Microlithography Mirror System with Pupil Obscuration Control
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Solution Overview
Problem
Imaging optical systems with multiple mirrors face challenges in achieving a favorable combination of small imaging errors, manageable production, and high throughput, particularly due to pupil obscuration issues that affect imaging quality and light throughput.
Innovation Solution
The design incorporates a pupil-obscured system with a penultimate mirror having a continuous reflective face and a small pupil obscuration, allowing for adequate mirror thickness and spacing, along with free-form mirror surfaces and optimized coating configurations to minimize imaging errors and maximize light throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a through-opening is introduced in the penultimate mirror to reduce pupil obscuration, then light throughput is improved, but the mirror structure becomes more complex and manufacturing difficulty increases
Solution Approach 1:
The patent extracts the pupil obscuration problem by introducing a through-opening in the penultimate mirror, removing the blocking portion that causes light loss. This directly addresses the contradiction by taking out the harmful element (obscuration) while accepting the trade-off of increased manufacturing complexity for the mirror structure.
Solution Approach 2:
The mirror is segmented into different functional zones: the through-opening region that allows light passage and the remaining reflective surface that performs imaging. This segmentation enables the system to simultaneously achieve high light throughput through the opening and maintain imaging functionality on the reflective portions.
2Strength
If mirror thickness is increased to improve structural stability, then mechanical strength is improved, but the spacing between the mirror and image plane must be increased, affecting system compactness
Solution Approach 1:
The patent optimizes the mirror thickness parameter to achieve the minimum required structural strength while minimizing the increase in spacing to the image plane. By carefully controlling this parameter, the system balances mechanical strength requirements with system compactness, avoiding excessive spacing that would affect the overall installation footprint.
3Manufacturing precision
If free-form mirror surfaces are used to correct imaging errors, then imaging precision is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies free-form surfaces with locally optimized quality characteristics to specific mirror regions where they are most effective for correcting imaging errors. Rather than requiring uniform high precision across the entire mirror, the free-form design allows different local zones to have tailored surface properties, improving imaging precision while managing overall manufacturing complexity.
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
This configuration results in a high-resolution imaging optical system with low pupil obscuration, maintaining imaging quality and enabling efficient production of microstructured or nanostructured components in projection exposure installations.
Implementation Method 1
an imaging optical system with a plurality of mirrors which image an object field in an object plane into an image field in an image plane
Data Source
AI summary
An imaging optical system has a plurality of mirrors which image an object field in an object plane into 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 imaging optical system has precisely eight mirrors. The result is an imaging optical system which exhibits a favorable combination of small imaging errors, manageable production and good throughput.