AMC solutions prompt ESD fight

08/01/2000

Lisa Coleman

FRANKFURT, GERMANY—As design rules drop to 0.18 micron, finding a solution to airborne molecular contamination (AMC) is proving crucial to makers of 300-mm semiconductor wafers, says Stephan Ziegart, who is responsible for the design and construction of cleanrooms for Wacker Chemie GmbH (Burghausen, Germany).

At June's CleanRooms Europe 2000 held here, Ziegart highlighted possible solutions to AMC, however some of the measures for combating AMC offer new challenges—among the most serious is electrostatic discharge control.

Will manufacturers of the so-called "pizza wafers" now have to choose which contaminant they must attack? Possible measures against ESD include reducing the wafer's surface water film by decreasing air humidity.

"The solution to decrease the room relative humidity is rather a theoretical measure," says Ziegart. "If the room RH is decreased below 30 to 40 percent, ESD problems would. Personnel exposure to relative air humidity less than 30 percent is not recommended."

Other ways to combat AMC, according to Ziegart, include treating outside air using air washers and activated carbon filters; chemically treating recirculation air; reducing handling time; and reducing laminar airflow.

Currently, standardization efforts are underway by ISO/TC209/Working Group 8 to establish guidelines for AMC. The working group was formed in 1998 and its scope includes quantitatively classifying cleanrooms to contamination levels for AMC, specifying sampling strategies and describing methods of measurement for classification. A final working draft document is expected in 2001.