Photolithographic Mask Position Determination Using Optimized Reference Images
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Solution Overview
Problem
Current methods for determining the position of structure elements on photolithographic masks face challenges in achieving high precision due to errors from optical aberrations, noise, and positioning defects, particularly in the sub-nanometer range, which complicates the repair and production of masks.
Innovation Solution
A method that involves optimizing a reference image by correcting defects and errors through metadata analysis, including positioning errors and optical system parameters, to improve the accuracy of position determination by correlating the optimized reference image with measured images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If evaluation methods measuring images in absolute terms are used, then absolute position specification is provided, but measurement results are falsified by optical apparatus properties
Solution Approach 1:
A reference image serves as an intermediary between the optical measurement system and the final position determination. The reference image is recorded under ideal conditions and used to compensate for optical aberrations, apodization, and other system-specific distortions when evaluating measured images, thereby eliminating the falsifying effect of apparatus properties while maintaining absolute position specification
Solution Approach 2:
The reference image is created in advance under optimized conditions before actual mask measurements are performed. This preliminary action captures the ideal optical response, which is then used to correct and compensate for system-specific distortions during subsequent measurements, improving both measurement precision and reliability
2Reliability
If die-to-database evaluation with model reference images is used, then independence from optical aberrations is achieved, but dependence on model function quality arises
Solution Approach 1:
Instead of using a theoretical model function, the patent creates an actual recorded reference image that copies the ideal optical response under known conditions. This empirical reference image retains independence from optical aberrations while providing higher precision because it reflects actual system behavior rather than theoretical assumptions
3Object-affected harmful factors
If die-to-die evaluation with measured reference images is used, then higher tolerance for poor signal-to-noise ratio is achieved, but position determination is only relative
Solution Approach 1:
The reference image acts as an intermediary that bridges relative and absolute measurement systems. By recording the reference image under ideal conditions and using it to evaluate measured images, the method achieves both the noise tolerance of relative evaluation and the absolute position determination capability, as the reference image itself contains absolute position information
Data Source
AI summary
The invention relates to a method and an apparatus for determining a position of at least one structure element of a photolithographic mask, wherein the method comprises the following steps: (a) providing a reference image of the at least one structure element; (b) deriving a data record for the reference image, said data record comprising metadata relating to the reference image; (c) providing at least one measured image of the at least one structure element of the photolithographic mask; and (d) optimizing the reference image by use of the derived data record and correlating the at least one measured image and the optimized reference image.