Abstract

A gas distribution system for processing a semiconductor substrate includes a plurality of gas supplies, a mixing manifold wherein gas from the plurality of gas supplies is mixed together, a plurality of gas supply lines delivering the mixed gas to different zones in the chamber, and a control valve. The gas supply lines include a first gas supply line delivering the mixed gas to a first zone in the chamber and a second gas supply line delivering the mixed gas to a second zone in the chamber. The control valve controls a rate of flow of the mixed gas in the first and/or second gas supply line such that a desired ratio of flow rates of the mixed gas is achieved in the first and second gas supply lines. In a method of using the apparatus, a semiconductor substrate is supplied to the reaction chamber and the substrate is processed by supplying the mixed gas to the first and second zones, the control valve being adjusted such that a rate of flow of the mixed gas in the first and/or second gas supply line provides a desired ratio of flow rates of the mixed gas in the first and second zones.