Transporting FOUPs as a driver for ESD-induced EMI

FOUPs are constructed from insulative plastics. As such, they take on charges of multiple kilovolts and carry large electric fields with them. Because of the large size of the FOUP, appreciable fields extend for a distance of >30 cm from the FOUP and can reach many objects withing the cleanroom. When the fields intersect an ungrounded or poorly grounded conductor, metal-to-metal discharges can occur. These discharges, in turn radiate nanosecond pulses (transient EMI) which can disrupt robotics. This paper details the measurement of such transients in an operating 300 mm fab. The results show that EMI is created by manual handling of FOUPs but that charged FOUPs moving in an overhead track are a much greater cause of EMI with the potential for robotic difficulties.