Laser-Etched EUV Mirror Channels for Stable Cooling
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Solution Overview
Problem
EUV lithography systems face challenges in efficient cooling due to inhomogeneous thermal expansion and flow-induced vibrations caused by angular and rough cooling channels, leading to potential mechanical damage and image aberrations.
Innovation Solution
The development of optical elements with channels that maintain a consistent cross-sectional area and distance from the reflective coating, produced using selective laser-induced etching, to ensure efficient cooling and minimize flow-induced vibrations, utilizing titanium-doped fused silica substrates with controlled thermal properties and optimized channel geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling channels are milled into the substrate, then cooling efficiency is improved, but flow-induced vibrations and image aberrations occur due to angular and rough channel surfaces
Solution Approach 1:
The patent replaces mechanical milling with laser-induced etching to create cooling channels. This substitution eliminates the mechanical contact that causes angular and rough surfaces, thereby reducing flow-induced vibrations while maintaining effective cooling.
Solution Approach 2:
The patent changes the surface parameters of the cooling channels by using laser etching instead of mechanical milling. This results in smoother channel surfaces with different roughness characteristics, reducing turbulence and vibrations caused by coolant flow.
2Ease of manufacture
If conventional milling is used to create cooling channels, then production is simpler, but channel cross-section varies and causes inhomogeneous cooling
Solution Approach 1:
The patent replaces mechanical milling with laser-induced etching, which allows for precise control of channel geometry. This enables consistent cross-sectional areas throughout the channel length, ensuring homogeneous cooling despite the increased manufacturing complexity.
Solution Approach 2:
The patent changes the manufacturing process parameters by using laser etching with controlled focal depth and scanning patterns. This enables precise control over channel cross-sectional dimensions, maintaining consistency throughout the channel length while achieving the required cooling performance.
3Temperature
If channels are introduced into the substrate, then cooling capability is improved, but thermal expansion inhomogeneity causes shape changes
Solution Approach 1:
The patent applies local quality by creating specifically positioned and dimensioned cooling channels at controlled distances from the reflective coating. This localized cooling approach addresses thermal hot spots while minimizing overall thermal gradients that cause shape changes.
Solution Approach 2:
The patent changes the thermal parameters of the substrate by introducing controlled cooling channels with specific geometric parameters. The consistent cross-sectional area and optimized positioning create more uniform heat distribution, reducing thermal expansion inhomogeneity and associated shape changes.
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 enables efficient cooling of EUV radiation mirrors with reduced thermal gradients and flow-induced vibrations, maintaining the optical element's stability and image quality.
Implementation Method 1
the coefficient of thermal expansion differs significantly from zero away from the zero-crossing temperature
Implementation Method 2
a cooling fluid flows through the channel
Data Source
AI summary
An optical element reflects radiation, such as EUV radiation. The optical element includes a substrate with a surface to which a reflective coating is applied. The substrate has at least one channel through which a coolant can flow. The substrate is formed from fused silica, such as titanium-doped fused silica, or a glass ceramic. The channel has a length of at least 10 cm below the surface to which the reflective coating is applied. The cross-sectional area of the channel varies by no more than +/â20% over the length of the channel.