Gas delivery system for outputting fast square waves of process gas during semiconductor processing

A gas delivery apparatus to output a process gas to a semiconductor process as rapid square waves by increasing a time constant to a desire time constant, comprising:

• an enclosure attached to a base with a conduit channeling through the base to receive a supply of the process gas and output the process gas from the gas delivery apparatus to the semiconductor process;
• a wave generation component comprising a gas supply component and an on-off valve downstream from the gas supply component, coupled to receive the process gas in the conduit, the wave generation component during an off cycle when the on-off valve is closed to build pressure from the process gas in an accumulation volume, and during an on cycle when the on-off valve is open to release the process gas according to a time constant;
• and
• a flow restrictor installed in a throat of the on-off valve to output the rapid square waves to the conduit at a desired magnitude of flow, a size of the flow restrictor selected to have an impedance that is high enough to significantly raise the time constant during the on cycle such that massflow decay in each square wave pulse over the on cycle decreases to within a certain tolerance, wherein the time constant is at least in part a function of the flow restrictor impedance.