EUV Catoptric Optical Unit Chief Ray Plane Geometry
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Solution Overview
Problem
Existing imaging catoptric EUV projection optical units face bothersome polarization influences due to large illumination angles and high numerical apertures, leading to aberrations and imaging quality issues.
Innovation Solution
The design incorporates chief ray planes with angles differing from 0, allowing the chief ray of the central object field point to propagate through multiple planes, which compensates for polarization influences by preferring tangential polarization over radial polarization, thereby reducing diattenuation and maintaining imaging quality across the image field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large illumination angles and high numerical apertures are used to increase imaging capability, then imaging quality and resolution are improved, but polarization influences and diattenuation increase causing aberrations
Solution Approach 1:
The patent introduces a third dimension by allowing the chief ray to propagate through multiple chief ray planes (different angular dimensions) rather than confined to a single plane. This multi-planar propagation compensates for polarization influences by averaging out the diattenuation effects that occur at different angles of incidence, thereby maintaining imaging quality at high numerical apertures
Solution Approach 2:
The patent changes the angular parameters of ray propagation by designing mirrors with specific orientations and curvatures that enable the chief ray to traverse multiple planes with different incidence angles. This parameter variation compensates for the polarization-dependent reflectivity variations, reducing overall diattenuation while preserving the high numerical aperture capability
2Manufacturing precision
If high numerical aperture is used to improve resolution, then imaging resolution is improved, but diattenuation increases causing imaging aberrations
Solution Approach 1:
By extending ray propagation into multiple chief ray planes, the system achieves high numerical aperture (improving resolution) while the multi-planar geometry naturally averages out polarization effects, maintaining consistent imaging quality across the field without excessive diattenuation
3Productivity
If large image field area is used to increase productivity, then production area is improved, but polarization influences increase causing quality issues
Solution Approach 1:
The multi-chief-ray-plane architecture allows the optical system to cover a large image field area while maintaining consistent ray propagation geometry across the field. This geometric consistency compensates for polarization influences even at the edges of large fields, enabling high productivity without quality degradation
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 approach effectively minimizes diattenuation, ensuring imaging with aberrations smaller than prescribed values across a large image field, even at high numerical apertures and illumination angles, thereby enhancing the imaging quality and reducing polarization-related issues.
Implementation Method 1
compensate polarization influences on the mirror reflectivity, which generally differ firstly perpendicular and secondly parallel to the plane of incidence on the respective mirror
Implementation Method 2
Bothersome polarization influences, which can be reduced by the optical unit according to the invention, can emerge as a result of large illumination angles as a result of large image field-side numerical apertures of the imaging optical unit. Bothersome polarization influences can emerge during the reflection of imaging light at the mirrors of the optical unit
Data Source
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AI summary
An imaging catoptric optical unit (7) has at least four mirrors (Ml to M4), which image an object field (4) in an object plane (5) into an image field (8) in an image plane (9). A first chief ray plane (yz) of the optical unit is prescribed by propagation of a chief ray (16) of a central object field point during the reflection at one of the mirrors (Ml). A second chief ray plane (xz) of the optical unit is prescribed by propagation of the chief ray (16) of the central object field point during the reflection at one of the other mirrors (M3, M4). The two chief ray planes (yz, xz) include an angle that differs from 0. In an alternative or additional aspect, the imaging optical unit (7), considered via the image field (8), has a maximum diattenuation (D) of 10% or a diattenuation that prefers a tangential polarization of the imaging light for a respectively considered illumination angle. The result of both aspects is an imaging optical unit in which bothersome polarization influences are reduced during the reflection of imaging light at the mirrors of the imaging optical unit.