Et tu, clean room filter? - filters used to keep rooms clean during the manufacture of computer chips may in themselves be a source of contamination - Materials Science - Brief Article

Science News, Oct 19, 1996

During a computer chip's manufacturing process, even minuscule amounts of dust or organic chemicals drifting through the air can spell ruin. That's why chips are assembled in clean rooms, where the air is filtered and everyone entering must, like surgeons, don protective caps, gowns, and booties. But now, accord- ing to a report in the September Journal of the Electrochemical Society, it seems that even the filters-whose job it is to keep the bad stuff out-can be a potential source of contamination.

Researchers at Eastman Kodak Co. in Rochester, N.Y., discovered that phosphorus was contaminating their chips somewhere along the 200-step manufac- turing process. They narrowed the problem down to a few stages in one clean room, then realized that the contamination had begun after the installation of some new, high-performance filters.

Sure enough, the polyurethane coating used to attach the paper filters to their metal frames gave off a phosphorus-containing substance. "Phosphorus shouldn't be in polyurethane," says John A. Lebens, a research scientist at Kodak and coauthor of the report. It turned out that the contaminant was in a flame retardant added to the coating. It doesn't take much phosphorus to wreak havoc, Lebens points out. It evaporates easily and settles on chips left in the open, altering their electrical properties.

It took the group 3 months to isolate the source of the contamination. The filters pull so much air through them, Lebens says, that "if it goes on for years, it can ruin your whole clean room." Luckily, only a few of the new fil- ters were in use and the filter manufacturer corrected the problem readily.

"We look at our filters very carefully now," Lebens says.