Flow control of process gas in semiconductor manufacturing

An apparatus for semiconductor manufacturing requiring the delivery of a process gas batchwise at a controlled flow rate during said manufacturing, said apparatus comprising, in combination, a source of pressurized process gas, a semiconductor manufacturing apparatus, and a flow control system operable in a flow mode for delivery of a batch of process gas from said source of pressurized process gas to said semiconductor manufacturing apparatus and, alternately, in a no-flow mode, said flow control system comprising:

• a flow line through which process gas from said source of pressurized process gas can be delivered,
• a pressure regulator in said flow line to establish a regulated process gas pressure in said line,
• an on/off valve in said line downstream of said pressure regulator to start and stop said flow mode during which said gas is delivered for a delivery period of time,
• a reference capacity in said flow line upstream of said pressure regulator for use in measuring the actual flow rate of gas being delivered by said flow control system,
• a pressure sensor to measure a pressure drop of said gas in said reference capacity during a measurement period of time commencing after the start of a delivery period of time,
• means in said line for interrupting the flow of process gas from said source of pressurized process gas to said reference capacity during delivery of said process gas by said flow control system, and
• a controller for determining from said measured pressure drop the rate of pressure drop in said reference capacity during said measurement period of time the actual flow rate of a batch of process gas being delivered and, in case said actual flow rate does not agree with a specified flow rate for said delivering, adjusting said controlled flow rate in the direction of said specified flow rate from said actual flow rate for a subsequent delivery period of time in which another batch of process gas is delivered.