Lithography Mask Inspection System Edge Detection
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Solution Overview
Problem
Conventional mask inspection systems face challenges in accurately detecting the edges of lithography masks with chamfers, as the edges lie outside the depth of field of optical units, leading to unsharpness and requiring laborious adaptations for different mask sizes.
Innovation Solution
A mask inspection system with a dual optical unit configuration, where one unit examines structures and the other detects edges, using different wavelengths and optical elements to achieve high accuracy and adaptability without extensive reconstruction, allowing edge detection through the placement table without reflecting radiation, thus simplifying the setup and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional imaging optical unit is used to examine mask structures, then high measurement accuracy in the nanometer range is achieved, but the edges cannot be measured directly because they lie outside the depth of field, resulting in edge unsharpness of several hundred μm
Solution Approach 1:
The inspection system is divided into two separate optical units: a first optical unit for examining mask structures with high resolution, and a second optical unit specifically for detecting mask edges. This segmentation allows each unit to be optimized for its specific function, with the second unit using a small aperture to achieve sufficient depth of field for edge detection while the first unit maintains nanometer-range precision for structure examination.
2Difficulty of detecting and measuring
If the measuring table surface is made reflective to illuminate edges in reflected light, then edge detection becomes possible, but the surface must be individually processed and adapted for each mask size, which is laborious and time-consuming
Solution Approach 1:
The invention extracts the edge detection function from the structure examination function by using a separate second optical unit. This unit employs a small aperture to create sufficient depth of field, allowing edge detection without requiring the measuring table to be made reflective. The beam path can be configured to pass through or alongside the mask, eliminating the need for table surface processing and enabling quick adaptation to different mask sizes.
3Difficulty of detecting and measuring
If refocusing is performed to accommodate edges at different depths, then edge detection accuracy improves, but installation space requirements increase due to the need for additional optical adjustment mechanisms
Solution Approach 1:
The second optical unit is designed with a small aperture that provides sufficient depth of field locally for edge detection without requiring extensive refocusing capability. This localized optical design allows the system to maintain compact dimensions while achieving the necessary edge detection accuracy, as the small aperture inherently provides the depth of field needed for edges at chamfer depths without requiring large adjustment mechanisms.
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 accurate edge detection with sub-micron precision, reducing labor and time required for system adaptation, and minimizing installation space and optical components, while maintaining high resolution for structure examination.
Implementation Method 1
the second beam path of the second optical unit passes at least once through a plane defined by the placement table
Data Source
AI summary
One aspect of the present invention relates to a mask inspection system for inspecting lithography masks, including a placement table for placing a lithography mask to be inspected, a first optical unit with a first beam path for examining structures of the lithography mask, and a second optical unit with a second beam path for establishing a position of at least one edge of the lithography mask. Here, the second beam path of the second optical unit passes at least once through a plane defined by the placement table.