Monolithic Decoupling Elements for EUV Mirror Support
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Solution Overview
Problem
In microlithographic projection exposure apparatuses, high numerical apertures lead to parasitic forces and moments that cause unwanted surface deformation in optical elements like mirrors, limiting natural frequencies and affecting imaging quality, especially in EUV lithography where thin mirrors are used.
Innovation Solution
The optical arrangement incorporates monolithic decoupling elements formed with the optical and support elements, eliminating the need for separate joining technologies and reducing parasitic forces by using a three-point decoupling effect, which provides sufficient stiffness and minimizes deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high numerical aperture is used in EUV projection objectives, then imaging resolution is improved, but parasitic forces and moments cause unwanted surface deformation in mirrors
Solution Approach 1:
The mirror support structure is segmented into multiple independent support points (at least three) that are spatially distributed. Each support point independently bears load, preventing the transmission of parasitic forces and moments across the entire mirror surface. This segmentation allows the mirror to maintain its intended shape while supporting high numerical aperture imaging requirements.
Solution Approach 2:
The support structure provides localized support at specific discrete points rather than continuous support across the mirror surface. Each support location is optimized to provide exactly the necessary support without over-constraint, allowing different regions of the mirror to have different support characteristics appropriate to their local stress requirements.
2Length of stationary object
If mirror thickness is reduced to achieve smaller spacing in high-aperture objectives, then device compactness is improved, but natural frequencies decrease and stiffness is reduced
Solution Approach 1:
The support system is divided into multiple discrete support points rather than a single continuous support. This segmentation allows each support point to be optimized for local load bearing while the overall distributed support system maintains the mirror's global stiffness and natural frequencies even with reduced mirror thickness.
Solution Approach 2:
The support structure combines the mirror substrate with a separately designed support element structure. The mirror can be made thin for compactness while the support elements provide the necessary mechanical strength and stiffness through their own structural design, creating a composite system that achieves both compactness and structural integrity.
3Ease of manufacture
If traditional joining technologies are used to attach mirrors to holders, then ease of assembly is improved, but parasitic forces and moments are introduced causing deformation
Solution Approach 1:
The mirror and support element are merged into a single monolithic component formed from one piece of material. This eliminates the need for separate joining technologies (adhesives, mechanical fasteners, etc.) that would introduce parasitic forces and moments. The integrated structure ensures that support forces are distributed evenly without the deformation-causing effects of traditional joining methods.
Solution Approach 2:
The invention converts the potential harm of rigid connections (which transmit parasitic forces) into a benefit by using a monolithic structure that inherently distributes forces evenly. The integrated design transforms what would be a source of deformation (connection points) into a source of uniform support, eliminating the need for separate joining processes.
Data Source
AI summary
An optical arrangement includes at least one optical element and a support element for the optical element. The optical element and the support element are connected together by way of at least three decoupling elements. The decoupling elements are formed monolithically with the optical element and with the support element.