Photolithography Mask Inspection Using Transmitted and Reflected Light
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Solution Overview
Problem
Current pattern inspection methods for photolithography masks struggle to achieve high accuracy in position and line width dimensional control, especially as pattern sizes on semiconductor wafers continue to miniaturize, leading to difficulties in defect detection and correction.
Innovation Solution
An inspection apparatus and method that irradiates a sample with lighting light to obtain optical images, compares these images with reference images, creates defect maps, and determines the necessity and appropriateness of defect corrections using a combination of transmitted and reflected light images, along with defect correction method information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single optical image (transmitted or reflected light) is used for inspection, then the inspection process is simple, but the measurement precision and manufacturing precision are insufficient for miniaturized patterns
Solution Approach 1:
The patent combines transmitted light images and reflected light images into a single integrated inspection system. The image acquisition unit captures both types of optical images simultaneously or sequentially, and the image processing unit fuses these images to create comprehensive defect maps, thereby improving measurement precision without requiring separate inspection systems
Solution Approach 2:
The patent transitions from single-dimensional (single optical image type) inspection to multi-dimensional inspection by incorporating both transmitted light and reflected light images. This adds an additional dimension of information about the mask pattern, enabling more accurate detection of position and line width variations in miniaturized patterns
2Measurement precision
If traditional single-image comparison methods are used, then the inspection method is simple, but the detection precision cannot meet the requirements for ultra fine pattern defects
Solution Approach 1:
The patent segments the inspection process into distinct functional units: an image acquisition unit that captures transmitted and reflected light images, an image processing unit that creates defect maps by comparing images with reference data, and a determination unit that identifies defects. This segmentation allows for sophisticated multi-image processing while maintaining system manageability
Solution Approach 2:
The patent introduces an intermediate defect map as a processed representation that bridges the gap between raw optical images and final defect determination. The defect map synthesizes information from multiple images and comparisons, making the complex processing results interpretable and actionable
3Productivity
If strict allowable values for pattern defects are set, then manufacturing precision can be maintained, but the productivity and yield are reduced due to excessive defect rejections
Solution Approach 1:
The patent implements a feedback mechanism where the defect determination unit provides information about detected defects back to the image processing unit. This allows for dynamic adjustment of inspection criteria and enables differentiation between critical defects that require rejection and minor variations that can be tolerated, thereby improving manufacturing yield while maintaining necessary precision
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 enables highly accurate inspection and correction of photolithography masks, improving position accuracy and line width dimensional accuracy, thereby enhancing manufacturing yield and reducing the risk of pattern defects.
Implementation Method 1
a first optical image formed by the lighting light transmitted through the sample to be inspected
Implementation Method 2
a second optical image formed by the lighting light reflected by the sample to be inspected
Data Source
AI summary
An inspection apparatus includes a lighting unit, an imaging unit, an optical image comparison unit, a map creation unit, a map storage unit, a first storage unit, a map comparison unit, and a first determination unit. The lighting unit irradiates a sample including a defect to be inspected with a lighting light. The imaging unit obtains either or both of a first optical image formed by the lighting light transmitted through the sample to be inspected and a second optical image formed by the lighting light reflected by the sample to be inspected and obtains either or both of a third optical image formed by the lighting light transmitted through the sample to be inspected and having a corrected defect and a fourth optical image formed by the lighting light reflected by the sample to be inspected and having a corrected defect. The optical image comparison unit performs either or both of a first comparison between a first reference image referenced from an optical image formed by the lighting light transmitted through the sample to be inspected and the first optical image and a second comparison between a second reference image referenced from an optical image formed by the lighting light reflected by the sample to be inspected and the second optical image and performs either or both of a third comparison between the first reference image and the third optical image and a fourth comparison between the second reference image and the fourth optical image. The map creation unit creates either or both of a first map of the sample to be inspected based on the first comparison and a second map of the sample to be inspected based on the second comparison and creates either or both of a third map of the sample to be inspected based on the third comparison and a fourth map of the sample to be inspected based on the fourth comparison. The map storage unit stores either or both of the first map and the second map. The first storage unit stores defect correction method information on the defect. The map comparison unit performs either or both of a fifth comparison between the first map and the third map based on the defect correction method information and a sixth comparison between the second map and the fourth map based on the defect correction method information. The first determination unit determines, based on the defect correction method information and either or both of the fifth comparison and the sixth comparison, whether the correction is appropriate.