A method and apparatus for providing flow into a processing chamber are provided. In one embodiment, a vacuum processing chamber is provided that includes a chamber body having an interior volume, a substrate support disposed in the interior volume and a gas distribution assembly having an asymmetrical distribution of gas injection ports. In another embodiment, a method for vacuum processing a substrate is provided that includes disposing a substrate on a substrate support within in a processing chamber, flowing process gas into laterally into a space defined above a gas distribution plate positioned in the processing chamber over the substrate, and processing the substrate in the presence of the processing gas.