Mask Blank Substrate Selection via Floating Distance for High-NA Exposure
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Solution Overview
Problem
High-NA exposure apparatuses face significant focus errors when using non-high-spec mask blank substrates for semiconductor device manufacturing, leading to reduced resolution and increased costs due to the need for high-spec substrates for fine patterns and low-spec substrates for sparse patterns, which are not effectively distinguished by conventional flatness criteria.
Innovation Solution
A method for manufacturing mask blank substrates involves setting specific points on the substrate, calculating a floating distance between these points and the imaginary plane, and selecting substrates with a floating distance of less than 0.2 μm to minimize focus errors, using a least square plane approximation and root mean square roughness of 0.25 nm or less to ensure substrate quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional flatness criteria are used to select mask blank substrates, then substrate selection is simplified, but focus errors occur during high-NA exposure transfer
Solution Approach 1:
The patent changes the selection parameter from conventional flatness (maximum-minimum height difference) to floating distance (distance from imaginary plane passing through four corner points). This parameter transformation enables more accurate prediction of focus behavior during high-NA exposure while maintaining a relatively simple measurement and calculation process.
2Reliability
If high-spec mask blank substrates are used for fine patterns, then focus accuracy is improved, but manufacturing costs increase
Solution Approach 1:
The patent applies local quality by evaluating substrate flatness specifically at the four corner regions (calculation region) rather than requiring uniform high flatness across the entire substrate. This allows use of substrates with lower overall specifications while maintaining adequate flatness where it matters most for exposure accuracy.
3Productivity
If non-high-spec substrates are used to reduce costs, then manufacturing efficiency improves, but focus errors increase leading to reduced resolution
Solution Approach 1:
The patent enables use of cheaper, lower-specification substrates by introducing a new selection criterion (floating distance) that identifies substrates suitable for high-NA exposure. This transforms previously rejected low-cost substrates into acceptable materials, improving manufacturing efficiency without sacrificing pattern resolution.
4Reliability
If strict flatness requirements are imposed on all substrates, then focus errors are reduced, but substrate availability and manufacturing flexibility decrease
Solution Approach 1:
The patent transforms the selection parameter from strict uniform flatness requirements to floating distance measurement, which specifically evaluates the tilt condition of the substrate surface. This parameter change provides better correlation with focus behavior and allows greater flexibility in substrate selection while maintaining focus stability.
Data Source
AI summary
A mask blank substrate and a method for selecting a mask blank substrate wherein a square calculation region is set on the main surface of the substrate. Specific points are set at the corner portions of the calculation region. The heights of the specific points from a reference plane are acquired, an imaginary plane passing through three of the specific points is set, an intersection between the imaginary plane and a perpendicular line that passes through the remaining of the specific points and that is perpendicular to the reference plane is set, and the distance between the remaining of the specific points and the intersection is calculated. A substrate in which the distance satisfies a predetermined reference value is selected as a mask blank substrate.