Variable-Stiffness Field Facets for EUV Pupil-Filling Focus
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Solution Overview
Problem
In EUV lithography apparatuses, the defocusing of images on pupil facets due to varying distances between field and pupil facets during switching positions limits the degree of pupil filling, which in turn affects the resolution and efficiency of the projection system.
Innovation Solution
A field facet system with an elastically deformable optical element that introduces a bending moment to adjust the curvature of the facet portion, allowing it to flex without torsion, and features variable stiffness along its longitudinal direction to maintain optimal imaging alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the field facet is switched between different pupil facets, then the illumination coverage is improved, but the distance variation causes image defocusing that limits pupil filling
Solution Approach 1:
The facet portion is designed to be elastically deformable with variable stiffness along its longitudinal direction, allowing it to dynamically change its curvature radius in response to switching positions. This dynamic adaptation enables the facet to maintain proper focus across different pupil facets while preserving illumination coverage
Solution Approach 2:
The curvature radius of the optically effective surface is changed by introducing a bending moment through actuating elements. By controlling the bending moment, the system adjusts the curvature parameter to compensate for distance variations during switching, thereby maintaining image focus precision across different pupil facets
2Manufacturing precision
If the curvature radius of the optically effective surface is changed to reduce defocusing, then the image focus is improved, but the structural complexity increases
Solution Approach 1:
The optical element is divided into a facet portion with different stiffness characteristics along its longitudinal direction. This segmentation allows different regions to have optimized mechanical properties, enabling curvature adjustment while maintaining overall structural simplicity and manufacturability
Solution Approach 2:
The facet portion is designed as an elastically deformable structure that can change its curvature radius when a bending moment is applied. This flexible design allows for simple structural implementation of curvature adjustment without requiring complex mechanical mechanisms
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 system enhances the degree of pupil filling and improves resolution by ensuring precise focusing across different switching positions, reducing defocusing effects and optimizing the illumination process.
Implementation Method 1
the optical element comprises an elastically deformable facet portion having a light-reflecting optically effective surface, and at least one actuating element for introducing a bending moment into the facet portion in order to deform the facet portion in such a way as to change a radius of curvature of the optically effective surface
Data Source
AI summary
A field facet system for a lithography apparatus comprises: an optical element which comprises an elastically deformable facet portion having a light-reflecting optically active surface; and at least one actuating element for introducing a bending moment into the facet portion to deform the facet portion to change a radius of curvature of the optically active surface. The facet portion is curved in an arched manner in a plan view of the optically active surface. The rigidity of the facet portion as viewed along a longitudinal direction of the facet portion is variable so that a normal vector oriented perpendicularly to the optically active surface tilts exclusively about a spatial direction when the bending moment is introduced into the facet portion.