EUV Mirror Substrate Compaction via Segmented Material Selection
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Solution Overview
Problem
Microlithographic EUV projection exposure apparatus face challenges with low mirror reflectivity and thermal issues due to the absorption of EUV light, leading to potential compaction of glass-based mirror substrates with low thermal expansion coefficients, which can degrade imaging quality over time.
Innovation Solution
The solution involves dividing the mirrors into first and second types based on their susceptibility to EUV light intensity, using materials like silicon or metal alloys for high-intensity mirrors and glass-based substrates for lower-intensity mirrors, and applying protective layers to prevent EUV light penetration, ensuring long-term stability and minimizing compaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If glass-based mirror substrates with low thermal expansion coefficients are used to reduce thermal deformations, then thermal stability is improved, but compaction of the mirror substrate occurs under EUV light irradiation, degrading imaging quality over time
Solution Approach 1:
The patent segments the mirror system into two distinct groups: first mirrors made from materials resistant to compaction (silicon, metal alloys, or glass with compensating deformations) and second mirrors made from glass-based substrates with low thermal expansion coefficients. This segmentation allows each group to be optimized for its specific function, resolving the contradiction between thermal stability and compaction resistance
Solution Approach 2:
The patent applies local quality by assigning different material properties to different mirrors based on their position and function in the optical system. First mirrors (which receive higher EUV light intensity) use materials with compaction resistance, while second mirrors (which receive lower intensity) use glass-based substrates optimized for thermal stability. This localized optimization resolves the contradiction by matching material properties to specific operational conditions
2Productivity
If the number of mirrors is reduced to minimize light losses, then productivity is improved, but thermal problems increase since heat must be dissipated through the mirror substrate in vacuum conditions
Solution Approach 1:
The patent changes the material parameters of mirror substrates to simultaneously address both light throughput and heat dissipation. By selecting materials with appropriate thermal conductivity and heat capacity characteristics, the system maintains high light throughput while ensuring effective heat dissipation through the substrate in vacuum conditions
Data Source
AI summary
A projection objective for a microlithographic EUV projection exposure apparatus includes a first mirror and a second mirror. The first mirror includes a mirror substrate and a reflective coating carried by the mirror substrate. The second mirror includes a mirror substrate and a reflective coating carried by the mirror substrate. The first and second mirrors are configured so that, with otherwise equal irradiation by EUV light, the mirror substrate of the first mirror compacts less than the mirror substrate of the second mirror under the effect of the EUV light.