A semiconductor wafer processing apparatus is provided with a susceptor for supporting a wafer for CVD of films such as blanket or selective deposition of tungsten or titanium nitride, and degassing and annealing processes. Preferably, a downwardly facing showerhead directs a gas mixture from a cooled mixing chamber onto an upwardly facing wafer on the susceptor. Smooth interior reactor surfaces include baffles and a susceptor lip and wall shaped to minimize turbulence. Inert gases flow to minimize turbulence by filling gaps in susceptor structure, prevent contamination of moving parts, conduct heat between the susceptor and the wafer, and vacuum clamp the wafer to the susceptor. A susceptor lip surrounds the wafer and is removable for cleaning, to accommodate different size wafers, and allows change of lip materials to for different processes, such as, one which will resist deposits during selective CVD, or one which scavenges unspent gases in blanket CVD. The lip smooths gas flow, reduces thermal gradients at the wafer edge. The susceptor design reduces heat flow from the susceptor to other reactor parts by conduction or radiation.