Effects of size, humidity, and aging on particle removal from Si wafers

The effects of particle size, humidity, and aging time on particle removal from silicon wafers were investigated with a laser shock wave at a constant removal force. Particle adhesion force, shock wave cleaning force, and the removal moment ratio were calculated and related to particle removal efficiency (PRE). The presence of capillary forces and particle deformation significantly increased the adhesion force. In order to control the humidity and magnitude of deformation, humidity and aging time were varied during particle removal tests. PRE decreased rapidly for particle sizes below 1 μm as the humidity and contact area increase. The calculations of removal moment ratios agreed well with the experimental observations. Both humidity and process time should be controlled to avoid the aging of particles and to achieve high PRE for particles smaller than 1 μm.