Embodiments as described here provide an apparatus and a method for performing an atomic layer deposition process. In one embodiment, a deposition chamber assembly contains a substrate support having a substrate receiving surface, and a chamber lid containing a tapered passageway extending from a central portion of the chamber lid and a bottom surface extending from the passageway to a peripheral portion of the chamber lid, the bottom surface shaped and sized to substantially cover the substrate receiving surface. The system also includes one or more valves coupled to the gradually expanding channel, and one or more gas sources coupled to each valve. In one example, the gas source is an ampoule assembly which is attached to the deposition chamber by at least one disconnect fitting and contains an inlet tube directed away from the gas outlet.