Photomask Defect Inspection Using Reference Image Alignment
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Solution Overview
Problem
As microchips become more integrated and photomask patterns shrink, design rule checking times increase, leading to inefficiencies in defect detection due to misalignment issues during die-to-die image comparisons, which can result in rejecting good dies and masks as defective.
Innovation Solution
A defect inspecting apparatus generates reference images from design layout data and extracts coordinate offsets to align inspection images, allowing for accurate die-to-die comparisons and reducing alignment errors, thereby improving manufacturing yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photomask patterns are reduced in size to increase microchip integration, then manufacturing precision is improved, but measurement precision deteriorates due to alignment errors in die-to-die comparisons
Solution Approach 1:
The patent introduces a reference image as an intermediary element to facilitate accurate alignment between inspection images. The reference image, generated from design layout data, serves as a common reference frame that enables precise coordinate transformation and alignment between multiple inspection images, thereby resolving the alignment accuracy problem when inspecting reduced-size photomask patterns
Solution Approach 2:
The patent creates a reference image that is a copy of the design layout data in image form. This reference image copy is then used for comparison and alignment with actual inspection images, enabling accurate measurement and defect detection even when the original photomask patterns are reduced in size
2Manufacturing precision
If design rule checking is performed on highly integrated microchips with smaller patterns, then manufacturing precision is improved, but loss of time increases due to extended checking duration
Solution Approach 1:
The patent performs preliminary actions by generating reference images from design layout data before conducting the actual inspection. This pre-processing step establishes the reference framework in advance, enabling faster and more efficient die-to-die comparison during the inspection phase, thereby reducing the overall checking time for highly integrated microchips
3Productivity
If die-to-die image comparison is performed without coordinate alignment, then productivity is improved by simplifying the inspection process, but measurement precision deteriorates due to misalignment causing false defect detection
Solution Approach 1:
The patent replaces complex mechanical alignment procedures with computational image processing methods. By using reference images and coordinate transformation algorithms, the system achieves precise alignment automatically through software-based coordinate extraction and transformation, eliminating the need for manual or mechanical alignment while maintaining high measurement precision
Data Source
AI summary
A defect inspecting apparatus includes a reference image generator configured to generate a first reference image and a second reference image from design layout data. An image inspector is configured to obtain a first inspection image of a first inspection region of a photomask and a second inspection image of a second inspection region of the photomask. An operation processor is configured to extract a first coordinate offset by comparing the first inspection image with the first reference image and to extract a second coordinate offset by comparing the second inspection image with the second reference image.