Methods and apparatus for substrate processing are described. In some embodiments a showerhead assembly includes a heated showerhead having a heater and a gas diffusion plate coupled to the heater, the gas diffusion plate having a plurality of channels extending through the gas diffusion plate; an ion filter spaced from the heated showerhead, the ion filter having a first side facing the heated showerhead and a second side opposite the first side, the ion filter having a plurality of channels extending through the ion filter; a heat transfer ring in contact between the heated showerhead and the ion filter, the heat transfer ring being thermally conductive and electrically insulative, the heat transfer ring comprised of a plurality of elements spaced from one another along an interface between the heated showerhead and the ion filter; and a remote plasma region defined between the heated showerhead and the ion filter.