Distance Measurement via Phase Image Correlation
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Solution Overview
Problem
Current methods for determining the distance between structure elements on substrates, such as masks, face limitations in measurement accuracy due to low signal-to-noise ratio and the non-comparability of aerial and phase images, which hinders precise localization and registration of structure features.
Innovation Solution
A method involving the recording of multiple images under varying conditions, with ensemble correlation functions being calculated from cross-correlation functions of pairs of images, enhancing signal-to-noise ratio and allowing for accurate distance determination between structure elements by averaging out noise and summing actual measurement signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple aerial images are recorded and averaged to increase measurement accuracy, then the signal-to-noise ratio improves slightly, but the improvement is minimal and does not significantly enhance measurement precision
Solution Approach 1:
The patent transforms aerial images into phase images by changing the parameter representation from intensity/amplitude to phase. This transformation fundamentally alters how measurement information is encoded, enabling much higher measurement precision through phase correlation rather than simple aerial image averaging.
Solution Approach 2:
The patent introduces phase images as an intermediary representation between the aerial images and the final measurement. By converting aerial images to phase images and using phase correlation as the intermediary measurement method, the system achieves superior signal-to-noise ratio and measurement accuracy compared to direct aerial image averaging.
2Measurement precision
If aerial images and phase images are averaged together to improve measurement accuracy, then more measurement information is utilized, but the images are not directly comparable making averaging meaningless
Solution Approach 1:
The patent applies parameter transformation by converting all aerial images to phase images using a consistent mathematical transformation. This ensures that all images are in the same parameter space (phase domain) and are directly comparable, resolving the incompatibility issue between aerial and phase images while enabling meaningful averaging and correlation operations.
3Device complexity
If simple microscopes are used for measurement, then device complexity is reduced, but measurement accuracy and reliability are compromised due to low signal-to-noise ratio
Solution Approach 1:
The patent replaces complex mechanical/optical measurement systems with a computational approach. By using phase image correlation and transformation methods, the system achieves high measurement precision through software-based processing rather than relying on complex hardware, allowing simple microscopes to deliver accurate measurements through intelligent image processing.
Data Source
AI summary
Provision is made of a method for determining a distance between a first structure element on a substrate and a second structure element, comprising the following steps: providing a first series of first images, wherein each of the first images comprises at least the first structure element, providing a second series of second images, wherein each of the second images comprises at least the second structure element. The method includes, for each image of the first and second series: determining a respective correlation function from a respective first image of the first series and a respective second image of the second series. The method includes determining an ensemble correlation function from the correlation functions, and determining the distance from the ensemble correlation function.Furthermore, a microscope for carrying out the method is provided.