A continuous particle monitoring system was set up to. identify short-term particle bursts that reflect equipment operation and personnel activity within the photolithography bay of a cleanroom. The frequency and magnitude of the bursts vary with location and strongly depend on airflow, especially departures from vertical laminar flow introduced by equipment placement and/or human traffic. For example, the particle concentration above a stepper electronics cabinet was significantly reduced by moving the cabinet away from the cleanroom wall. Also, the particle concentration above the photoresist coater is very high during the operation of the wafer spinner; therefore, particles generated should be swept away by the airflows in order to minimize the particle transport to the wafer processing area.
Numerical simulation of the airflow around two selected pieces of processing equipment was performed to better explain particle transport from these sources. Zones of recirculation and particle trapping, as predicted by this modeling, were shown to exist near the equipment. The improvement in airflow distributions results in more complete and rapid removal of particles from the vicinity of the equipment.