Patent ID: 7628860
Filing Date: 2009-12-08
Classification: C23C,Y10S

Abstract:
1. A system for delivering a desired mass of gas, comprising: a chamber; a first valve controlling gas flow into the chamber; a second valve controlling gas flow out of the chamber; a pressure transducer providing measurements of pressure within the chamber; a controller connected to valves and the pressure transducer, wherein the controller is configured and arranged to: (i) receive a desired mass flow setpoint from an input device; (ii) close the second valve; (iii) open the first valve; (iv) receive chamber pressure measurements from the pressure transducer; (v) close the first valve when pressure within the chamber reaches a predetermined level; (vi) wait a predetermined waiting period to allow the gas inside the chamber to approach a state of equilibrium; (vii) open the second valve at time=t (viii) calculate a value of the total mass delivered when the second valve is open and as a function of temperature and pressure within the chamber; and (ix) close the second valve at time=t* when the calculated value of total mass delivered equals the desired mass flow setpoint, wherein t* is from about 100 milliseconds to about 500 milliseconds wherein the mass delivered Δm at time t*, is determined by the controller as: wherein m(t 0 ) is the mass of the gas in the delivery chamber at time =t 0 when the gas within the delivery chamber is at a state of equilibrium, m(t*) is the mass of the gas in the delivery chamber at time=t*, V is the volume of the delivery chamber, R is equal to the ideal gas constant (J/Kg−K), P(t 0 ) is the pressure in the delivery chamber at time=to, P(t*) is the pressure in the deliver chamber at time=t*, T(t 0 ) is the temperature in the delivery chamber at time=to, T(t*) is the temperature in the delivery chamber at time=t*.