Gas distribution apparatus for semiconductor processing

A method of processing a substrate in a reaction chamber wherein a gas distribution system 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, the gas supply lines including 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, at least one control valve controlling 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, at least one flow measurement device measuring flow rate of mixed gas in the first and/or second gas supply line, and a controller operating the at least one control valve in response to the flow rate measured by the at least one flow measurement device, the process comprising:

• supplying a semiconductor substrate to the reaction chamber;
• measuring flow rate of mixed gas in the first and/or second gas supply line with at least one flow measurement device;
• and
• processing the substrate by supplying the mixed gas to the first and second zones, the at least one control valve being adjusted by the controller in response to the flow rate measured by the at least one flow measurement device.