Polarization Filtering for Lithography Overlay Measurement Accuracy
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Solution Overview
Problem
Current metrology techniques in lithographic processes rely heavily on measuring asymmetry signals, which are often influenced by unknown process variables, leading to reduced accuracy in determining parameters of interest such as overlay, focus, and dose.
Innovation Solution
An inspection apparatus and method utilizing an optical system with a two-stage filtering technique, where an illumination beam is polarized with a first polarization and scattered radiation is analyzed for orthogonal polarization, allowing for the determination of parameters of interest by isolating asymmetric components through a combination of first and second filter components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If asymmetry signals are used for measurement, then overlay, focus, and dose parameters can be determined, but measurement accuracy is reduced due to influence from unknown process variables
Solution Approach 1:
The patent segments the measurement signal into symmetric and asymmetric components using polarization filtering. By separating the asymmetric component (which contains overlay, focus, and dose information) from the symmetric component (influenced by process variables), the measurement accuracy is improved while eliminating the harmful influence of process variable variations.
Solution Approach 2:
The patent extracts the asymmetric component of the scattered radiation signal using orthogonal polarization filtering. This extraction isolates the parameter-of-interest information (overlay, focus, dose) from the symmetric background signals that are contaminated by unknown process variables, thereby improving measurement reliability.
2Measurement precision
If conventional scatterometry is used, then diffraction spectrum can be obtained, but measurement accuracy is compromised due to interference from product structures
Solution Approach 1:
The patent exploits the asymmetric scattering pattern generated by overlay targets compared to symmetric product structures. By using orthogonal polarization filtering to isolate asymmetric components, the measurement system can distinguish overlay target signals from the symmetric background of product structures, eliminating interference and improving measurement accuracy.
Solution Approach 2:
The patent converts the normally harmful effect of product structure interference into a beneficial filtering mechanism. By utilizing the symmetry difference between product structures and overlay targets, the orthogonal polarization filter transforms the background interference into a reference signal that helps isolate and enhance the asymmetric overlay target signal.
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 accuracy by isolating asymmetric components associated with parameters of interest, improving the precision of overlay, focus, and dose measurements in lithographic processes.
Implementation Method 1
applying a first polarization to the illumination beam using a first filter component
Implementation Method 2
applying a second polarization to at least a portion of the illumination beam that scatters off the one or more features using a second filter component, wherein the second filter component is located orthogonal to the first filter component
Implementation Method 3
at least a portion of the illumination beam scattered by the one or more features
Data Source
AI summary
An inspection apparatus, method, and system are described herein. An example inspection apparatus includes an optical system and an imaging system. The optical system may be configured to output an illumination beam incident on a target including one or more features, the illumination beam polarized with a first polarization when incident on the target. The imaging system may be configured to obtain intensity data representing at least a portion of the illumination beam scattered by the one or more features, where the portion of the illumination beam has a second polarization orthogonal to the first polarization. The inspection apparatus may be further configured to generate image data representing an image of each of the feature(s) based on the intensity data, and determine a measurement of a parameter of interest associated with the feature(s) based on an amount of the portion of the illumination beam having the second polarization.