Segmented EUV Membrane Assembly for Optical Protection
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Solution Overview
Problem
EUV lithography systems face challenges in protecting large optical elements from contaminating substances like tin particles, which can lead to surface contamination, blistering, and impairment of mechanical components due to the limitations of single-piece membranes, including bending issues and shading by non-transparent frames.
Innovation Solution
A multi-part membrane assembly with segmented membrane segments mounted on a self-supporting frame, optimized for EUV radiation transparency and stability, along with a coating to reduce contamination and a purge system to maintain a clean environment, effectively covers large optical surfaces while minimizing shading and mechanical interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a single-piece membrane is used to protect the optical element surface, then the membrane provides continuous coverage, but the membrane bends due to lack of self-supporting capability
Solution Approach 1:
The membrane is divided into multiple membrane segments (first, second, third, and fourth membrane segments) that are arranged in a grid pattern. Each segment is supported by the frame structure, providing self-supporting capability and preventing bending while maintaining continuous coverage of the optical element surface.
Solution Approach 2:
The protective structure combines multiple membrane segments with a frame structure to create a composite system. The frame provides mechanical support while the membrane segments provide contamination protection, achieving both structural stability and protective function.
2Stability of the object's composition
If a frame structure is added to support the membrane, then the membrane gains self-supporting capability, but the frame causes shading of the optical element
Solution Approach 1:
The frame is segmented into multiple sections with webs positioned at specific locations. The membrane segments are arranged in a grid pattern corresponding to the frame segmentation, allowing the frame to provide support while minimizing the shaded area through strategic positioning of support elements.
Solution Approach 2:
The frame structure is designed with varying web thicknesses and positions tailored to specific regions. The web width and spacing are optimized locally to provide adequate membrane support while minimizing shading in critical optical paths. Different regions of the optical element receive differentiated support and shading protection.
3Stability of the object's composition
If the membrane thickness is increased to prevent bending, then the membrane gains structural stability, but the absorption of EUV radiation increases
Solution Approach 1:
Instead of increasing membrane thickness, the membrane is segmented into multiple thin sections supported by the frame. Each segment remains thin to minimize EUV absorption while the frame structure provides the necessary rigidity and support, distributing mechanical loads across multiple support points.
Solution Approach 2:
The patent employs thin membrane segments that are flexible yet effective for contamination protection. These thin films minimize EUV radiation absorption while the frame structure compensates for the reduced inherent rigidity, maintaining overall structural stability through external support.
4Strength
If the frame webs are made wider to better support the membrane segments, then the support capability increases, but the shading of the optical element increases
Solution Approach 1:
The web width and support capability are optimized locally for each region. Webs are positioned and sized according to the specific mechanical requirements of adjacent membrane segments and the optical constraints of the underlying optical element, achieving adequate support with minimal shading in each local region.
Solution Approach 2:
The frame provides support slightly beyond the minimum required, with membrane segments extending slightly beyond the web edges. This partial overlap ensures adequate support capability while keeping web widths minimal to reduce shading, balancing support strength with optical transmission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly increases the protected surface area, reduces contamination, and maintains optical element functionality by using a segmented membrane assembly with a frame that is transparent to EUV radiation, ensuring effective protection against tin particles and other contaminants in EUV lithography systems.
Implementation Method 1
a protective element for protecting a surface of the optical element from contaminating substances, the protective element comprising a membrane
Implementation Method 2
a frame on which the membrane is mounted
Implementation Method 3
optimized for EUV radiation transparency
Implementation Method 4
along with a coating to reduce contamination
Implementation Method 5
and a purge system to maintain a clean environment
Data Source
AI summary
An optical assembly includes an optical element (13), configured in particular for the reflection of EUV radiation (4), and a protective element (30) for protecting a surface (31) of the optical element (13, 14) from contaminating substances (P). The protective element (30) has a membrane (33a-c) and a frame (34) on which the membrane (33a-c) is mounted. The membrane is formed by a plurality of membrane segments (33a, 33b, 33c) which respectively protect a partial region (T) of the surface (31) of the optical element (13) from the contaminating substances (P). The optical assembly can form part of an overall optical arrangement, for example an EUV lithography system.