Inspection Apparatus Illumination Segmentation for Photomask Thickness Variations
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Solution Overview
Problem
Conventional inspection apparatuses face challenges in performing accurate inspections in a short time due to variations in photomask thickness, which affect the focal point and lead to aberrations, resulting in non-uniform illumination and blurred images, especially when trying to enlarge the transmission and reflection image picking-up areas to shorten inspection time.
Innovation Solution
The apparatus employs an objective lens with a reflected illumination optical system illuminating a first area and a transmitted illumination optical system illuminating both areas, with an adjusting unit to optimize the positions of the illumination light, allowing for detection of transmitted and reflected light by separate detectors to form combined and transmission images, and subtracting the transmission image from the combined image to obtain the reflection image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transmission image picking-up area and reflection image picking-up area are enlarged to shorten inspection time, then inspection speed is improved, but the illumination becomes non-uniform and images become blurred due to focal point deviation caused by photomask thickness variations
Solution Approach 1:
The patent divides the illumination field into two separate areas: a transmission image picking-up area and a reflection image picking-up area. By segmenting the illumination regions, the system can optimize illumination conditions for each area independently, ensuring uniform illumination and clear images while maintaining enlarged picking-up areas for fast inspection.
Solution Approach 2:
The patent applies different illumination qualities to different regions by providing dedicated transmitted illumination and reflected illumination optical systems for respective areas. This local optimization ensures that each picking-up area receives appropriate illumination conditions despite photomask thickness variations, maintaining image quality while enabling rapid inspection.
2Measurement precision
If separate sensors are used to detect transmission image and reflection image, then inspection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent combines the transmission image picking-up area and reflection image picking-up area within a single detection system framework. By integrating both illumination paths and detection paths into one unified system with coordinated optical elements, the patent achieves accurate simultaneous detection of transmission and reflection images while avoiding the complexity of completely separate sensor systems.
Solution Approach 2:
The patent designs the detection system to serve multiple functions: the same detection apparatus processes both transmission images and reflection images from different picking-up areas. This multi-functional approach maintains inspection accuracy for both image types while reducing overall device complexity through shared optical components and processing pathways.
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 accurate and efficient inspection by ensuring uniform illumination and clear images, even with varying photomask thickness, allowing for simultaneous detection of both transmission and reflection images, thus improving inspection speed and accuracy.
Implementation Method 1
a reflected illumination optical system that illuminates a first area which is part of a field of view of the objective lens from the objective lens side of the sample
Implementation Method 2
a transmitted illumination optical system that illuminates the first area and a second area which is the other part of the field of view of the objective lens than the first area from the opposite side of the sample from the objective lens
Data Source
AI summary
According to a first aspect of the present invention, there is provided an inspection apparatus including an objective lens, a reflected illumination optical system that illuminates a first area which is part of a field of view of the objective lens, a transmitted illumination optical system that illuminates the first area and a second area; an adjusting unit that adjusts positions on the sample of transmitted illumination light from the transmitted illumination optical system and reflected illumination light from the reflected illumination optical system; a first detector that detects a transmitted light transmitted by the sample and a reflected light reflected by the sample in the first area; and a second detector that detects through the objective lens a transmitted light transmitted by the sample in the second area.