:
The patent segments the metrology target into multiple diffraction order regions (first order, second order, etc.) that can be independently analyzed. Each diffraction order provides separate measurement information, allowing the target to be divided into functional zones that improve measurement precision without requiring a larger overall target area.
Solution Approach 2:
The patent transitions from analyzing only the zeroth diffraction order to utilizing multiple diffraction orders (first, second, and higher orders) in the angular spectrum domain. This dimensional expansion in the diffraction space enables enhanced measurement sensitivity and precision while maintaining compact target dimensions.
2Reliability
If conventional diffraction analysis is used, then target measurement is possible, but target signals cannot be effectively separated from surroundings
Solution Approach 1:
The patent segments the angular spectrum into distinct diffraction order regions, where each order is spatially separated and can be independently analyzed. This segmentation allows the target signal to be isolated from background and surrounding signals, improving reliability by preventing signal contamination.
Solution Approach 2:
The patent introduces diffraction order separation as an intermediary mechanism that acts as a spatial filter between the target signal and surrounding background. By utilizing the angular dispersion of diffraction, the method creates natural separation zones that prevent signal mixing and improve measurement reliability.
3Measurement precision
If single diffraction order analysis is used, then measurement is simpler, but measurement sensitivity and accuracy are reduced
Solution Approach 1:
The patent extends the analysis from a single diffraction order to multiple diffraction orders in the angular spectrum. This dimensional expansion provides additional measurement data points and enhances sensitivity, as each diffraction order contributes independent information about the target structure.
Solution Approach 2:
The patent combines measurements from multiple diffraction orders (zeroth, first, second, and higher orders) to achieve enhanced measurement precision. By merging the information from different diffraction regions, the method achieves superior accuracy while managing complexity through systematic data integration.
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 measurement sensitivity and accuracy, allowing for better decoupling of parameters and more precise determination of features, even at smaller target sizes, improving the reliability of overlay and critical dimension measurements.
Implementation Method 1
a scatterometer in which a beam of radiation is directed onto a target on a substrate and properties of the scattered and/or reflected (or more generally redirected) beam are measured
Implementation Method 2
properties of the scattered and/or reflected (or more generally redirected) beam are measured
Implementation Method 3
A spectroscopic scatterometer directs a broadband radiation beam onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation redirected into a particular narrow angular range
Implementation Method 4
An angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the redirected radiation as a function of angle
Data Source
AI summary
This disclosure includes a variety of methods of describing a shape in a hierarchical manner, and uses of such a hierarchical description. In particular, this disclosure includes a method comprising: fitting one or more sub-shapes of a first order against a shape; determining an error of the fitting; and fitting one or more sub-shapes of a second order against the error.