Photomask Image Correlation Using Structural Edge Variations
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Solution Overview
Problem
Current methods for correlating images of photolithographic masks, especially in the EUV range, face challenges due to the need for precise alignment and the limitations of existing marker-based techniques, which are either inaccurate or labor-intensive, and often result in unwanted scanboxes or require additional processing steps.
Innovation Solution
An apparatus and method that utilize random variations in structural elements of the photomask as natural markers for image correlation, allowing for accurate alignment without the need for additional markers or processing steps, using particle microscopes and scanning probe microscopes to achieve high precision and efficient defect correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If markers are positioned blindly around the assumed defect location, then the two images can be precisely superimposed, but markers may be positioned at wrong locations and the photomask may be processed in a wrong location
Solution Approach 1:
The method uses the photomask's own structural elements (edges of lines and spaces) as correlation markers instead of adding external markers. The correlation unit automatically identifies and uses these pre-existing structural features to superimpose the SEM and AFM images, eliminating the need for blind marker positioning and ensuring accurate defect location through the mask's inherent structure
Solution Approach 2:
The method extracts and utilizes the random variations and edge structures that already exist in the photomask's structural elements. By focusing on these inherent features rather than adding external markers, the system achieves precise image correlation while maintaining reliability in defect location
2Measurement precision
If markers are applied to the photomask for image correlation, then the images can be superimposed, but additional processing steps are required and time is consumed
Solution Approach 1:
The photomask serves its own dual purpose: it is both the object to be inspected and the source of correlation markers. The structural elements of the mask itself provide the reference features needed for image superposition, eliminating the need for separate marker application and removal steps
Solution Approach 2:
The structural elements of the photomask serve multiple functions: they define the pattern to be manufactured and simultaneously serve as correlation markers for image superposition. This multi-functionality eliminates the need for dedicated marker features and reduces processing steps
3Ease of manufacture
If calibration markers are spaced apart on the mask, then they can be used for device calibration, but they are not shown in individual image sections and accuracy is limited
Solution Approach 1:
Instead of relying on sparsely distributed calibration markers, the method uses local structural features (edges of lines and spaces) that are present throughout the entire photomask surface. These local features are visible in every image section and provide continuous reference points for accurate image correlation at the defect location
Data Source
AI summary
An apparatus for correlating at least two images of a photolithographic mask that at least partially overlap, in which the apparatus includes a correlation unit that is provided to use at least one random variation, which is present in the at least two images, of at least one structural element of the photolithographic mask for the correlation of the at least two images.