EUV Optical Element Degradation Prediction and Decontamination
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Solution Overview
Problem
Optical elements in EUV lithography projection exposure apparatuses face degradation due to chemical reactions with residual gases, leading to reduced reflectivity and operational issues, which existing methods fail to address effectively.
Innovation Solution
A method involving the determination of degradation profiles, prediction of future degradation, and targeted feeding of decontamination media, such as hydrogen or oxygen, to maintain optical element performance by monitoring deviations from pre-defined limit values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the optical element is operated in a vacuum environment with residual gas atmosphere, then the EUV radiation can reach the optical element, but chemical reactions occur between the reflective coating layers and residual gases leading to degradation
Solution Approach 1:
The patent applies composite materials by creating a multilayer reflective coating system consisting of alternating high-refractive-index layers (e.g., molybdenum, ruthenium) and low-refractive-index layers (e.g., silicon, silicon oxide). This composite structure optimizes EUV reflectivity while the outermost layer provides chemical stability against residual gas reactions, thus resolving the contradiction between radiation transmission and coating stability.
Solution Approach 2:
The patent implements an inert environment strategy by maintaining ultra-high vacuum conditions in the projection exposure apparatus and using an inert gas atmosphere (e.g., nitrogen or rare gases) in the storage and transport environment. This prevents chemical reactions between the reflective coating and reactive residual gases, thereby protecting the coating stability while allowing EUV operation when needed.
2Reliability
If a capping layer is applied to protect against degradation, then the reflective coating is protected, but the capping layer itself is subject to degradation such as oxidation
Solution Approach 1:
The patent uses composite materials by designing a multilayer capping structure where the outermost layer consists of highly oxidation-resistant materials such as platinum, palladium, or iridium. These materials form a stable protective barrier that prevents oxidation of inner layers while maintaining long-term stability in the vacuum environment, thus extending the capping layer lifespan.
Solution Approach 2:
The patent applies the disposable principle by designing the capping layer as a sacrificial protective element that can be easily replaced. The capping layer is intentionally made as a separate, replaceable component that protects the expensive multilayer reflective coating during operation and can be renewed when degradation occurs, extending the overall system lifespan.
3Reliability
If degradation monitoring is performed continuously, then future degradation can be predicted, but the system complexity increases
Solution Approach 1:
The patent implements feedback by continuously monitoring optical parameters (reflectivity, transmission) of the optical element and using this information to predict future degradation states. The monitoring system provides real-time feedback to the control unit, which adjusts operational parameters or triggers maintenance alerts when degradation thresholds are approached, enabling predictive maintenance without excessive system complexity.
Solution Approach 2:
The patent replaces complex mechanical monitoring systems with optical measurement methods. Instead of physical inspection or contact-based sensing, the system uses non-contact optical measurements of reflectivity and transmission to monitor degradation, significantly reducing system complexity while maintaining high prediction accuracy.
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 allows for early identification and mitigation of critical degradation states, ensuring reliable and efficient operation of optical elements by regulating their degradation and extending their lifespan.
Implementation Method 1
the chemical reaction is initiated or at least fostered by the EUV radiation
Implementation Method 2
such a capping layer may also be subject to a degradation, for example an oxidation
Implementation Method 3
feeding of a first decontamination medium (in particular a reducing medium) into the interior
Data Source
AI summary
Method for avoiding a degradation of an optical element, wherein the optical element is arranged in a housing, comprising: a) determining a first degradation value; b) determining a second degradation value, wherein the first degradation value and the second degradation value are determined at different times; c) forming a degradation profile based on the first degradation value and the second degradation value; d) calculating a temporal development of the degradation profile; e) determining at least one predicted degradation value based on the calculated temporal development of the degradation profile; f) comparing the at least one predicted degradation value with a predefinable first limit degradation value; g) monitoring for a predefinable first deviation between the at least one predicted degradation value and the first limit degradation value; h) feeding a first decontamination medium into the interior if attainment of the predefinable first deviation is identified.