EUV Mask Blank Glass Substrate with Precision-Polished Underlayer
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Solution Overview
Problem
Conventional methods for defect inspection in mask blanks for EUV lithography suffer from low position accuracy and difficulty in reusing or recycling substrates due to surface roughness issues, leading to false defect detection and increased manufacturing costs.
Innovation Solution
A mask blank glass substrate with a precision-polished underlayer on which a fiducial mark is formed to reduce surface roughness and enhance defect inspection accuracy, allowing for the recycling of the glass substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fiducial mark is formed directly on the glass substrate surface, then defect position can be specified, but surface roughness causes false defect detection and low inspection accuracy
Solution Approach 1:
An underlayer is introduced as an intermediary between the glass substrate and the fiducial mark. This underlayer serves as a mediator that provides a smooth surface for fiducial mark formation while being removable later, allowing the glass substrate to be reused without the permanent damage of direct surface etching. The underlayer absorbs the surface roughness issue while enabling accurate fiducial mark positioning.
Solution Approach 2:
The solution segments the functional requirements into separate layers: the glass substrate provides structural support and can be reused, the underlayer provides a smooth surface for fiducial mark formation and can be removed for recycling, and the fiducial mark provides positioning reference. This segmentation allows each layer to fulfill its specific function without compromising the others.
2Measurement precision
If the glass substrate surface is etched to form a fiducial mark, then defect position can be referenced, but the substrate cannot be reused or recycled
Solution Approach 1:
The underlayer acts as a sacrificial intermediary that can be removed after serving its purpose of providing a smooth surface for fiducial mark formation. This allows the glass substrate to be recovered and reused without permanent modification, solving the contradiction between creating an accurate reference mark and maintaining substrate recyclability.
Solution Approach 2:
The underlayer is designed to be discarded after use, while the glass substrate is recovered for reuse. This selective discarding and recovering approach allows the fiducial mark system to function accurately while preserving the valuable glass substrate for future use, thereby solving the reusability problem.
3Productivity
If conventional defect inspection methods are used, then inspection can be performed, but position accuracy is low and defects cannot be avoided with sufficient precision
Solution Approach 1:
The underlayer provides a distinct optical contrast against the glass substrate, creating a visible reference system that improves the detectability and positioning accuracy of defects during inspection. The fiducial marks on the underlayer create reference points that enhance measurement precision without requiring complex inspection equipment.
Data Source
AI summary
Provided is a mask blank glass substrate that has high surface smoothness, that is formed with a fiducial mark capable of improving the detection accuracy of a defect position or the like, and that enables reuse or recycling of a glass substrate included therein. An underlayer is formed on a main surface, on the side where a transfer pattern is to be formed, of a glass substrate for a mask blank. The underlayer serves to reduce surface roughness of the main surface of the glass substrate or to reduce defects of the main surface of the glass substrate. A surface of the underlayer is a precision-polished surface. A fiducial mark which provides a reference for a defect position in defect information is formed on the underlayer.