EUV Mirror Substrate Microstructuring and Polishing
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Solution Overview
Problem
Existing reflective optical components for EUV projection exposure apparatuses face challenges in meeting stringent requirements for figure accuracy and roughness while being cost-effective, and they are inadequate under high thermal loads due to the limitations of substrate materials like glass and ceramics.
Innovation Solution
The method involves working optically operative microstructuring into the substrate, followed by polishing and applying a reflective layer, allowing the microstructuring to meet roughness requirements without initial precision, and using materials like metals or polymeric materials for cost-effectiveness and thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If glass or glass ceramic substrates are used for EUV mirrors, then figure accuracy and surface roughness can be achieved through superpolishing, but the cost of materials and processing becomes extremely high
Solution Approach 1:
The patent replaces expensive glass and glass ceramic substrates with cheaper alternative materials such as metals, metal alloys, semiconductors, or polymeric materials. These materials can be processed using conventional and low-priced machining methods like milling, turning, or eroding, thereby significantly reducing manufacturing costs while still achieving the required surface roughness through subsequent polishing steps
Solution Approach 2:
The patent changes the material parameters by selecting substrates with different physical and chemical properties that are more suitable for conventional processing. The key requirement is achieving a surface roughness of less than 0.2 nm rms, which can be accomplished through polishing regardless of the base material, thus decoupling the cost of raw materials from the final surface quality
2Manufacturing precision
If glass or glass ceramic substrates are used, then initial surface quality can be achieved, but thermal conductivity is insufficient under high radiation power
Solution Approach 1:
The patent employs composite material structures where a substrate with high thermal conductivity (such as metals or semiconductors) is combined with a thin cover layer that provides the necessary optical properties. This composite approach allows the bulk material to efficiently conduct heat away from the mirror surface while the thin surface layer maintains the required optical precision
Solution Approach 2:
The patent applies different material properties to different parts of the mirror structure. The bulk substrate material is selected for high thermal conductivity to handle heat dissipation, while only a thin surface layer (cover layer) is required to provide the precise optical surface. This local differentiation of material properties optimizes both thermal management and optical performance
3Adaptability or versatility
If microstructuring is applied to EUV mirrors using conventional methods, then optical functionality is achieved, but surface roughness requirements are no longer met
Solution Approach 1:
The patent performs microstructuring of the substrate before applying the final polishing step. By pre-structuring the substrate and then polishing the entire surface, the method achieves both the desired optical functionality from the microstructure and the required surface roughness precision, eliminating the need to choose between the two competing requirements
Data Source
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AI summary
A method for producing a reflective optical component (10) for an EUV projection exposure apparatus, said component having a substrate (12) having a base body (14), and a reflective layer (20) arranged on the substrate (12), wherein the substrate (12) has an optically operative microstructuring (16), comprises the following steps: working the microstructuring (16) into the substrate (12), polishing the substrate (12) after the micro-structuring (16) has been worked into the substrate (12), applying the reflective layer (20) to the substrate (12). A reflective optical component for an EUV projection exposure apparatus correspondingly has a polished surface between the microstructuring and the reflective layer.