Lithography Focus Metrology with Single-Structure Signal Extraction
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Solution Overview
Problem
Current focus measurement procedures in lithographic apparatuses are time-consuming due to the need for lengthy focus testing procedures using multiple marks and complex signal processing, which are sensitive to overlay errors and noise, reducing throughput.
Innovation Solution
A method for determining focus using a single periodic structure per measurement location, decomposing the measurement data to extract processed component data with reduced dependence on non-focus related effects, and utilizing trained models to infer focus from the measurement data, along with a novel mark design that enhances focus sensitivity through alternating segments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional focus measurement procedures using multiple marks and complex signal processing are used, then measurement accuracy can be maintained, but measurement time increases significantly
Solution Approach 1:
The patent extracts and isolates the focus-dependent signal component from the measurement data by decomposing it into separate components. This allows the focus measurement to be determined from a single periodic structure by separating the focus-related signal from overlay errors and noise, achieving both speed and accuracy.
Solution Approach 2:
The patent changes the parameter being measured from position (traditional alignment sensor output) to focus by analyzing the amplitude or intensity of the periodic signal. This parameter transformation enables focus determination from a single structure without requiring multiple marks or complex processing.
2Measurement precision
If traditional alignment sensor methods are used, then overlay errors can be measured, but focus measurement becomes sensitive to overlay errors and noise
Solution Approach 1:
The patent extracts the focus-dependent component from the measurement data by decomposing the signal into focus-related and overlay-related components. This separation removes the harmful influence of overlay errors on focus measurement while maintaining measurement accuracy.
Solution Approach 2:
The measurement signal is segmented into distinct components: focus-dependent amplitude/intensity and overlay-dependent position. This segmentation allows independent analysis of focus without interference from overlay errors or noise.
Data Source
AI summary
Disclosed is a method for determining a focus parameter value used to expose at least one structure on a substrate. The method comprises obtaining measurement data relating to a measurement of said at least one structure, wherein the at least one structure comprises a single periodic structure per measurement location and decomposing said measurement data into component data comprising one or more components of said measurement data. At least one of said components is processed to extract processed component data having a reduced dependence on non-focus related effects and a value for the focus parameter is determined from said processed component data. Associated apparatuses and patterning devices are also disclosed.