Phase Contrast Optical Method for EUV Mask Defect Localization
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Solution Overview
Problem
Existing methods for localizing defects on substrates for microlithographic projection exposure apparatuses and EUV lithography masks are inadequate, particularly at the boundary layer between the base substrate and the multilayer, leading to potential mask failure and inefficiencies in defect detection.
Innovation Solution
A phase contrast optical method using a phase mask and sensor device to detect phase shifts in illumination radiation, allowing for precise localization of buried defects between the base substrate and multilayer, with an annular phase mask and stop design for optimal imaging and a CCD camera for image analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inspection methods are used, then general defect detection is possible, but buried defects at the boundary layer between base substrate and multilayer cannot be detected with sufficient precision
Solution Approach 1:
The patent applies parameter changes by utilizing phase contrast microscopy to detect phase shifts in illumination radiation caused by buried defects. This optical parameter change enables visualization of defects at the boundary layer between base substrate and multilayer that are invisible to conventional inspection methods, achieving precise localization with accuracy better than 10 nm.
2Reliability
If multiple images are captured for defect analysis, then comprehensive defect information is obtained, but inspection time and processing complexity increase
Solution Approach 1:
The patent extracts the essential defect information by capturing a single phase contrast image that directly reveals buried defects through phase shift detection. This eliminates the need for multiple images and complex image processing, reducing inspection time while maintaining high reliability in defect detection and localization.
3Productivity
If substrates with defects are used for mask production, then productivity is maintained, but mask quality and reliability deteriorate
Solution Approach 1:
The patent performs preliminary inspection using phase contrast microscopy to detect and localize buried defects on substrates before mask production. This enables selective use of substrates - those with acceptable defect patterns can be used to maintain productivity, while defective substrates are identified and excluded, ensuring mask reliability without compromising production efficiency.
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 detection and localization of defects with high precision, reducing the need for multiple images and improving defect localization accuracy to less than 10 nm, while also allowing for the use of substrates with defects hidden under absorber layers, thus enhancing the efficiency of EUV mask production.
Implementation Method 1
detecting a phase shift brought about by the substrate of the illumination radiation by use of a sensor device arranged in the beam path downstream of the phase mask
Data Source
AI summary
In a method for localizing defects on a substrate for EUV masks, a phase contrast optical unit having a phase mask is used for examining the substrate.