Embodiments of the present invention generally relate to a clamshell and small volume chamber with a fixed substrate support. One embodiment of a processing chamber includes a fixed substrate support having a substrate receiving surface, a pumping ring disposed around a perimeter of the substrate receiving surface, and a gas distribution assembly disposed over the fixed substrate support. The pumping ring forms at least a portion of a pumping channel and has one or more apertures formed therethrough. The chamber may further include a gas-flow diffuser disposed radially inward of the apertures of the pumping ring. Another embodiment of a processing chamber includes a first assembly comprising a fixed substrate support and a second assembly comprising a gas distribution assembly. The first assembly includes a first assembly body that is shaped and sized so that at least a portion of the first assembly body is below the substrate receiving surface of the substrate support. A hinge assembly couples the first assembly and the second assembly. The first assembly and the second assembly can be selectively positioned between an open position and a closed position.