Mask Holder Position Detection Using Reference Image Correlation
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Solution Overview
Problem
Conventional methods for calibrating and measuring the position of a mask holder in semiconductor lithography face significant measurement errors due to the roughness and irregularity of the holder edges, leading to reduced reproducibility and accuracy.
Innovation Solution
A method that involves recording and storing a reference image of the mask holder's edge profile, allowing for increased reproducibility by comparing subsequent measurement images to the reference using two-dimensional correlative image analysis, which accounts for the irregular structure of the holder edges and enables accurate determination of position and rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If straight lines are approximated to the edge profile of the mask holder, then the measurement process is simplified, but measurement errors increase due to the roughness and irregularity of the holder edges
Solution Approach 1:
The patent creates a digital copy of the actual irregular edge profile by recording a reference image during calibration. This reference image captures the true geometry of the holder edges including all roughness and irregularities. During subsequent measurements, this reference copy is used for correlation analysis instead of idealized straight lines, thereby preserving measurement accuracy while maintaining process simplicity.
2Adaptability or versatility
If different image portions are used for measuring the holder edges due to placement tolerances, then the measurement system remains flexible, but significant measurement errors arise
Solution Approach 1:
The patent implements a feedback mechanism where the reference image (captured during calibration) is stored and subsequently used to guide and correct measurements. During operation, the measured image portions are correlated with the reference image to determine the actual holder position and orientation. This feedback loop compensates for placement tolerances and ensures accurate measurements regardless of which image portions are captured.
3Productivity
If the mask holder is measured without accounting for edge irregularities, then the measurement process is faster, but reproducibility decreases
Solution Approach 1:
The patent performs preliminary action by capturing and storing a reference image of the holder edges during a calibration step before actual measurements begin. This reference image pre-characterizes the specific irregularities of the holder being measured. During subsequent rapid measurements, this pre-acquired reference information is used for correlation analysis, enabling both high speed and high reproducibility without needing to re-characterize the holder edges each time.
Data Source
AI summary
The invention relates to a method for detecting the position of a mask holder for photolithographic masks, said method including the following steps:positioning the mask holder with the mask on a measuring table of a measurement apparatus,measuring the mask holder by use of an algorithm,storing the absolute position of the mask holder on the measuring table, andrecording and storing at least one reference image.