EUV Mask Blank Substrate Composition for Yield and Thermal Stability
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Solution Overview
Problem
Manufacturing low thermal expansion glass substrates for EUV lithography masks is challenging due to local compositional non-uniformities, leading to low production yield and difficulty in achieving desired thermal expansion properties.
Innovation Solution
A mask blank substrate design with specific regions allowing for locally non-uniform TiO2/SiO2 content variations, particularly within 500 μm depth from the surface, ensuring a Ti/Si ratio difference of 0.25% or more and a variation of 0.06 mass% or less, while maintaining overall thermal expansion compatibility and polishing integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If visual inspection is performed to remove substrates with locally non-uniform composition, then substrate quality is improved, but production yield deteriorates
Solution Approach 1:
The patent applies local quality by permitting locally non-uniform portions in specific regions (second and third regions) of the substrate while maintaining strict uniformity in the first region where the reflective film is formed. This allows substrates with localized compositional variations to be accepted if they meet the uniformity requirement in the critical first region, thereby reducing rejection rates and improving production yield without compromising mask performance
2Stability of the object's composition
If low thermal expansion glass is used to avoid distortion under EUV light irradiation, then thermal stability is improved, but manufacturing difficulty increases due to compositional non-uniformity
Solution Approach 1:
The patent segments the substrate into three distinct regions with different compositional requirements: the first region (where the reflective film is formed) requires strict compositional uniformity, while the second and third regions permit locally non-uniform portions. This segmentation allows the substrate to achieve thermal stability in the critical area while accommodating manufacturing variations in non-critical areas, thereby improving ease of manufacture without sacrificing thermal stability
Solution Approach 2:
The patent applies local quality by specifying different compositional uniformity standards for different regions of the substrate. The first region maintains strict uniformity to ensure thermal stability under EUV irradiation, while the second and third regions allow for locally non-uniform portions, making the material easier to manufacture while preserving the required thermal performance
Data Source
AI summary
A mask blank substrate includes two opposing main surfaces, has a glass material containing SiO2 and TiO2, and has a first region in one main surface side. The first region is a region within a square including a center portion in the one main surface and which is a region extending from the one main surface toward the other main surface up to a position in depth. An inner region of the substrate excluding the first region has a locally non-uniform portion, a ratio of Ti content rate to Si content rate (Ti/Si) of the non-uniform portion differs from Ti/Si of the inner region excluding the non-uniform portion by 0.25% or more, and the variation of Ti content rate in the inner region of the substrate excluding the first region and the non-uniform portion is 0.06 mass % or less.