Readers have asked whether or not cleaning agents or classes of cleaning agents can be used for cleaning the cleanroom. For example, one person had been informed that all cleaning agents for use in cleanrooms have to be acidic. We are not aware of any such encompassing, universal proscriptions. Therefore, we decided to ask a few of the usual (and unusual) suspects. The responses did not point to bans on specific chemicals. Instead, there were trends and guidelines.
Non-viable contamination, AMC
In terms of airborne molecular contamination (AMC), Jürgen Lobert, Director of AMC Technology at Entegris Inc., Franklin, Mass., indicates that he is not aware of any semiconductor industry-wide standards for the use of chemicals in cleanrooms in general, or cleaning solutions in particular. Lobert says, “What is of concern is highly dependent on the process.”
Lobert, who is leading the current review of SEMI F21-110291, adds that, “The general approach these days is to keep everything as low as possible to prevent any potential process issues. Typical concentrations of AMC in semiconductor cleanrooms are on the order of 10 ppb or less; a high level would be in the tens of ppb.”
The SEMI standard categorizes AMC in terms of acids, bases, condensibles, and dopants. Lobert explains that “SEMI F21-1102 only describes the most important AMC classes, but does not cover all concerns, which often are OEM-, environment-, or process-specific.” Lobert adds that while the biggest concern is still with more condensable organics, recently some volatile organic AMC is getting more attention, even though they are not included in SEMI F21-1102. He concludes that widely used isopropyl alcohol and acetone do not have process impact; however, increasing process sensitivity may trigger more scrutiny of other cleaning agents.
Currently, chemical speciation of organic AMC is less of an issue than total concentrations. Lobert comments that, with the exception of siloxanes, there are rarely inquiries about the chemical nature of organic AMC. Given the potential for chemical reactivity with the surface and given the complexity of many janitorial cleaning agent formulations, it might seem logical that the next stage of process concern with AMC ought to include identification of specific constituents.
Life science specificity
Additional complexities arise when both viable and non-viable contamination must be considered. Greg Heiland, president and CEO of Valutek, Phoenix, and director of the Global Society for Contamination Control (GSFCC), explains that, where viable contamination is an issue, organisms can find ways to “outsmart” the cleaning agent, so disinfectants are typically rotated every 30 days. Perhaps in part because organisms are adaptable, the emphasis is on guidance documents. So, for example, ASTM E26142 includes considerations in selection of disinfectants for cleanrooms and recommendations for appropriate test methods rather than “musts” and “must nots.”
Kevina O’Donoghue, microbiologist at Micro Matters, Galway, Ireland, comments that while she is not aware of a requirement to use only a narrow range of cleaning agents, chlorine-based cleaning agents predominate “due to their high efficacy for cleaning everything.” O’Donoghue adds that her current cleaning programs designed for individual companies involve cleaning cleanrooms, choosing disinfectants, and putting in place an effective cleaning plan. This involves “choosing the correct disinfectant, rotation pattern, frequency of use, and evaluating the current environmental monitoring plan as it relates to the type of contamination present in your cleanroom. In other words, it is specific for you.”
O’Donoghue states, “There is lack of knowledge surrounding the use of and rotation of correct disinfectants. When asking people who work in cleanrooms why they use a certain disinfectant, the most common reply is ‘because the SOP says to’ or ‘another company uses them and says they are great’. There is a lack of awareness as to why we need to choose and rotate disinfectants correctly—not just to meet regulations.”
Practical considerations
Jeff Becker, president of Pegasus Cleanroom Services in San Diego, indicates that one major problem is to assure that the chemicals used to clean the cleanroom itself do not leave a residue that might interfere with the product and that the rinsing process and the quality of the rinse water is also of concern. Becker asserts that the choice of cleaning chemical may be based on company policy, preference, or experience. “If the company has an SOP,” Becker explains, “we use the specified chemical.”
On the other hand, Becker notes that startup companies may either underspecify or overspecify cleanroom cleaning. A company may have no immediate plans for cleaning, leaving Becker to select a “default” cleaning process. At the other extreme, an engineer at a startup company may have a background with a large pharmaceutical company. Becker explains that such an individual “may specify a complex cleaning protocol that is not necessary for the application, one that comes with a significant sticker shock.”
Moving forward
While we have not found overall, universal constraints on cleanroom chemicals, care in the selection and application of chemicals are needed for janitorial cleaning and disinfection. Many of the comments apply to direct cleaning of the product as well.
“Cleaning the cleanroom is difficult and a job that is often underappreciated,” concludes O’Donoghue. She adds that, too often, “companies select cleaning/disinfectant products based on a good sales pitch without a clear determination that the products will be effective in their cleanroom or if they will leave undesirable residues. Many do not realize how much work goes into cleaning a cleanroom effectively.”
Heiland cautions, “One elephant in the room is that people want to use cleaning agents that are as effective as possible. The processes are designed around cleaning efficiency, around product protection, not around operator protection.” Heiland calls for industry to “consider an encompassing standard for cleanroom cleaning products that include both efficacy of cleaning and a guide to operator safety.” One might add that recognition of environmental regulations would also be productive.
It’s not so much what you can use in a cleanroom overall, it is more what you need to use to minimize undesirable contamination in materials that are directly applied to the product and to the environment in which the product is manufactured. This being said, proving a negative is difficult, so if an all-encompassing standard has been overlooked, readers are invited to provide comments.
References
• SEMI F21-1102 – Classification of Airborne Molecular Contaminant Levels in Clean Environments.
• ASTM E2614, “Standard Guide for Evaluation of Cleanroom Disinfectants.”
Barbara Kanegsberg and Ed Kanegsberg (the Cleaning Lady and the Rocket Scientist) are independent consultants in critical and precision cleaning, surface preparation, and contamination control. They are the editors of The Handbook for Critical Cleaning, Second Ed., CRC Press. Contact: [email protected].
This article appeared in the April 2013 issue of Controlled Environments.
