Provided is a flow rate control method, including: supplying fluid from a valve to a first sensor; measuring, by the first sensor, a first temperature of the fluid, and heating the fluid; measuring, by a second sensor, a second temperature of the heated fluid, and determining, by a controller, a first flow rate of the fluid based on comparison between the first temperature and the second temperature; supplying the fluid to a chamber and supplying an ignition voltage to the chamber through a radio frequency (RF) power source; measuring, by a third sensor, the ignition voltage; comparing, by the controller, the ignition voltage and a reference voltage to determine a second flow rate of the fluid; and controlling a supply of the fluid from the valve based on at least one of the first flow rate and or the second flow rate.