Mask Blank Substrate Set with Convex Center Flatness
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Solution Overview
Problem
In photolithography processes for semiconductor manufacturing, the miniaturization of devices requires higher overlay accuracy of photomasks, which is compromised by differences in substrate flatness and deformation when vacuum-chucked in exposure apparatuses, leading to position offsets and reduced focus latitude.
Innovation Solution
A mask blank substrate set with substrates having a convex shape at the center and low at the periphery, with a flatness of 0.3 μm or less in a 142 mm square area, and a difference of 40 nm or less when fitted to a reference substrate, ensuring consistent deformation and high overlay accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If substrates with different main surface shapes are used in a photomask set, then each substrate can be optimized for its individual photomask, but the overlay accuracy between layers is degraded due to different deformation tendencies when vacuum-chucked
Solution Approach 1:
The patent applies homogeneity by requiring all substrates in the photomask set to have substantially the same main surface shape parameters (convex shape with center height 2-10 μm, flatness 0.3 μm or less, and specific curvature radius 10,000-50,000 mm). This ensures uniform deformation behavior across all substrates when vacuum-chucked, thereby maintaining high overlay accuracy between layers while allowing each substrate to be optimized for its specific photomask requirements.
2Reliability
If the flatness of substrate main surfaces is improved to enhance focus latitude, then position offset of transfer patterns is reduced, but the complexity of substrate manufacturing and selection increases
Solution Approach 1:
The patent applies parameter changes by specifying precise quantitative parameters for substrate main surface shape: convex shape with center height of 2-10 μm, flatness of 0.3 μm or less in a 142 mm square area, and curvature radius of 10,000-50,000 mm. These standardized parameter ranges achieve high focus latitude and reduced position offset while providing clear manufacturing criteria that reduce selection complexity.
3Manufacturing precision
If substrates with higher flatness are selected to reduce position offset, then overlay accuracy improves, but the availability and productivity of substrate selection is reduced due to stricter requirements
Solution Approach 1:
The patent applies preliminary action by pre-defining acceptable parameter ranges for substrate main surface shapes (convex shape, center height 2-10 μm, flatness 0.3 μm or less, curvature radius 10,000-50,000 mm) before the photomask set is assembled. This allows substrates to be pre-screened and categorized according to these criteria, enabling rapid selection of compatible substrates while ensuring high overlay accuracy, thus improving both precision and productivity.
Data Source
AI summary
A substrate set is a mask blank substrate set including a plurality of substrates each for use in a mask blank for producing a photomask to be chucked on a mask stage of an exposure apparatus. In each of the substrates in the mask blank substrate set, a main surface, on the side where a thin film for forming a transfer pattern is to be formed, has a convex shape being relatively high at its center and relatively low at its peripheral portion. In each substrate, the flatness in a 142 mm square area, including a central portion, of the main surface is 0.3 μm or less and the difference upon fitting to a reference main surface of a reference substrate is 40 nm or less.