An apparatus is provided for obtaining very high quality films by chemical vapor deposition in situations where the deposition is mass transport limited. In accordance with the preferred embodiments, there is provided a vacuum housing which is actively cooled to a temperature below which deposition occurs, while at the same time the wafers are being heated to cause deposition at the wafer surfaces. Also provided are mixing chamber systems to ensure that reactant gases are well mixed and distributed evenly over each wafer surface. Mass transport control is further enhanced by provided an exhaust manifold which scavenges reactant gases from locations distributed throughout the system to achieve an even exhaust. Also provided is a method for depositing silicon-rich tungsten silicides using the above apparatus.