Structured Surface Thermal Accommodation in EUV Lithography
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Solution Overview
Problem
Lithographic apparatuses face challenges in efficiently transferring heat within vacuum environments, leading to thermal expansion issues that affect pattern accuracy, particularly when using extreme ultraviolet (EUV) radiation, where conventional surfaces have limited thermal accommodation coefficients.
Innovation Solution
The introduction of a structured surface with a repeating pattern on components like projection system walls and substrate tables, which increases the effective thermal accommodation coefficient by enhancing heat exchange, reducing thermal expansion and improving pattern overlay accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional smooth surfaces are used in vacuum environment, then manufacturing is simple, but thermal accommodation coefficient is low leading to poor heat transfer
Solution Approach 1:
The patent transforms a two-dimensional smooth surface into a three-dimensional structured surface by adding vertical features (ridges, pillars, or holes) with heights of 1-10 micrometers. This dimensional transformation increases the effective surface area and creates multiple interaction points for gas molecules, thereby enhancing the thermal accommodation coefficient from typical values of 0.1-0.3 to 0.5-0.8 without fundamentally changing the base material or manufacturing process flow.
Solution Approach 2:
The patent employs porous or micro-structured surface topologies including arrays of holes, ridges, and pillars that create a porous-like structure in the surface layer. These structures trap gas molecules through multiple collisions and increase the effective surface area for heat exchange, achieving high thermal accommodation coefficients while maintaining structural integrity and optical performance in the EUV lithography vacuum environment.
2Loss of energy
If structured surfaces are introduced to increase thermal accommodation coefficient, then heat transfer improves, but manufacturing complexity increases
Solution Approach 1:
The patent segments the continuous surface into discrete structural elements (individual ridges, pillars, or holes arranged in patterns) that can be independently formed and optimized. This segmentation allows the use of standard lithographic patterning techniques and modular manufacturing approaches, making the complex surface structures manufacturable using existing EUV lithography tooling and processes rather than requiring entirely new manufacturing methods.
3Area of stationary object
If surface area is increased through structuring, then thermal accommodation coefficient increases, but component geometry becomes more complex
Solution Approach 1:
The patent optimizes the geometric parameters of the surface structures (height, width, spacing, and patterns of ridges, pillars, or holes) to dynamically adapt to different thermal management requirements and optical path constraints. The structures are designed with aspect ratios and dimensions that can be adjusted based on the specific component location and thermal load, allowing optimization of both surface area and geometric simplicity for each application.
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
The structured surfaces effectively increase heat transfer from gas to the projection system components, reducing thermal expansion and enhancing the accuracy of pattern overlay on substrates during EUV lithography.
Implementation Method 1
a surface of a component of the lithographic apparatus which is in a vacuum environment in use is provided with a repeating structure which is configured to increase the effective thermal accommodation coefficient of the surface
Data Source
AI summary
A lithographic apparatus includes a substrate table constructed to hold a substrate, and a projection system configured to project a patterned radiation beam onto a target portion of the substrate. A surface of a component of the lithographic apparatus that is in a vacuum environment in use is provided with a repeating structure configured to increase the effective thermal accommodation coefficient of the surface.