EUVL Optics Protection via Plasma-Induced Carbon Coating
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Solution Overview
Problem
Plasma-facing optics in extreme ultraviolet lithography (EUVL) are degraded by the nearby xenon plasma, leading to erosion, oxidation, and reduced mirror quality, necessitating a protective layer that maintains reflectivity without substantial absorption of EUV radiation.
Innovation Solution
A thin carbon layer is deposited by decomposing a hydrocarbon gas, such as methane, using the xenon plasma in EUVL, which protects the optics from degradation while minimizing reflectivity loss and can be controlled in thickness to prevent excessive absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is deposited on the plasma-facing optics to protect from erosion and oxidation, then the useful life and reliability of the optics is extended, but the reflectivity of the optic is degraded due to absorption by the coating
Solution Approach 1:
The patent applies a thin film coating (carbon layer approximately 1-10 nm thick) on the plasma-facing optics to provide protection while minimizing absorption. The thin film principle allows the coating to be thin enough to maintain reflectivity while still providing adequate protection from plasma-induced erosion and oxidation.
Solution Approach 2:
The patent uses a composite structure consisting of a carbon-based protective layer deposited on the existing Mo/Si multilayer mirror. This composite material approach combines the protective properties of carbon with the high reflectivity properties of the Mo/Si multilayer, achieving both protection and maintained reflectivity.
2Reliability
If the protective layer is made thicker to provide better protection, then the protection effectiveness increases, but the absorption of EUV radiation increases and reflectivity decreases
Solution Approach 1:
The patent carefully controls the thickness parameter of the protective carbon layer, optimizing it to be in the range of approximately 1-10 nm. This parameter optimization ensures the layer is thick enough to provide protection from plasma erosion and oxidation while remaining thin enough to minimize EUV radiation absorption and maintain reflectivity.
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 carbon layer effectively prevents erosion and oxidation of the Si layer, maintaining reflectivity and extending the useful life of the optics, with the ability to monitor and replenish the layer as needed to maintain optimal thickness.
Implementation Method 1
A carbon layer produced by the decomposition of methane can be used to provide a protective layer
Implementation Method 2
interaction of laser beam 30 with the xenon gas creates a plasma that produces the extreme ultraviolet (EUV) radiation
Data Source
AI summary
A coating for the protection of optical surfaces exposed to a high energy erosive plasma. A gas that can be decomposed by the high energy plasma, such as the xenon plasma used for extreme ultraviolet lithography (EUVL), is injected into the EUVL machine. The decomposition products coat the optical surfaces with a protective coating maintained at less than about 100 Å thick by periodic injections of the gas. Gases that can be used include hydrocarbon gases, particularly methane, PH3 and H2S. The use of PH3 and H2S is particularly advantageous since films of the plasma-induced decomposition products S and P cannot grow to greater than 10 Å thick in a vacuum atmosphere such as found in an EUVL machine.