Bacteria as a Particle Source in Wafer Processing Equipment

Contamination control in integrated circuit wafer processing has become a major concern within the last two to three years. The surface particle counters and liquid particle counters have identified many particle sources within wafer processing equipment. One of these sources which is often overlooked is bacteria from the deionized water which is utilized in various etch, clean, rinser/dryers, scrubbers, and positive photoresist develop systems. Bacteria as live or dead microorganisms or as fragments of these microorganisms are a particle source and are a source of low level metals contamination. Bacteria in equipment is overlooked by many integrated circuit manufacturers and was not addressed by equipment manufacturers until recently. In many cases, integrated circuit manufacturers monitor only final rinse tanks or quick dumps for bacteria level and do not sample the bacteria level from all sources of equipment. By testing for bacteria level at every source of water that comes in contact with the waters, one finds many areas of stagnant water where the bacteria counts are too-numerous-to-count (TNTC). The causes for these high bacteria counts are dead legs (plumbing within equipment which has stagnant water flow), water velocities too low, inadequately sized plumbing, and materials used in the plumbing of the equipment. The solutions to these problems must be addressed by equipment users and manufacturers modifying existing equipment and designing new equipment with bacteria control as a primary concern.