Embodiments of the present invention generally relate to chambers and methods of processing substrates therein. The chambers generally include separate process gas and purge gas regions. The process gas region and purge gas region each have a respective gas inlet and gas outlet. The methods generally include positioning a substrate on a substrate support within the chamber. The plane of the substrate support defines the boundary between a process gas region and purge gas region. Purge gas is introduced into the purge gas region through at least one purge gas inlet, and removed from the purge gas region using at least one purge gas outlet. The process gas is introduced into the process gas region through at least one process gas inlet, and removed from the process gas region through at least one process gas outlet. The process gas is thermally decomposed to deposit a material on the substrate.