Penultimate Mirror Design for EUV Imaging Optical Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Imaging optical systems with pupil obscuration face challenges in maintaining high light throughput and minimizing imaging errors while managing production complexity, particularly when using thin mirror bodies and small wavelength light sources.
Innovation Solution
Configuring the penultimate mirror with a continuous reflective face and optimizing the pupil obscuration to less than 5% allows for adequate mirror thickness and spacing, enabling high light throughput and minimal imaging quality impact, while using free-form mirror faces and multiple intermediate images for error correction and compact system design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the penultimate mirror is configured with a through-opening to enable beam passage, then the light throughput is improved, but the manufacturing complexity increases and the mirror structural stability deteriorates
Solution Approach 1:
The patent extracts the beam passage function from the mirror structure by introducing a separate beam passage component that guides light around the mirror, eliminating the need for a through-opening in the mirror itself. This allows the mirror to maintain its structural integrity while still enabling light transmission through the optical system.
Solution Approach 2:
The patent introduces an intermediary beam passage structure that mediates between the mirror and the light beam, allowing light to pass through the optical system without requiring modifications to the mirror structure. This intermediary component resolves the conflict between maintaining mirror integrity and enabling light transmission.
2Ease of manufacture
If the pupil obscuration is increased to simplify mirror design, then the manufacturing ease is improved, but the light throughput decreases
Solution Approach 1:
The patent resolves the contradiction by transitioning from a two-dimensional mirror surface design to a three-dimensional spatial arrangement where the beam passage component guides light in a different spatial dimension, allowing full light throughput while maintaining simple mirror design.
Solution Approach 2:
The patent segments the optical path into distinct functional zones: the mirror handles reflection while the separate beam passage component handles light transmission. This segmentation allows each component to be optimized independently, maintaining both manufacturing simplicity and light throughput.
3Volume of moving object
If the spacing between the penultimate mirror and image plane is reduced to compact the system, then the system size is decreased, but the manufacturing precision requirements increase
Solution Approach 1:
The patent employs curved or free-form mirror surfaces that can achieve the required optical transformation within a shorter axial distance, allowing system compactification without proportionally increasing precision requirements. The curvature enables more efficient light path folding.
Solution Approach 2:
The patent optimizes various optical parameters including numerical aperture, focal lengths, and beam angles to enable a more compact configuration. By carefully selecting and adjusting these parameters, the system achieves compactness while keeping manufacturing precision within feasible limits.
4Measurement precision
If free-form mirror faces are used to correct imaging errors, then the imaging precision is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent applies free-form surface design and optimization algorithms during the design phase to pre-correct for manufacturing tolerances and anticipated errors. This preliminary optimization reduces the actual manufacturing precision requirements while maintaining final imaging quality.
Solution Approach 2:
The patent implements free-form surfaces only in critical regions where they provide maximum imaging error correction benefit, while other regions use simpler spherical or aspherical surfaces. This localized application of complexity reduces overall manufacturing difficulty while maintaining imaging precision.
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 achieves high light throughput with minimal imaging quality degradation, facilitating the production of microstructured or nanostructured components with improved resolution and compact system design, suitable for EUV and other small wavelength applications.
Implementation Method 1
an imaging optical system with six mirrors (M1 to M6), which have free-form reflection faces
Data Source
AI summary
An imaging optical system has a plurality of mirrors which image an object field in an object plane in an image field in an image plane. The imaging optical system has a pupil obscuration. The last mirror in the beam path of the imaging light between the object field and the image field has a through-opening for the passage of the imaging light. A penultimate mirror of the imaging optical system in the beam path of the imaging light between the object field and the image field has no through-opening for the passage of the imaging light. The result is an imaging optical system that provides a combination of small imaging errors, manageable production and a good throughput for the imaging light.