Compact Four-Mirror Imaging Optical Unit for Metrology
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing magnifying imaging optical units for microlithography and metrology systems are not compact enough and lack efficient aberration correction, leading to suboptimal performance in terms of size and resolution.
Innovation Solution
A compact imaging optical unit with a structural length to imaging scale ratio of less than 4.9 mm, utilizing four mirrors with a convex fourth mirror and aspherical first to third mirrors for aberration correction, and optionally two intermediate image planes, allowing for a compact configuration and high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional magnifying imaging optical unit is used, then the imaging function is provided, but the structural length is too large and the unit is not compact
Solution Approach 1:
The patent employs multiple intermediate image planes arranged in a folded optical path configuration, transforming a linear optical path into a multi-dimensional arrangement. This allows the imaging optical unit to achieve high magnification while maintaining a compact overall structure by utilizing spatial folding rather than linear extension.
Solution Approach 2:
The imaging optical unit is divided into multiple stages with intermediate image planes positioned between object and final image fields. This segmentation allows each stage to contribute to the overall magnification while keeping individual component sizes small, achieving compactness through modular arrangement.
2Manufacturing precision
If conventional mirrors are used for imaging, then the basic imaging function is achieved, but aberration correction is insufficient
Solution Approach 1:
Different mirrors in the optical path are assigned different shapes (spherical or aspherical) based on their specific functional requirements. Aspherical mirrors are used where higher aberration correction is needed, while spherical mirrors are used where simpler geometry suffices, optimizing the balance between correction performance and manufacturing complexity.
Solution Approach 2:
The patent utilizes both spherical and aspherical mirror surfaces to correct optical aberrations. The aspherical mirrors provide enhanced aberration correction capability while maintaining a reflective optical path, achieving high imaging precision without requiring complex refractive elements.
3Measurement precision
If the imaging scale is increased to improve resolution, then measurement precision improves, but the structural length increases
Solution Approach 1:
The optical path is folded multiple times through intermediate image planes, creating a compact three-dimensional arrangement that achieves high magnification ratios without requiring long linear paths. This dimensional folding allows high resolution to be achieved within a small overall footprint.
Solution Approach 2:
The intermediate image planes are nested within the folded optical path structure, allowing multiple imaging stages to be contained within a compact volume. This nested arrangement enables high imaging scale while maintaining small structural dimensions.
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 results in a highly compact and efficient imaging optical unit with improved aberration correction, suitable for high-resolution metrology and inspection systems, particularly in EUV microlithography, with enhanced light throughput and reduced accuracy requirements.
Implementation Method 1
at least four mirrors to image an object field in an object plane into an image field in an image plane
Data Source
AI summary
An imaging optical unit includes at least four mirrors to image an object field in an object plane into an image field in an image plane. The ratio of the structural length of the imaging optical unit to the imaging scale of the imaging optical unit is less than 4.9 mm. The imaging optical unit provides improved handling properties, such as, for example, when used in a metrology system.