EUV Optical Element Lifetime Extension via Capping Layer and Mitigation Gas
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Solution Overview
Problem
The reflectivity of optical elements in EUV radiation systems degrades over time due to exposure to high-energy ions, target material contamination, and localized heating in the vacuum environment, leading to reduced operational lifetime.
Innovation Solution
A reflective optical element with a capping layer made of an insulator, such as a nitride or oxide, is used, and a gas control system introduces a mitigation gas like oxygen or nitrogen to stabilize the capping layer and reduce contamination, enhancing the reflectivity and operational lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical element is placed within the vacuum chamber with the plasma to collect and redirect EUV radiation, then the radiation collection and direction function is achieved, but the reflectivity of the optical element degrades over time due to contamination and damage from high energy ions and target material particles
Solution Approach 1:
A capping layer is introduced as an intermediary protective element between the target material plasma environment and the underlying multilayer mirror structure. This capping layer absorbs the harmful effects of ion bombardment and material deposition, serving as a sacrificial barrier that protects the critical reflective surfaces while allowing the optical element to continue functioning in the harsh vacuum plasma environment
Solution Approach 2:
The patent modifies the chemical and physical parameters of the optical element surface by applying a capping layer with specific material properties (different from the underlying mirror layers). This parameter change creates a surface that is more resistant to contamination and ion damage, fundamentally altering how the optical element interacts with the plasma environment to extend its operational lifetime
2Duration of action of stationary object
If a capping layer is placed on the optical element to protect the surface, then the reflectivity is maintained and lifetime is extended, but the device complexity increases due to additional layers and gas control systems
Solution Approach 1:
The optical element is segmented into distinct functional layers: the underlying multilayer mirror structure for radiation reflection and the outer capping layer for environmental protection. This segmentation allows each layer to be optimized for its specific function while simplifying the overall design approach - the capping layer handles contamination and ion damage, allowing the mirror layers to focus solely on reflectivity
3Object-affected harmful factors
If hydrogen gas is introduced to clean the surface of target material deposits, then contamination is reduced, but hydrogen radicals may recombine on the capping layer surface reducing cleaning effectiveness
Solution Approach 1:
The patent changes the surface parameters of the capping layer to have low hydrogen recombination characteristics. By selecting materials and controlling deposition conditions to achieve this property, the capping layer surface allows hydrogen radicals to remain available for cleaning target material deposits rather than being consumed by recombination, thereby maintaining effective contamination removal
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 solution effectively prolongs the operational lifetime of the reflective optical elements by reducing contamination and maintaining reflectivity through controlled gas introduction, addressing the degradation issues in EUV radiation systems.
Implementation Method 1
a gas control system for controlling the gas distribution system, the gas control system having a state in which the mitigation gas from the source of gas is introduced into the interior of the vacuum chamber in a regulated manner by the gas distribution system
Implementation Method 2
An optical element within the environment may be exposed to high energy ions or particles of target material which can contaminate the optical element's exposed surface
Data Source
AI summary
Degradation of the reflectivity of one or more reflective optical elements in a system for generating EUV radiation is reduced by the controlled introduction of a gas into a vacuum chamber containing the optical element. The gas may be added to the flow of another gas such as hydrogen or alternated with the introduction of hydrogen radicals.