Experts make case for AMC standards

Experts make case for AMC standards

Hank Hogan

Just like the weather, everyone may be worried about airborne molecular contaminants (AMCs), but no one is sure what to do about them. Different groups are either working on or have developed industry-specific standards for semiconductors, disk drives, biotechnology, and aerospace.

The concern about AMC and these widespread efforts led the ISO/TC 209 committee — charged with overall cleanroom standards worldwide — to hold a meeting concurrent with the Institute of Environmental Sciences and Technology (IEST) gathering in Phoenix in late April on setting AMC standards. The committee hosted a panel discussion followed by a question and answer session. The consensus was that worldwide and industry-spanning standardization would take some time to develop and involve some basic steps first.

“We talked about what might be standardized and, number one, you`d probably start with terminology,” reports Mark Camenzind, a senior research chemist at Balazs Analytical Laboratory of Sunnyvale, CA. Camenzind presented a paper on a role for ISO/TC 209 standards for AMC in cleanrooms.

In his talk Camenzind pointed out that cleanrooms are clean for particles only. They`re actually dirty for molecular contaminants. Filters that easily handle 0.1-micron particles are not adequate for molecules that are smaller than 50 angstroms (0.005 microns). At times filters have even been known to contribute to the AMC problem. Airborne etchants can attack filters, release dopants into the air, and cause anywhere from 15 to 100 percent semiconductor yield losses.

Besides Camenzind, others on the panel were David Ensor of the North Carolina-based Research Triangle Institute; Eugene Borson, a consultant to the aerospace industry; and Bill Bowers of Femtometrics Inc. of Irvine, CA. Ensor presented a broad overview, while Borson focused on the aerospace industry and Bowers zoomed in on surface acoustic wave technology with real-time analysis capabilities. Despite the different backgrounds and agendas, the group as a whole was clear on the need for AMC standards.

“We were a fairly unified choir,” re calls Ensor.

He also says that the meeting room was packed with 70 or so attendees for the panel discussion as well as the question and answer session. Numerous examples of problems with AMC emerged during the audience give-and-take, ranging from well-documented semiconductor yield losses due to dopant outgassing to less widely known issues involving the farming of mushrooms in clean environments. International interest was also evident with a contingent present from Japan.

“It was a very positive and lively discussion,” says Ensor. “Certainly it was very persuasive, because the 209 committee went forward to set up a new working group.”

The working group, dubbed working group 8, is charged with developing worldwide, non-industry specific standards. As might be imagined, this is a difficult assignment. Harmonizing differing standards across divergent industries is a challenge. Even getting numbers for meaningful comparisons is not easy because, as Camenzind points out, each analytical lab uses its own techniques and methods.

Hammering out agreements on analysis will be hard enough. Harder still will be coming up with standards that cover AMC removal by filters. Equally difficult would be the creation of guides to standard practices covering sampling times or sites. Given the diversity of industries involved, Camenzind believes that some of the details may come out of such industry groups as Semiconductor Equipment and Materials International (SEMI) or the International Disk Drive Equipment and Materials Association (IDEMA). Many of these groups either already have or are working on their own standards.

The ISO/TC 209 working group has already met once. According to Anne Marie Dixon of Cleanroom Management Associates Inc. (Carson City, NV), who sits on the ISO/TC 209 committee, there`s no output yet from the group. Minutes for the kick-off meeting were being distributed at press time, and after that is done, it will take some time to cobble together a United States delegation to the world organization.

Hank Hogan is a freelance writer based in Austin, TX. He has written for New Scientist, High Technology Careers, Electronic Components, and Multichannel News International. He was previously a semiconductor process engineer and holds a process technology patent.


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