Photomask Blank Substrate Polishing for Vacuum Chuck Warping
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Solution Overview
Problem
The challenge in photolithography for semiconductor manufacturing is achieving high accuracy in pattern formation due to the deformation of photomasks caused by vacuum chucks, which leads to focal shift and warping of substrates, especially as feature sizes decrease, and there is a lack of methods to produce substrates with specific surface shapes to mitigate these issues.
Innovation Solution
A method for producing quadrangular photomask blank substrates with specific strip-like or ring-shaped regions on the top surface, polished to precise height differences, which minimizes warping when held by a vacuum chuck, allowing for accurate alignment and exposure pattern precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a photomask is held on a mask stage with a vacuum chuck, then the photomask can be secured for exposure, but the overall surface shape of the photomask is greatly deformed causing focal shift
Solution Approach 1:
The substrate surface is pre-formed with a specific shape (convex center, concave periphery) before photomask fabrication. This preliminary shaping compensates for the vacuum chuck deformation that will occur during exposure, ensuring the photomask maintains proper flatness when held.
Solution Approach 2:
The substrate surface is pre-formed with a specific shape (convex center, concave periphery) before photomask fabrication. This preliminary shaping compensates for the vacuum chuck deformation that will occur during exposure, ensuring the photomask maintains proper flatness when held.
2Adaptability or versatility
If the minimum feature size is reduced for higher integration, then device capability is improved, but the focal depth allowed by resist becomes smaller making substrate flatness critical
Solution Approach 1:
The substrate surface is pre-formed with a specific shape (convex center, concave periphery) before photomask fabrication. This preliminary shaping compensates for the vacuum chuck deformation that will occur during exposure, ensuring the photomask maintains proper flatness when held.
Solution Approach 2:
The substrate surface geometry is changed from a conventional flat or uniformly polished shape to a specific three-dimensional profile with convex center and concave periphery. This parameter change in surface shape allows compensation for vacuum chuck effects and maintains adequate focal depth even when minimum feature sizes are reduced.
3Manufacturing precision
If the substrate surface is polished to reduce defects and minimize warpage, then surface quality is improved, but the specific shape needed for vacuum chuck compensation is not achieved
Solution Approach 1:
Different regions of the substrate surface are given different shapes: the center region is formed convex while the periphery is formed concave. This local differentiation of surface geometry allows the substrate to compensate for vacuum chuck deformation while maintaining high overall surface quality.
Solution Approach 2:
The substrate surface is pre-formed with a specific shape (convex center, concave periphery) before photomask fabrication. This preliminary shaping compensates for the vacuum chuck deformation that will occur during exposure, ensuring the photomask maintains proper flatness when held.
Data Source
AI summary
A photomask blank substrate is made by polishing a starting substrate to a specific flatness in a principal surface region on a top surface of the substrate so as to form a polished intermediate product, then additionally polishing the intermediate product. Substrates made in this way exhibit a good surface flatness at the time of wafer exposure. When a photomask fabricated from a blank obtained from such a substrate is held on the mask stage of a wafer exposure system with a vacuum chuck, the substrate surface undergoes minimal warping, enabling exposure patterns of small geometry to be written onto wafers to good position and linewidth accuracies.