Measuring the body voltage on wearers of category 3 bunnysuits

The electric field sensitivity of modern photolithographic reticles [1,2] and of magnetoresistive heads [1] is extreme. Many modern semiconductor components have CDM damage thresholds below 100 V and place similar demands in back end fabs and in electronics assembly [4]. Often this requires use of Category 3 [5] cleanroom garments designed to limit body voltage to 100 V [2]. A Charge Plate Monitor (CPM) is specified to measure body voltage [2]. This paper investigates the measurement accuracy. It is shown that the capacitance of measurement system causes the CPM to underestimate the walking voltage.