Embodiments of the invention relate to apparatuses and methods for depositing materials on substrates during atomic layer deposition processes. In one embodiment, a chamber for processing substrates is provided which includes a chamber lid assembly containing an expanding channel at a central portion of the chamber lid assembly, wherein an upper portion of the expanding channel extends substantially parallel along a central axis of the expanding channel, and an expanding portion of the expanding channel tapers away from the central axis. The chamber lid assembly further contains a conduit coupled to a gas inlet, another conduit coupled to another gas inlet, and both gas inlets are positioned to provide a circular gas flow through the expanding channel. In one example, the inner surface within the upper portion of the expanding channel has a lower mean surface roughness than the inner surface within the expanding portion of the expanding channel.