Diffraction Signal Weighting for Noise-Robust Optical Metrology
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Solution Overview
Problem
Weak measured diffraction signals in optical metrology due to noise from hardware and the feature being measured reduce the accuracy of the optical metrology process.
Innovation Solution
A weighting function is defined based on noise, accuracy, and sensitivity of the measured diffraction signal to enhance the signal quality, which is achieved by generating noise and error profiles, and using multivariate analysis to transform the signals, ultimately combining these to produce an enhanced diffraction signal for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a measured diffraction signal is obtained using a photometric device, then the optical metrology process can determine wafer feature characteristics, but the measured signal is weak and contains noise which decreases measurement accuracy
Solution Approach 1:
The patent converts the harmful noise in the measured diffraction signal into a useful component by creating a weighting function that incorporates noise characteristics. The noise profile, which was previously degrading measurement accuracy, is now used to define weights that enhance the signal-to-noise ratio in the enhanced diffraction signal, turning the harmful noise into a beneficial element for improving measurement precision
Solution Approach 2:
The patent applies parameter changes by transforming the measured diffraction signal through a weighting function that modifies the signal's characteristics. The weighting function adjusts parameters such as signal intensity and noise distribution across different spatial frequencies, creating an enhanced diffraction signal with improved signal-to-noise ratio and measurement accuracy
2Measurement precision
If the measured diffraction signal is enhanced using a weighting function, then the accuracy and sensitivity of optical metrology improve, but the complexity of the measurement process increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing a weighting function based on noise profiles and sensitivity characteristics before actual measurements are performed. This pre-computed weighting function is then applied to enhance measured diffraction signals, avoiding the need for complex real-time calculations during measurement and reducing processing complexity while maintaining improved accuracy
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
The weighting function enhances the accuracy of the optical metrology process by reducing noise and improving signal uniformity, leading to more precise characterization of features on semiconductor wafers.
Implementation Method 1
a measured diffraction signal is obtained from a feature to be examined... using a photometric device
Implementation Method 2
Periodic grating 102 is illuminated by an incident beam 108... Diffracted beam 110 leaves
Data Source
AI summary
A weighting function is obtained to enhance measured diffraction signals used in optical metrology. To obtain the weighting function, a measured diffraction signal is obtained. The measured diffraction signal was measured from a site on a wafer using a photometric device. A first weighting function is defined based on noise that exists in the measured diffraction signal. A second weighting function is defined based on accuracy of the measured diffraction signal. A third weighting function is defined based on sensitivity of the measured diffraction signal. A fourth weighting function is defined based on one or more of the first, second, and third weighting functions.