Mask Blank Substrate Flatness Control for High-NA EUV Exposure
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Solution Overview
Problem
Existing mask blank substrates for EUV lithography do not adequately address the issue of positional deviation (IPE) during exposure due to direction-dependent flatness, especially in high NA generation, and lack high productivity in achieving uniform flatness across wide exposure areas.
Innovation Solution
The mask blank substrate is separated into X and Y direction components, with differing flatness values, and produced using localized processing to achieve a PV ratio of ⅓ or less, ensuring high flatness and reduced IPE, particularly in high NA EUV exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If double-sided simultaneous polishing is used to produce glass substrate, then productivity is improved, but flatness is insufficient for EUV lithography
Solution Approach 1:
The polishing process is segmented into multiple stages: initial polishing to achieve basic flatness, followed by localized processing to correct specific surface irregularities, and final polishing to achieve the required high flatness. This segmentation allows each stage to optimize for its specific goal, maintaining productivity while improving precision.
Solution Approach 2:
Localized processing techniques are applied to specific regions of the substrate surface where convexities or irregularities are detected. Instead of treating the entire surface uniformly, the method applies polishing pressure and abrasives selectively to areas needing correction, achieving high flatness without requiring excessive overall processing time.
2Manufacturing precision
If conventional polishing techniques are advanced to improve flatness, then manufacturing precision is improved, but productivity decreases
Solution Approach 1:
Surface shape measurement and analysis are performed before the final polishing stage to identify and map convex regions in advance. This preliminary characterization allows the localized processing to be targeted more effectively, reducing the number of trial-and-error polishing cycles and achieving high flatness faster.
Solution Approach 2:
The surface shape is measured and evaluated at intermediate stages of the polishing process. Based on this feedback, the localized processing parameters (such as polishing pressure, abrasive concentration, and treatment duration) are adjusted to optimize flatness correction while minimizing additional processing time. This closed-loop control prevents over-processing and maintains high productivity.
3Manufacturing precision
If uniform flatness is achieved across the entire substrate, then manufacturing precision is improved, but the complexity of processing increases
Solution Approach 1:
The processing system is designed to apply different polishing intensities and parameters to different regions of the substrate based on their specific surface characteristics. The localized processing apparatus can selectively treat convex regions with higher polishing pressure while leaving concave regions unchanged, achieving uniform overall flatness through differentiated local treatment rather than uniform processing.
Data Source
AI summary
A mask blank substrate in which when a rectangular region which is surrounded by four sides that are located at 5 mm from four sides of a rectangular main surface of 152 mm or more×152 mm or more in an inward direction and are parallel to the four sides of the main surface and in which an intersection of diagonal lines of the main surface forms a center is defined, the flatness of the rectangular region is 100 nm or less, and when the surface shape of the rectangular region is separated into an X direction component (Sx) and a Y direction component (Sy), and of a difference PVx between the maximum height and the minimum height of Sx and a difference between the maximum height and the minimum height of Sy, the smaller is PVmin and the larger is PVmax, PVmin/PVmax is ⅓ or less.