Hardware to prevent bottom purge incursion in application volume and process gas diffusion below heater

A method of processing a semiconductor substrate, comprising flowing a precursor into a semiconductor processing chamber via a showerhead that is disposed above a substrate support on which the semiconductor substrate is positioned;

• simultaneously flowing a purge gas through a purge lumen defined by an exterior surface of the substrate support and a liner that is spaced apart from the substrate support;
• an inner surface of the liner comprises a protrusion that extends inward toward the exterior surface of the substrate support;
• a lateral distance between the exterior surface of the substrate support and the protrusion is between about 60 mils and 100 mils;
• and diverting the purge gas laterally outward using an edge ring that is positioned atop a peripheral edge of the substrate support and that extends laterally outward of a top end of the purge lumen such that the purge gas and the precursor diffuse with one another at a diffusion position that is radially outward of a bevel of the semiconductor substrate.