Abstract: A gas distribution system for improving asymmetric etching and deposition control over a substrate diameter in a plasma reactor including a plasma reactor chamber further comprising a substrate holder for holding a substrate surface disposed in a lower portion of said plasma reactor; at least one gas distributor disposed within the plasma reactor chamber for distributing reactant gases said at least one gas distributor including a plurality of gas feed zones in communication with at least one gas source for selectively delivering a gas flow independently to at least one of the plurality of gas feed zones.