Systems and methods for reducing backside deposition and mitigating thickness changes at substrate edges

A method for depositing film on a substrate, comprising:

• arranging a substrate on a substrate support in a reaction volume of a processing chamber;
• selectively introducing process gases into the reaction volume of the processing chamber and generating RF plasma to deposit film on the substrate;
• clamping the substrate to the substrate support during deposition of the film;
• and
• supplying, as a purge gas, a reactant gas to a backside edge of the substrate to purge the backside edge of the substrate during the deposition of the film and during the generating of the RF plasma in the reaction volume,
• wherein, supplying the purge gas includes
• flowing the purge gas at a rate greater than or equal to 150 sccm to purge the backside edge during the generation of the RF plasma,
• providing molecular oxygen as the purge gas, and
• providing the molecular oxygen as the purge gas to (i) inhibit at least one of plasma light-up and hollow cathode discharge signatures proximate the backside edge during the generation of the RF plasma in the reaction volume and (ii) inhibit parasitic power loss associated with the purge gas.