Radiational Cooling for EUV Mirror Temperature Control
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Solution Overview
Problem
In EUV microlithography, maintaining a constant temperature of optical mirrors is challenging due to residual absorption of light, which causes thermal expansion and optical property changes, and traditional cooling methods introduce vibrations and mechanical stress.
Innovation Solution
A device with a radiational cooling part and a heating part, using a heat sink with controllable temperature and resistance wires for direct or indirect heating, allows for flexible temperature control, minimizing thermal expansion and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If water cooling of mirror substrate is used, then thermal load is reduced, but dynamic excitation of structural eigen-modes occurs causing vibrations
Solution Approach 1:
The patent replaces the mechanical water cooling system with a radiational cooling system. Instead of using water flowing through channels and tubes that mechanically excites structural eigen-modes, the invention uses a radiational cooling part that cools the mirror substrate through radiation heat transfer without mechanical contact or fluid flow, thereby eliminating vibrations while still reducing thermal load
Solution Approach 2:
The patent introduces a radiational cooling part as an intermediary between the mirror substrate and the cooling function. This intermediary component enables heat removal through radiation rather than through mechanical fluid coupling, serving as a mediator that achieves cooling without the harmful mechanical excitation of water cooling systems
2Manufacturing precision
If mirror holding structure is optimized for minimum parasitic forces, then surface figure stability is improved, but thermal conduction capability is reduced
Solution Approach 1:
The patent introduces a radiational cooling part as an intermediary thermal management component that does not require mechanical coupling to the mirror substrate. This allows the holding structure to be optimized for minimum parasitic forces without compromising thermal management, as the radiational cooling system provides an alternative thermal conduction path independent of the mechanical holding structure
Solution Approach 2:
The patent separates the functions of mechanical support and thermal management into independent components. The holding structure is optimized purely for mechanical support with minimum parasitic forces, while the radiational cooling part handles thermal management separately through radiation heat transfer, eliminating the need for the holding structure to provide both functions
3Loss of energy
If reflective coatings with high reflectivity are used, then light absorption is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent converts the harmful effect of residual light absorption into a beneficial thermal management opportunity. Instead of trying to eliminate all absorption through increasingly complex high-reflectivity coatings, the invention accepts the residual absorption and uses it as a heat source for a controlled radiational cooling system, thereby managing the thermal load without requiring near-perfect reflectivity coatings
Solution Approach 2:
The patent changes the approach from optimizing optical parameters (reflectivity) to managing thermal parameters (radiational cooling). By shifting the focus from maximizing reflectivity to actively managing the thermal load through radiational cooling, the system achieves effective thermal control without requiring manufacturing extremely high-reflectivity coatings
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 maintains a stable temperature profile, reducing wave-front errors and thermal drift, and is effective in ultra-high vacuum environments without mechanical stress, enhancing the performance of EUV microlithography tools.
Implementation Method 1
at least one heat sink (20) to receive thermal radiation from a mirror heat transfer area (18) of the optical mirror (17)
Implementation Method 2
a heating device (22) to heat the mirror heat transfer area (18)
Implementation Method 3
a portion of light hitting a mirror surface will be absorbed by the optical coating and/or the mirror substrate underneath. This absorbed radiant power in turn heats up the mirror substrates
Data Source
AI summary
A device serves for controlling temperature of an optical element provided in vacuum atmosphere. The device has a cooling apparatus having a radiational cooling part, arranged apart from the optical element, for cooling the optical element by radiation heat transfer. A controller serves for controlling temperature of the radiational cooling part. Further, the device comprises a heating part for heating the optical element. The heating part is connected to the controller for controlling the temperature of the heating part. The resulting device for controlling temperature in particular can be used with an optical element in a EUV microlithography tool leading to a stable performance of its optics.