Cleaning Ultra High Vacuum Parts for Semiconductor Manufacturing and Similar Critical Cleaning Applications
Cleaning of ultra high vacuum parts is a critical step in ensuring a part functions properly and lasts as long as possible in an ultra high vacuum system. There are many factors to consider when cleaning an ultra high vacuum part, from the type of contaminant to the cleaning method itself. In this blog post, we will discuss some of the most common contaminants found in ultra high vacuum environments and how to best clean them.
What is an ultra high vacuum system?
Numerous industries require hardware operation at high levels of vacuum including applications in space satellites, semiconductor manufacturing, medical devices, and laboratory research.
Common processes include:
- Vacuum coating and deposition like Physical Vapor Deposition (PVD) or Ion Beam Sputtering (IBS)
- Particle accelerators
- Analytical processes such as mass spectroscopy
- Microwave vacuum electron communication devices
The level of required vacuum depends on the application and is commonly defined as:
- Extreme High Vacuum (XHV) less than 10-12 mbar
- Ultra High Vacuum (UHV) between 10-7 and 10-12 mbar
- High Vacuum (HV) between 10-7 and 10-3 mbar
As you can see, these are very extreme pressures where the smallest misstep could cause the loss of vacuum and a subsequent failure of the UHV chamber.
Why cleaning ultra high vacuum parts is important?
To permit operation under these conditions, components exposed to vacuum such as vessels, tubing, instrumentation, and structural elements must satisfy specific demands for outgassing. Outgassing is the release of contaminant materials adsorbed onto the part surface. This occurs when exposed to a sufficient level of vacuum. Too much outgassing of contaminants inhibits achieving the desired level of vacuum and vacuum retention.
Image Source: Product Finishing Magazine
Cleaning requirements and specifications
Metal parts that will be exposed to high and ultra high vacuum service conditions must fulfill specific requirements related to the cleaning process in order to ensure good performance in the eventual use of the part.
Cleaning of parts for UHV applications must:
- Effectively remove all the oils, greases, and other hydrocarbons that are commonly used during manufacture and assembly processes.
- Eliminate all the particulate matter larger than 0.005 inches (0.13 mm) in diameter that may be present on the part surface.
- Reduce the outgassing of cleaning solvent residues to an acceptable level.
- Be safe on the part material.
Outgassing rate measurements include both standardized ASTM E-1559 and proprietary methods specified by manufacturers of such hardware, who may also specify outgassing performance standards. The National Ignition Facility (NIF) also references specifications for both Gross Cleaning MEL99-009-OK and Precision Cleaning MEL00-016-OE which are important to the overall cleaning requirements.
What contaminants are of concern?
Contaminants in outgassing can include any residual material on part surfaces such as machining coolants used in part fabrication, residue of improperly specified cleaning detergents, and other contaminants.
Common examples of contaminants include:
- Particulate such as metal fines
- Oils and grease
- Remnants from not using deionized water
- Tape residue
How to clean parts used in an ultra high vacuum environment
The process for cleaning ultra high vacuum parts must minimize the residual potential sources of outgassing, as well as other contaminants and particulates that have hazards besides outgassing.
For this reason, the performance requirements of the cleaning detergent or solvent in the ultra high vacuum cleaning procedures are twofold; it must ensure not only sufficient removal of contaminants but also permit very thorough rinsing of the cleaning media itself from the part surface after the soil removal process (for example, a sufficiently free-rinsing aqueous detergent in a process with adequate rinsing capacity and control).
Ultra high vacuum cleaning equipment and processes resemble other precision cleaning applications. These can include aqueous processes like immersion with ultrasonics, spray wash, and rotating basket systems with various modalities of mechanical agitation. The aqueous process for ultra high vacuum parts typically includes a very thorough rinse process with multiple stages and tight final rinse water control requirements. Control of the drying step may need to be much tighter as well (i.e., drying with nitrogen, filtered to a specified standard, etc.)
Proven and cited parts cleaning chemistries
Many Brulin products have been evaluated to the aforementioned specifications and are known to sufficiently clean components to ensure parts function well during ultra high vacuum operation. AquaVantage 815 GD and 1990 GD have been well documented and cited for such use from a variety of sources.
Third-party testing and literature citations of Brulin chemistries:
- Meyer Tool
- Lawrence Livermore National Laboratories
- US Particle Accelerator School - multiple references including Lawrence Livermore and academic research institutions such as Cornell
- Multiple academic references such as Secondary Electron Yield Measurements on Materials of Interest to Vacuum Electron Communication Devices from the University of New Mexico
Several other chemistries such as AquaVantage 815 GD-NF and 3843 GD are also known to function well based on customer insight and third-party testing.
Additionally, there are several known or reported supplier approvals and recommendations for use of Brulin products (mostly 815 GD or 815 GD-NF) for cleaning ultra high vacuum parts. These include:
- Semiconductor equipment makers including those for manufacturers of specialized light sources used in lithography for semiconductor applications, thin-film processing including atomic layer deposition, and equipment for ion beam sputtering and laser thermal annealing equipment
- Contract cleaning service suppliers specializing in outsourced Ultra-High Vacuum (UHV) & Extreme High Vacuum (XHV) parts cleaning solutions
- In house cleaning by ultra high vacuum part suppliers following precision machining/ fabrication
We also have a Case Study from a vacuum vessel manufacturing customer for whom our 815GD has been tested and shown to give excellent results in preparation for an outgassing test and eventual vacuum service.
When cleaning UHV components, it is important to use a method that will minimize the number of residual contaminants. AquaVantage 815 GD and 1990 GD are two cleaning detergents that have been proven to be effective in cleaning ultra high vacuum parts. These detergents are effective in removing particulates, oils, and coolants from ultra high vacuum parts. In addition, they are also effective in the thorough rinsing of the cleaning media itself from the part surfaces after the soil removal process.
Q: What is the best detergent for cleaning ultra high vacuum parts?
A: Brulin AquaVantage cleaning detergents are some of the best cleaning agents for ultra high vacuum parts. These detergents are effective in removing dust, oil, and grease from ultra high vacuum parts. In addition, they are also effective in removing the cleaning media itself from the part surface after the soil removal process.
Q: How do I remove soils from my ultra high vacuum part?
A: There are many methods that can be used to remove contaminants from an ultra high vacuum part. Some common methods include ultrasonic cleaning, spray wash, and rotating basket systems with various modalities of mechanical agitation. It is important to select the cleaning method that is best suited for the type of contaminant that needs to be removed and the part complexity.
Q: What are some common contaminants found on ultra high vacuum parts?
A: Some common contaminants found on ultra high vacuum parts include particulate, oil, and grease. These contaminants can cause problems with the function of the part if they are not removed.
Q: How do I know if my cleaning detergent is effective in cleaning ultra high vacuum parts?
A: There are many ways to test the effectiveness of a cleaning detergent. One way is to use an outgassing test. This test measures the amount of gas that is emitted from a cleaned part.