The embodiments of the invention describe a process chamber, such as an ALD chamber, that has gas delivery conduits with gradually increasing diameters to reduce Joule-Thompson effect during gas delivery, a ring-shaped gas liner leveled with the substrate support to sustain gas temperature and to reduce gas flow to the substrate support backside, and a gas reservoir to allow controlled delivery of process gas. The gas conduits with gradually increasing diameters, the ring-shaped gas liner, and the gas reservoir help keep the gas temperature stable and reduce the creation of particles.