Defect control and stability of DC bias in RF plasma-based substrate processing systems using molecular reactive purge gas

A substrate processing system comprises an upper electrode and a lower electrode arranged in a processing chamber. A gas delivery system selectively delivers at least one of precursor, one or more deposition carrier gases and a post deposition purge gas. An RF generating system deposits film on the substrate by generating RF plasma in the processing chamber between the upper electrode and the lower electrode by supplying an RF voltage to one of the upper electrode and the lower electrode while the precursor and the one or more deposition carrier gases are delivered by the gas delivery system. A bias generating circuit selectively supplies a DC bias voltage to one of the upper electrode and the lower electrode while the post deposition purge gas is delivered by the gas delivery system. The post deposition purge gas that is delivered by the gas delivery system includes a molecular reactant gas.