Inspection Apparatus Drift Correction for Mask Defect Detection
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Solution Overview
Problem
Existing inspection apparatuses face challenges in accurately and efficiently matching optical images of ultrafine patterns on masks with reference images due to positional drift caused by temperature changes and air flow fluctuations, leading to increased calculation time and potential errors in defect detection.
Innovation Solution
The inspection apparatus virtually divides the sample into strip-shaped stripes and uses an offset value to adjust the acquisition position, determining a shift amount and evaluating its reliability to minimize the influence of drift, thereby enabling rapid and accurate matching of optical and reference images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mask is illuminated and optical images are acquired repeatedly for defect inspection, then defect detection capability is improved, but the inspection time increases due to the need to match positions of multiple images
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing drift correction values based on positional information from multiple optical images. Instead of performing time-consuming position matching during actual defect inspection, the system prepares correction data in advance, allowing rapid defect detection without repeated position alignment operations.
Solution Approach 2:
The patent creates a reference image from design data that serves as a template for comparison. By generating this reference copy in advance and using it for defect detection against acquired optical images, the system avoids the need to match positions between multiple acquired images, significantly reducing inspection time while maintaining defect detection accuracy.
2Measurement precision
If position matching is performed between acquired optical images and reference images, then measurement precision is improved, but calculation time increases due to drift correction requirements
Solution Approach 1:
The system performs preliminary drift correction by calculating correction values from positional information of patterns in multiple optical images before actual defect inspection. These pre-calculated correction values are stored and applied during inspection, eliminating the need for time-consuming real-time position matching while maintaining high measurement precision.
Solution Approach 2:
The patent replaces the mechanical position matching process with a computational approach using drift correction values. Instead of performing complex image alignment calculations during inspection, the system uses pre-computed correction data to adjust positions, substituting iterative mechanical matching with direct computational correction.
3Manufacturing precision
If the table and sample are moved precisely to determine optical image positions, then manufacturing precision is improved, but the system becomes sensitive to temperature changes and air flow fluctuations
Solution Approach 1:
The patent implements feedback by continuously monitoring the positions of patterns in multiple optical images and using this information to calculate drift correction values. This feedback mechanism compensates for temperature changes and air flow fluctuations by detecting actual positional shifts and correcting for them, maintaining manufacturing precision despite environmental variations.
Solution Approach 2:
The system changes the parameter being measured from absolute position (which is sensitive to environmental factors) to relative drift correction values derived from pattern positions in multiple images. By working with these corrected parameters, the system maintains precision while becoming insensitive to temperature and air flow changes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise and efficient matching of optical and reference images, reducing the impact of positional drift and improving the accuracy of defect detection in ultrafine patterns, particularly in miniaturized semiconductor and display device manufacturing.
Implementation Method 1
an optical image of the pattern is acquired from the light reflected from the mask or from the light transmitted through the mask
Data Source
AI summary
An inspection apparatus according to an embodiment includes: an optical image acquisition circuitry virtually dividing a sample into strip-shaped stripes, and acquiring an optical image; a reference image generation circuitry generating a reference image corresponding to the optical image; a comparison circuitry comparing the optical image and the reference image; a shift amount determination circuitry determining a shift amount between the optical image and the reference image, and generating an evaluation value; and an offset value calculation circuitry determining usage of the shift amount, and calculating an offset value for adjusting an acquisition position of the optical image. In a case where the offset value is calculated, the optical image acquisition circuitry acquires the optical image based on the offset value.