Photomask Image Inspection Using Equalized CD Deviation Values
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Solution Overview
Problem
Existing image inspection methods struggle to accurately detect critical dimension (CD) defects in photomasks due to variations in pattern dimensions caused by manufacturing processes, which can lead to increased inspection costs and reduced accuracy.
Innovation Solution
An image processing apparatus and method that utilize an optical system to acquire and process image data, correcting luminance variations and evaluating CD deviations through equalized evaluation values, enabling detection of defects and variations in pattern dimensions across multiple regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single apparatus performs multiple types of inspection, then inspection cost is reduced, but measurement precision for CD defects deteriorates due to manufacturing variations
Solution Approach 1:
The patent creates a reference image by copying and averaging patterns from multiple regions to establish a standard template. This reference image serves as a benchmark for detecting CD defects, allowing the system to distinguish between normal manufacturing variations and actual defects by comparing target images against the synthesized reference
Solution Approach 2:
The patent transforms the inspection approach by changing from direct absolute measurement to relative deviation measurement. By calculating the difference between target images and the reference image, the system converts manufacturing variations into a removable baseline, enabling precise defect detection despite using a single apparatus for multiple inspection types
2Productivity
If multiple inspection types are integrated into one apparatus, then inspection cost decreases, but device complexity increases
Solution Approach 1:
The patent implements a universal image processing flow that handles multiple inspection types (CD defect inspection, micro-defect inspection, pattern defect inspection) through a single apparatus. The system uses a common reference image creation and comparison mechanism that can be applied across different inspection modes, reducing the need for separate specialized equipment while maintaining inspection capabilities
3Speed
If CD inspection is performed based on images, then inspection speed increases, but measurement precision deteriorates due to luminance variations
Solution Approach 1:
The patent performs preliminary normalization of the reference image by averaging patterns from multiple regions before using it for defect detection. This pre-processing step establishes a stable baseline that compensates for luminance variations, allowing subsequent defect detection to proceed quickly without sacrificing measurement precision
Solution Approach 2:
The system creates a reference image by copying and synthesizing pattern information from multiple regions. This reference copy serves as a standardized template that eliminates the need for repeated precise measurements, enabling fast inspection while maintaining accuracy through comparison against the pre-established reference
Data Source
AI summary
An image reading unit reads image data obtained by imaging a sample in which a plurality of regions is disposed including a pattern formed based on identical design information. An evaluation value acquisition unit acquires, from among sampling images at a plurality of sampling points set for each of the plurality of regions, an evaluation value based on luminance of pixels for a plurality of sampling images at the same sampling point of the plurality of regions. A reference evaluation value acquisition unit acquires a reference evaluation value relative to the evaluation value for a plurality of sampling images at the same sampling point in the plurality of regions. An equalized evaluation value acquisition unit acquires an equalized evaluation value indicating a degree of deviation of the evaluation value from the reference evaluation value, for each of the sampling images of the plurality of regions.