EUV Projection Optical System Polarization Arrangement
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Solution Overview
Problem
Optical systems for EUV microlithography face challenges in minimizing undesired shadings, improving mechanical and thermal stability, simplifying production, reducing beam offset, and enabling both polarized and unpolarized operations with unchanged light distribution and higher transmission.
Innovation Solution
The optical system incorporates a polarization-influencing arrangement with strategically chosen distances between reflection surfaces, allowing for reduced shadings, improved stability, and cost-effective production, featuring double reflection surface units with closely spaced and angled reflection surfaces that maintain light distribution consistency when the polarization-influencing arrangement is removed or introduced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polarization-influencing arrangement with two reflections at the Brewster angle is used to polarize incident light, then linear polarization is achieved, but undesired shadings are introduced in the beam path
Solution Approach 1:
The patent transitions from a planar arrangement of reflection surfaces to a three-dimensional configuration where multiple reflection surfaces are arranged at different heights and angles. This spatial dimensionality change allows the polarizing function to be achieved while the reflected beams are directed to different spatial locations, preventing overlapping shadings in the beam path.
Solution Approach 2:
The polarization function is divided into multiple independent reflection surface units, each contributing to the overall polarization effect. By segmenting the single polarizing element into multiple smaller reflection surfaces arranged in series, the patent achieves polarization while distributing the optical paths to minimize shading interference.
2Adaptability or versatility
If multiple individual mirrors are arranged parallel next to one another to achieve polarization, then the polarization direction can be set individually, but the mechanical mounting becomes complex and thermal stability is reduced
Solution Approach 1:
Multiple reflection surfaces that would traditionally require separate mechanical mountings are merged into a single integrated component structure. The patent combines multiple reflection surfaces onto one substrate or housing, reducing the number of individual mountings from multiple separate mirror assemblies to a unified mechanical structure, thereby simplifying installation and improving thermal stability.
Solution Approach 2:
The single component housing multiple reflection surfaces serves multiple functions simultaneously: it provides the polarizing function, maintains fixed angular relationships between surfaces, and provides a unified mechanical mounting interface. This multi-functionality eliminates the need for separate adjustment mechanisms for each mirror while preserving the ability to set polarization direction.
3Loss of energy
If the polarization-influencing arrangement is removed to enable unpolarized operation, then higher transmission is achieved, but the light distribution in the optical system changes
Solution Approach 1:
The patent introduces a controllable element (such as a movable mirror or shutter) that acts as an intermediary to selectively block or redirect the polarizing reflection paths. When unpolarized operation is desired, this intermediary element redirects the light to bypass the polarizing reflections, maintaining the original light distribution while eliminating the polarization effect and associated losses.
4Object-affected harmful factors
If the distance between reflection surfaces is reduced to minimize shadings, then beam offset is minimized, but mechanical precision requirements increase
Solution Approach 1:
The patent employs asymmetric arrangement of reflection surfaces where the distances between consecutive surfaces are not equal. By strategically designing unequal spacing between reflection surfaces, the patent minimizes beam offset through geometric compensation while the asymmetric structure itself provides inherent mechanical stability that reduces sensitivity to small dimensional variations.
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 reduces shadings and beam offset, enhances mechanical and thermal stability, and allows for higher transmission during polarized operation while enabling seamless transitions between polarized and unpolarized modes without altering light distribution.
Implementation Method 1
light incident on the first reflection surfaces forms an angle of 43°±10°, in particular 43°±5°, with the first reflection surfaces
Implementation Method 2
light incident on the first reflection surface of the first double reflection surface unit is reflected toward the second reflection surface of the second double reflection surface unit
Data Source
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AI summary
The invention relates to an optical system for a microlithographic projection exposure apparatus for operation in the EUV. The optical system comprises at least one polarization-influencing arrangement (124, 224, 324, 424, 524, 624, 724) having at least one first and one second double reflection surface unit (128, 228, 328, 428, 528, 728). The double reflection surface units each have a first reflection surface (128.1, 228.1, 328.1, 428.1, 528.1) and a second reflection surface (128.2, 228.2, 328.2, 428.2, 528.2). Within the same double reflection surface unit, in each case the first reflection surface and the second reflection surface are arranged directly adjacent at a distance d1 and at an angle of 0°±10° relative to one another. The first reflection surface of the first double reflection surface unit and the second reflection surface of the second double reflection surface unit are arranged directly adjacent at a distance d2 and at an angle of 0°±10° relative to one another. During operation of the optical system, light (125, 225, 325, 425, 525) incident on the first reflection surfaces forms an angle of 43°±10°, in particular 43°±5°, with the first reflection surfaces. During operation of the optical system, light incident on the first reflection surface of the first double reflection surface unit is reflected toward the second reflection surface of the second double reflection surface unit. For the distances d1 and d2 it holds true that: d2 > 5 ∗ d1.