Methods, systems, and apparatus for mass flow verification based on choked flow

An electronic device manufacturing system, comprising:

• a mass flow controller;
• a mass flow verification system having an inlet and an outlet, the inlet coupled to the mass flow controller, the mass flow verification system comprising:
• a plurality of isolation valves coupled downstream of the inlet;
• and
• a plurality of differently-sized flow restrictors coupled in parallel and downstream of the inlet, each one of the plurality of differently-sized flow restrictors coupled in series with the inlet, a respective one of the plurality of isolation valves, and the outlet;
• a controller coupled to the plurality of isolation valves and configured to receive a pressure measurement and a temperature measurement upstream of the plurality of differently-sized flow restrictors under a choked flow condition through only one of the plurality of isolation valves, the controller also configured to determine a mass flow rate in response to receiving the pressure measurement and the temperature measurement;
• and
• a process chamber coupled to a flow path coupled to the mass flow controller and configured to receive one or more process chemistries via the mass flow controller.

A method of verifying a mass flow rate, the method comprising:

• causing a gas to flow through only one of a plurality of differently-sized flow restrictors during a choked flow condition;
• measuring a pressure upstream of the one of the plurality of differently-sized flow restrictors to obtain a measured pressure value during the choked flow condition;
• measuring a temperature upstream of the one of the plurality of differently-sized flow restrictors to obtain a measured temperature value during the choked flow condition;
• and
• determining a mass flow rate by applying a predetermined flow restrictor coefficient, a predetermined gas correction factor, and a predetermined temperature value to the measured pressure value and the measured temperature value.