EUV Illumination Optic Light Trap for Stray Light Suppression
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Solution Overview
Problem
Current illumination optical units for EUV projection lithography face challenges in suppressing extraneous light without causing unwanted thermal or optical effects, such as stray light, which can interfere with imaging quality and system accuracy.
Innovation Solution
The illumination optical unit incorporates a second facet mirror with an illumination light trap portion, featuring a conically inclined reflection surface or absorbing material, strategically positioned to dissipate extraneous light components away from the beam path, utilizing thermal coupling with a heat sink for efficient energy dissipation and minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If extraneous light is suppressed using conventional methods, then imaging quality deteriorates due to unwanted thermal or optical effects, but light suppression is insufficient
Solution Approach 1:
The patent extracts and removes extraneous light from the optical system using an illumination light trap portion positioned at a distance greater than the maximum angle facets from the facet arrangement center. This trap portion selectively captures and dissipates unwanted light components before they can generate harmful thermal or optical effects, while preserving the useful illumination light for imaging.
Solution Approach 2:
The illumination light trap portion acts as an intermediary element between the extraneous light and the imaging system. It provides a controlled pathway for dissipating unwanted light through thermal coupling with a heat sink, preventing direct interaction between extraneous light and sensitive optical components, thereby eliminating harmful thermal and optical effects.
2Device complexity
If illumination light trap portion is positioned closer to facet arrangement center, then device complexity is reduced, but imaging quality deteriorates due to interference from dissipated light
Solution Approach 1:
The patent applies local quality by positioning the illumination light trap portion at a specific location where its distance from the facet arrangement center is greater than the distance of the maximum angle facets. This strategic positioning ensures that the trap portion only affects extraneous light while leaving the useful illumination light unaffected, thereby maintaining high imaging quality without excessive structural complexity.
3Manufacturing precision
If illumination light trap portion is positioned farther from facet arrangement center, then imaging quality is improved by reducing interference, but device complexity increases
Solution Approach 1:
The patent resolves the complexity issue by utilizing the spatial dimension - positioning the illumination light trap portion in a location that is radially farther from the facet arrangement center than the maximum angle facets. This dimensional arrangement allows the trap to be integrated into the existing optical path without adding significant structural complexity, while effectively improving imaging quality by preventing interference from dissipated light.
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 solution effectively suppresses unwanted thermal and optical effects, enhancing imaging quality, correcting system errors, and optimizing illumination distribution by controlled dissipation of extraneous light, thereby improving the overall performance of EUV projection lithography systems.
Implementation Method 1
The second mirror carrier has an illumination light trap portion, the distance of which from the facet arrangement center is greater than a distance of the second maximum angle facets from the facet arrangement center. The illumination light trap portion has at least one reflection surface that is inclined in relation to a carrier plane of the second mirror carrier.
Implementation Method 2
utilizing thermal coupling with a heat sink for efficient energy dissipation
Implementation Method 3
The illumination light trap portion has at least one reflection surface that is inclined in relation to a carrier plane of the second mirror carrier. The reflection surface of the illumination light trap portion is arranged conically around the facet arrangement center.
Data Source
AI summary
An illumination optical unit for EUV projection lithography illuminates an object field with illumination light. The illumination optical unit has a first facet mirror including a plurality of first facets on a first mirror carrier. Disposed downstream of the first facet mirror is a second facet mirror including a plurality of second facets arranged on a second mirror carrier around a facet arrangement center. Partial beams of the illumination light are guided superposed on one another into the object field, respectively via illumination channels which have one of the first facets and one of the second facets. Second maximum angle facets are arranged at the edge of the second mirror carrier. The second maximum angle facets predetermine maximum illumination angles of the illumination light which deviate maximally from a chief ray incidence on the object field.