Embodiments described herein provide a backside gas delivery assembly that prevents inert gas from forming parasitic plasma. The backside gas delivery assembly includes a first gas channel disposed in a stem of a substrate support assembly. The substrate support assembly includes a substrate support having a second gas channel extending from the first gas channel. The backside gas delivery assembly further includes a porous plug disposed within the first gas channel positioned at an interface of the stem and the substrate support, a gas source connected to the first gas channel configured to deliver an inert gas to a backside surface of a substrate disposed on an upper surface of the substrate support, and a gas tube in the first gas channel extending to the porous plug positioned at the interface of the stem and the substrate support.