Abstract: A processing chamber is adapted to perform a deposition process on a substrate. The chamber includes a pedestal adapted to hold a substrate during deposition and a gas mixing and distribution assembly mounted above the pedestal. The gas mixing and distribution assembly includes a face plate, a dispersion plate mounted above the face plate, and a mixing fixture mounted above the dispersion plate. The face plate is adapted to present an emissivity invariant configuration to the pedestal. The mixing fixture includes a mixing chamber to which a process gas is flowed and an outer chamber surrounding the mixing chamber. The processing chamber further includes an enclosure and a liner installed inside the enclosure and surrounding the pedestal. The liner defines a gap between the liner and the enclosure. The gap has a minimum width adjacent an exhaust port and a maximum width at a point that is diametrically opposite the exhaust port.