Gray Level Ratio Inspection Dark Level Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Gray level ratio calculations in GLR inspection are prone to significant errors due to changes in the reference dark level, which can be influenced by factors such as illumination and photomultiplier voltage supply variations, necessitating an accurate compensation method.
Innovation Solution
A system and method for GLR inspection with dark level compensation, where a reference dark level value is calculated and subtracted from gray level values of structural elements within a region of interest and a reference region, allowing for accurate gray level ratio calculations by using a raster scan pattern and electron images to determine defect presence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference dark level is calculated periodically (one per several months), then device operation is simple, but measurement precision deteriorates due to dark level changes from illumination and collection variations
Solution Approach 1:
The patent applies preliminary action by calculating and storing reference dark level values at multiple predetermined voltage supply levels before actual inspection. These pre-calculated reference values are then used to compensate for dark level changes during inspection, eliminating the need for frequent recalibration while maintaining measurement accuracy.
Solution Approach 2:
The patent changes the parameter of reference dark level from a single fixed value to multiple values corresponding to different voltage supply levels. By selecting the reference dark level that matches the actual voltage supply condition, the system compensates for dark level variations without adding complex real-time adjustment mechanisms.
2Measurement precision
If reference dark level is updated frequently, then measurement precision improves, but loss of time increases due to repeated recalibration
Solution Approach 1:
The patent performs the time-consuming dark level calibration process in advance at multiple voltage levels and stores the results. During actual inspection, the pre-calibrated reference values are simply retrieved and applied, eliminating repeated recalibration time while maintaining accuracy across voltage variations.
Solution Approach 2:
The patent creates copies of reference dark level values for different voltage supply conditions. Instead of performing full recalibration each time voltage changes, the system copies and applies the appropriate pre-measured reference value, dramatically reducing time loss while maintaining measurement precision.
3Measurement precision
If dark level compensation is implemented, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent manages device complexity by organizing reference dark level data as a simple lookup table indexed by voltage supply level. The compensation mechanism only requires selecting the appropriate reference value based on current voltage conditions and applying it to the gray level calculation, avoiding complex real-time compensation algorithms.
Solution Approach 2:
The patent introduces a simple intermediary reference dark level value that mediates between the raw pixel values and the final gray level ratio calculation. This intermediary step corrects for dark level offsets without requiring complex processing, maintaining measurement precision while adding minimal system complexity.
Data Source
AI summary
A method for gray level ratio inspection comprising: obtaining an electron image that comprises region of interest (ROI) pixels of a ROI of the sample and reference pixels of a reference region of the sample, where the ROI pixels are obtained by illuminating the ROI with the electron beam and the reference pixels are obtained without illuminating the reference region with an electron beam; calculating a reference dark level value based on values of at least some of the reference pixels; calculating, responsive to the reference dark level value, a gray level ratio between a first gray level value related to a first sub-set of the ROI pixels and a second gray level value related to a second sub-set of the ROI pixels; determining whether the gray level ratio is indicative of a defect; and generating defect information following a determination that the gray level ratio is indicative of the defect.