CO2 Snow Cleaning Filter for EUV Lithography
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Solution Overview
Problem
Existing surface cleaning methods using liquid CO₂ fail to effectively filter out particles smaller than 0.1 µm, leading to surface contamination during the cleaning process, which is critical for maintaining optical system performance, especially in EUV lithography.
Innovation Solution
Implementing a particle filter with a retention rate of at least 0.1 µm, preferably 0.05 µm, made of materials like PTFE, PFA, or PET, and designed to withstand high pressures and flow rates, to ensure particle-free liquid CO₂ supply, followed by mixing with a gas to form a cleaning stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional particle filters are used to filter liquid CO2, then large particles can be removed, but particles smaller than 0.1 µm remain and cause surface contamination
Solution Approach 1:
The patent changes the filtration parameter from conventional filter ratings to a fine pore structure with retention rate of at least 0.1 µm, preferably at least 0.05 µm. This parameter change enables the filter to capture sub-micron particles that would otherwise contaminate optical surfaces during cleaning.
Solution Approach 2:
The patent employs a porous filter medium with specifically controlled pore sizes to achieve the required retention rate. The porous structure allows liquid CO2 to pass through while trapping particles down to 0.1 µm or smaller, depending on the filter's rated retention capability.
2Object-affected harmful factors
If a particle filter with retention rate of 0.1 µm or higher is implemented, then surface contamination is prevented, but the filter must withstand high pressures and flow rates which increases device complexity
Solution Approach 1:
The filter is designed and pre-configured to withstand the required operating conditions of high pressure and flow rate before actual use. The housing and filter medium are selected and assembled to meet the mechanical and operational requirements, eliminating the need for complex adaptive mechanisms during operation.
Solution Approach 2:
The filter assembly combines a porous filter medium with a robust housing structure made of materials suitable for high-pressure operation. This composite construction achieves both the fine filtration capability and the mechanical strength required without requiring overly complex individual components.
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
Prevents surface contamination by ensuring that particles smaller than 0.1 µm are filtered out, maintaining the cleanliness and performance of optical elements, particularly in EUV lithography systems.
Implementation Method 1
filtering particles contained in the liquid gas with a particle filter
Implementation Method 2
generating a solid in the form of CO2 snow from the liquid gas, preferably by expanding the liquid gas
Implementation Method 3
expelling the solid onto the surface to be cleaned
Data Source
Figure 1
Figure 2~4
AI summary
The invention relates to a method for cleaning a surface, more particularly a surface of an optical element, comprising: providing a liquefied gas (31) in the form of liquefied CO2; producing a solid in the form of CO2 snow from the liquefied gas (31), preferably by expanding the liquefied gas (31); and discharging the solid onto the surface to be cleaned. The method also comprises filtering particles contained in the liquefied gas (31) by means of a particulate filter (33) having a retention rate of at least 0.1 µm, preferably of at least 0.05 µm. The invention also relates to a cleaning device for cleaning surfaces, comprising: a providing apparatus (30) for providing a liquefied gas (31) in the form of liquefied CO2, a producing apparatus for producing a solid in the form of CO2 snow, preferably by expanding the liquefied gas (31), and a discharging apparatus for discharging the solid onto the surface to be cleaned. The providing apparatus (30) has at least one particulate filter (33) for removing particles contained in the liquefied gas (31), the particulate filter (33) having a retention rate of at least 0.1 µm, preferably of at least 0.05 µm. The invention also relates to an optical assembly having at least one cleaning device of this type.