Noise Correction for Alignment Signal in Metrology Systems
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Solution Overview
Problem
Current metrology systems in lithographic apparatuses face challenges in accurately aligning substrates due to insufficient noise correction strategies, leading to overlay mismatches as feature sizes on substrates become smaller.
Innovation Solution
A metrology system that includes a radiation source, reflector, interferometer, detector, and controller, which determines a correction by characterizing measurements in an orthogonal subspace, with axes corresponding to constructive and destructive interference outputs, and calculates a slope to fit a line to the data, effectively accounting for noise variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current noise correction strategies are used in metrology systems, then the system structure remains simple, but measurement precision deteriorates leading to overlay mismatches
Solution Approach 1:
The patent transforms the noise correction problem from a one-dimensional signal processing task into a two-dimensional geometric analysis by plotting measurements in an orthogonal subspace with constructive and destructive interference axes. This dimensional transformation enables more effective noise separation and correction, directly improving measurement precision without excessive complexity increase
Solution Approach 2:
The patent applies preliminary noise correction by determining a fitted line through the orthogonal subspace data before final alignment measurements are made. This preliminary establishment of the noise model allows subsequent measurements to be corrected more effectively, improving precision while maintaining manageable system complexity
2Productivity
If feature sizes on substrate are reduced to increase productivity, then manufacturing precision deteriorates due to insufficient alignment accuracy
Solution Approach 1:
The patent implements a feedback mechanism where noise correction is continuously applied based on the orthogonal subspace analysis. The fitted line determination and correction application create a closed-loop system that compensates for noise effects, maintaining manufacturing precision even as feature sizes are reduced to increase productivity
Solution Approach 2:
The patent changes the parameter space by transforming alignment measurements into an orthogonal subspace with specific error variable assignments. This parameter transformation enables more effective noise correction, allowing smaller features to be aligned with sufficient precision while maintaining high 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 improves the accuracy of substrate alignment by effectively correcting noise in the measurement data, reducing overlay mismatches and enhancing the precision of feature alignment on smaller substrate features.
Implementation Method 1
The interferometer interferes the light that has been diffracted from a pattern on the substrate, or reflected from the substrate, and produces output light from the interference
Implementation Method 2
The reflector directs at least a portion of the light towards the substrate
Data Source
AI summary
A method of applying a measurement correction includes determining an orthogonal subspace used to characterize the measurement as a plot of data. A first axis of the orthogonal subspace corresponds to constructive interference output from an interferometer of the metrology system plus a first error variable and a second axis of the orthogonal subspace corresponds to destructive interference output from the interferometer of the metrology system plus a second error variable. The method also includes determining a slope of the plot of data and determining a fitted line to the plot of data in the orthogonal subspace based on the slope.