A gas supply delivery arrangement for supplying process gas to a chamber of a plasma processing system wherein a semiconductor substrate is processed with gases introduced through at least first, second, and third gas injection zones, comprising: a plurality of process gas supply inlets and a plurality of tuning gas inlets; a mixing manifold comprising a plurality of gas supply sticks each of which is adapted to provide fluid communication with a respective process gas supply; a plurality of tuning gas sticks each of which is adapted to provide fluid communication with a respective tuning gas supply; a first gas outlet (C1, 40) adapted to deliver gas to the first gas injection zone, a second gas outlet (C2, 70) adapted to deliver gas to the second gas injection zone, and a third gas outlet (E1, 44) adapted to deliver gas to the third gas injection zone; a gas splitter in fluid communication with the mixing manifold, the gas splitter including: a first valve arrangement (730a, 730b) which splits mixed gas exiting the mixing manifold into: a first mixed gas and a second mixed gas; and a controller configured to operate valves of the first valve arrangement (730a, 730b) such that the first mixed gas is delivered only to the first gas outlet (C1, 40) and the second mixed gas is delivered only to the second (C2, 70) and/or third (E1, 44) gas outlets; and a second valve arrangement which selectively delivers tuning gas from the tuning gas sticks to the first (C1, 40), second (C2, 70) and/or third gas outlets (E1, 44). a plurality of process gas supply inlets and a plurality of tuning gas inlets; a mixing manifold comprising a plurality of gas supply sticks each of which is adapted to provide fluid communication with a respective process gas supply; a plurality of tuning gas sticks each of which is adapted to provide fluid communication with a respective tuning gas supply; a first gas outlet (C1, 40) adapted to deliver gas to the first gas injection zone, a second gas outlet (C2, 70) adapted to deliver gas to the second gas injection zone, and a third gas outlet (E1, 44) adapted to deliver gas to the third gas injection zone; a gas splitter in fluid communication with the mixing manifold, the gas splitter including: a first valve arrangement (730a, 730b) which splits mixed gas exiting the mixing manifold into: a first mixed gas and a second mixed gas; and a controller configured to operate valves of the first valve arrangement (730a, 730b) such that the first mixed gas is delivered only to the first gas outlet (C1, 40) and the second mixed gas is delivered only to the second (C2, 70) and/or third (E1, 44) gas outlets; and a second valve arrangement which selectively delivers tuning gas from the tuning gas sticks to the first (C1, 40), second (C2, 70) and/or third gas outlets (E1, 44). a first valve arrangement (730a, 730b) which splits mixed gas exiting the mixing manifold into: a first mixed gas and a second mixed gas; and a controller configured to operate valves of the first valve arrangement (730a, 730b) such that the first mixed gas is delivered only to the first gas outlet (C1, 40) and the second mixed gas is delivered only to the second (C2, 70) and/or third (E1, 44) gas outlets; and a first mixed gas and a second mixed gas; and a controller configured to operate valves of the first valve arrangement (730a, 730b) such that the first mixed gas is delivered only to the first gas outlet (C1, 40) and the second mixed gas is delivered only to the second (C2, 70) and/or third (E1, 44) gas outlets; and a second valve arrangement which selectively delivers tuning gas from the tuning gas sticks to the first (C1, 40), second (C2, 70) and/or third gas outlets (E1, 44).