EUV Optical Surface Cleaning via Localized Hydrogen Gas Delivery
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Solution Overview
Problem
In extreme ultraviolet (EUV) optical assemblies maintained in vacuum process chambers, surface contamination from oxidation, carbonaceous growth, and residual gases leads to reduced reflectivity and increased light absorption, necessitating a more effective cleaning method to maintain optimal throughput and uptime.
Innovation Solution
A system that uses remote generation and storage of cleaning gases, such as molecular or atomic hydrogen, delivered through specialized nozzles and guide skirts to restrict gas flow to the immediate vicinity of optical surfaces, minimizing contamination and reducing the need for complex cooling systems and maintenance procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a vacuum process chamber is used to prevent EUV photon absorption, then light transmission is improved, but optical surfaces become contaminated through oxidation and carbonaceous growth
Solution Approach 1:
The patent introduces a controlled inert gas environment (nitrogen or sulfur hexafluoride) around the optical surfaces within the vacuum chamber. This creates a localized protective atmosphere that prevents oxidation and carbonaceous growth on the optical surfaces while maintaining the vacuum conditions necessary for EUV light transmission. The inert gas flow continuously replaces contaminated gas, keeping the optical surfaces clean without requiring the entire chamber to be filled with inert gas.
2Object-affected harmful factors
If cleaning gases are delivered directly to optical surfaces, then surface contamination is reduced, but gas flow requirements increase leading to heat and vibration issues
Solution Approach 1:
The patent implements localized gas delivery through nozzles positioned in close proximity to the optical surfaces. This creates a focused microenvironment of cleaning gas exactly where needed, rather than flooding the entire chamber. The localized approach minimizes the total gas flow requirements, reducing the heat and vibration issues associated with high-velocity gas flows, while still effectively preventing surface contamination.
3Temperature
If complex cooling systems are implemented to manage heat from gas delivery, then temperature control is improved, but device complexity increases
Solution Approach 1:
The patent designs the gas delivery system so that the cleaning gas flow itself serves the dual purpose of both cleaning the optical surfaces and providing cooling. The gas flow absorbs heat from the optical surfaces and surrounding components, carrying it away without requiring separate active cooling systems. This self-service approach reduces device complexity while maintaining effective temperature control.
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 effectively reduces surface contamination, maintains high reflectivity, and simplifies maintenance by reducing heat and vibration impacts, while minimizing gas flow requirements and contamination risks, thereby enhancing EUV optical assembly performance and uptime.
Implementation Method 1
direct a flow of hydrogen gas to a multilayered optical element... the hydrogen reacts with the oxygen to form water molecules
Implementation Method 2
the hydrogen atoms occupy sites on the optical surface to which carbon would otherwise be bindable
Implementation Method 3
highly reflective multilayer coated mirrors (e.g., molybdenum/silicon (Mo/Si) coated mirrors), which function as Bragg diffractors, reflecting EUV light at λ=13.5 nm via interlayer interference
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
The present invention provides a local clean microenvironment near optical surfaces of an extreme ultraviolet (EUV) optical assembly maintained in a vacuum process chamber and configured for EUV lithography, metrology, or inspection. The system includes one or more EUV optical assemblies including at least one optical element with an optical surface, a supply of cleaning gas stored remotely from the one or more optical assemblies and a gas delivery unit comprising: a plenum chamber, one or more gas delivery lines connecting the supply of gas to the plenum chamber, one or more delivery nozzles configured to direct cleaning gas from the plenum chamber to a portion of the EUV assembly, and one or more collection nozzles for removing gas from the EUV optical assembly and the vacuum process chamber.