Catalytic Surface Cleaning for EUV Optical Reflectivity
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Solution Overview
Problem
Existing methods for cleaning optical surfaces in EUV irradiation units, such as those using atomic hydrogen, require complex constructions and can cause physical degradation due to localized plasma, as atomic hydrogen recombines quickly and cannot be transported over long distances without loss.
Innovation Solution
Providing catalytic surface regions with a total surface area at least twice that of the optical surface to be cleaned, allowing molecular hydrogen to dissociate into atomic hydrogen without additional radiation or thermal activation, which is then transported to the optical surface for effective cleaning without adding complexity or degrading components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If atomic hydrogen is generated by plasma discharge, microwave discharge, or thermal activation close to the optical surface, then effective cleaning is achieved, but device complexity increases and optical components suffer from accelerated chemical and physical degradation
Solution Approach 1:
The patent introduces molecular hydrogen as an intermediary substance that is transported through the vacuum chamber and dissociated on the optical surface to generate atomic hydrogen in situ. This eliminates the need for complex plasma generation devices close to the optical surface, reducing construction complexity while maintaining cleaning effectiveness
Solution Approach 2:
The patent replaces mechanical/physical plasma generation systems with a chemical approach using molecular hydrogen gas flow. Instead of using plasma discharge or microwave heating devices, the system uses chemical dissociation of H2 molecules on the optical surface to produce atomic hydrogen for cleaning
2Reliability
If atomic hydrogen is generated close to the optical surface, then cleaning effectiveness is improved, but the optical components experience accelerated chemical and physical degradation
Solution Approach 1:
The patent performs preliminary action by introducing molecular hydrogen gas through the vacuum chamber before it reaches the optical surface. The hydrogen is dissociated into atomic hydrogen on the optical surface at the point of use, preventing the harmful effects of localized plasma while ensuring effective cleaning
Solution Approach 2:
Molecular hydrogen acts as an intermediary that carries the cleaning function without the harmful effects. It is dissociated on the optical surface to generate atomic hydrogen only where needed, avoiding the accelerated degradation caused by localized plasma generation
3Device complexity
If molecular hydrogen is used and transported through the vacuum chamber, then device complexity is reduced, but hydrogen recombination and loss occur over larger distances
Solution Approach 1:
The patent changes the parameter of hydrogen transport by using molecular hydrogen gas flow instead of atomic hydrogen. Molecular hydrogen is more stable and can be transported through the vacuum chamber without recombination, maintaining simplicity of construction while minimizing substance loss
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 method enables effective cleaning of optical surfaces in EUV irradiation units without complex constructions, maintaining high optical quality and mechanical stability by ensuring a sufficient concentration of atomic hydrogen reaches the surface, thus preventing debris accumulation and maintaining reflectivity.
Implementation Method 1
The catalytic material is selected to cause dissociation of molecular hydrogen when coming in contact with the second surface region(s)
Implementation Method 2
contaminant or undesirable material being removable or convertible by exposure with atomic hydrogen
Data Source
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Figure 3
AI summary
The present invention relates to a method of cleaning a surface at least partly covered with contaminant or undesired material by applying atomic hydrogen. The invention also proposes an irradiation unit adapted to perform the cleaning method. In the present method the atomic hydrogen is generated by dissociation of molecular hydrogen directed to a surface containing catalytic material, which causes the dissociation of at least a part of the molecular hydrogen to atomic hydrogen. The surface with the catalytic material is arranged close to the surface to be cleaned and is dimensioned such that its total surface area is at least twice the surface area of the to be cleaned surface region. The method allows for the cleaning of the surface region in a constructive simple and efficient manner.