Rectangular TDI Photodetector Pixels for Anamorphic Mask Inspection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In semiconductor inspection using Time Delay Integration (TDI) cameras, reducing pixel size to enhance resolution leads to a decrease in light reception area per pixel, resulting in a deteriorated signal-to-noise ratio and difficulty in maintaining contrast, especially when dealing with anamorphic masks with different reduction rates in the longitudinal and lateral directions.
Innovation Solution
A photodetector with rectangular pixels, where the ratio of dimensions in the longitudinal direction to the lateral direction matches the inverse ratio of the reduction rates in these directions, allowing for improved resolution in the required direction while maintaining contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size of the TDI sensor is reduced to increase resolution, then the resolution is improved, but the light receiving area per pixel is reduced and the signal-to-noise ratio deteriorates
Solution Approach 1:
The patent applies asymmetry by using rectangular pixels with different dimensions in the longitudinal and lateral directions. The pixel shape is specifically designed to match the anamorphic reduction rates, with the ratio of the dimension in the longitudinal direction to the dimension in the lateral direction being equal to the inverse ratio of the reduction rates. This asymmetric pixel geometry allows the sensor to maintain appropriate light reception area while achieving required resolution in the direction of highest demand.
Solution Approach 2:
The patent applies local quality by optimizing pixel dimensions specifically for the longitudinal direction where highest resolution is needed for mask inspection. The rectangular pixel configuration provides different dimensional characteristics in different directions, with the pixel being longer in the longitudinal direction to maintain light reception area while providing finer sampling in the lateral direction where resolution is most critical for defect detection.
2Measurement precision
If the pixel size is reduced to detect smaller defects, then the measurement precision is improved, but the contrast maintenance becomes difficult due to reduced light reception area
Solution Approach 1:
The asymmetric rectangular pixel configuration allows the sensor to maintain sufficient light reception area in the longitudinal direction while providing enhanced sampling density in the lateral direction. This asymmetry enables the system to detect smaller defects with high contrast by concentrating resolution improvements in the direction most critical for defect visibility, rather than uniformly reducing pixel size in all directions.
3Device complexity
If a conventional square pixel is used in an anamorphic optical system, then the device complexity is low, but the inspection quality deteriorates due to mismatch with different reduction rates
Solution Approach 1:
The patent transitions from symmetric square pixels to asymmetric rectangular pixels, where the aspect ratio of the pixel matches the inverse ratio of the anamorphic reduction rates. This geometric adaptation allows the sensor to properly sample the anamorphically reduced image, ensuring that defects are detected with appropriate resolution and contrast in both longitudinal and lateral directions, thereby significantly improving inspection quality.
Solution Approach 2:
The patent applies parameter changes by modifying the pixel dimensional parameters to match the optical system characteristics. The specific parameter adjustment involves setting the ratio of the pixel dimension in the longitudinal direction to the pixel dimension in the lateral direction equal to the inverse ratio of the reduction rates, thereby optimizing the sensor geometry for the specific anamorphic optical configuration.
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
Enables high-resolution inspection in the direction requiring it while preventing a decrease in contrast and inspection time due to reduced light reception area, effectively addressing the challenge of anamorphic masks with differing reduction rates.
Implementation Method 1
a photodetector for detecting light from a mask
Data Source
AI summary
Resolution is improved in a required direction while maintaining contrast in inspection of an anamorphic mask. A photodetector detects light from a mask with a reduction rate at the time of exposure in a longitudinal direction different from a reduction rate at the time of exposure in a lateral direction. The photodetector includes a rectangular pixel, a ratio of a dimension of the rectangular pixel in the longitudinal direction to a dimension of the rectangular pixel in the lateral direction being equal to an inverse ratio of the reduction rate in the longitudinal direction to the reduction rate in the lateral direction.