Test shows progress in war against SO2


MINNEAPOLIS, Minn.-Recent independent testing of filter technology developed by Donaldson Company Inc. ( offers optimism in the battle against sulfur-dioxide (SO2) contamination in semiconductor manufacturing.

In an air-quality experiment carried out by engineers at Interuniversity Microelectronics Center (IMEC; Leuven, Belgium;, a leading European nanoelectronics research center, Donaldson’s filters for airborne molecular contamination (shown in photo) were found to reduce sulfur-dioxide levels to below 10 ppt (parts per trillion) in next-generation semiconductor processes.

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The IMEC experiment was designed to validate a new monitoring tool and to characterize air quality both upstream and downstream of chemically-treated filters on a 193-nm lithography scanner. According to Roel Gronheid, PhD, of IMEC’s lithography department, “Experimental purge gas monitoring equipment, GP-IC from DIONEX Corp. (Sunnyvale, Calif.;, was tested on the in- and outlet ports of the air filtration cabinet of IMEC’s ArF ASML PAS5500/1100 scanner.”

Dr. Gronheid says that the tests were designed to monitor filtering performance for a variety of acid contaminants, such as sulfur dioxide, nitrous acid, and nitrogen dioxide.

According to Donaldson, the experiment’s results mark the first time that SO2 levels downstream of the filters have been demonstrated, on-line, to be below 10 ppt-a potentially significant result for semiconductor fabs and tool manufacturers who are facing more stringent SO2 specifications on next-generation tools.

“While it is true that we continue to supply IMEC with filters, and have worked with them in the past to identify the quantity and type of condensable organic levels in their cleanroom, I don’t think that either IMEC or Donaldson’s intention had been to test the filters per se,” says James Empson, Donaldson’s global marketing manager/semiconductors. “Obviously, we are pleased with the high level of SO2 removal efficiency and thought the information was of significant enough interest to industry to publicize [it].”

Empson notes that “similar technology has been implemented in all of our current line of AMC cabinets, point-of-use filters, and passive adsorptive filters.” In addition, he says, Donaldson is developing a line of low-pressure drop filters that are designed to enable fabs “to address air quality throughout their process, with a high degree of confidence.” III