Plasma-assisted wafer de-chucking (power-lift) process induced charging damage

Charging damage from plasma-enhanced dielectric deposition has been well known for many years. The mechanism involved, however, is still not fully understood. A common practice in plasma processing of insulated films, both for dielectric deposition and etching, is to neutralize residual charges in the film with low-power plasma at the end while the wafer is being lifted for unloading. This is done to prevent unexpected movement of the wafer due to electrostatic force, which can lead to wafer crashing during unloading. It was reported that this final plasma-assisted wafer de-chucking (power-lift) step could cause significant damage (Cheung et al, 1997). The combination of charging damage during deposition and power-lift causes very severe damage to the gate-oxide. In most reported studies of charging damage during plasma enhanced dielectric deposition, whether or not the power-lift has been part of the process is not specified. Such uncertainty would complicate attempts to construct a model for the damage mechanism. The power-lift process is still widely used in both dielectric deposition and etching processes, but there have been no reports on power-lift induced charging damage to date. In many situations, it is still desirable to have a power-lift process. We therefore studied the power-lift process using damage as a response to find a low-damage power-lift condition.