Abstract: A gas curtain for use with a semiconductor processing system to prevent unwanted gases from entering a processing chamber. The gas curtain includes both upward and downward flows of gas surrounding an isolation valve adjacent a delivery port into the processing chamber. In the valve open position, the downward flows extends between the valve and the delivery port, and the upward flow extends in an opposite direction behind the isolation valve. In the valve closed position, one of the flows extends through a slot in the isolation valve, while the other flow is directed in an opposite direction on the rear side of the isolation valve. In a method of using the gas curtain apparatus, a pick-up wand operating on a Bernoulli principal uses gases which are unwanted in the processing chamber, and just prior to loading wafers into the processing chamber, the gas flow in the Bernoulli wand is switched from a first gas to a second gas. Desirably, the second gas is hydrogen.