Patent ID: 7706925

Claim:
A pressure and flow ratio control system comprising: a plurality N of mass flow controllers MFC i (i=1, . . . , N) each configured to receive at an inlet an i-th one of a plurality N of fluids F i (i=1, . . . , N) and to control flow rate of the i-th fluid F i from the inlet through an outlet of the MFC i and directly into a processing chamber, without an intermediate manifold, the N mass flow controllers MFC i (i=1, . . . , N) including one master MFC and a plurality (N−1) of slave MFCs; wherein the master MFC is configured to receive flow ratio set points from a host controller, and to communicate the flow ratio set points to all the slave MFCs together with one or more command signals, so as to maintain ratios Qi/Q T (i=1, . . . , N) at the flow ratio set points, where Q i represents flow rate of the i-th fluid F i , and Q T represents a sum Q T =Q 1 +. . . +Q i +. . . Q N of flow rates of all N individual fluids F i (i=1, . . . , N); and wherein one of the mass flow controllers MFC i (i=1, . . . , N ) is a pressure control MFC configured to receive a pressure set point from the host controller and to maintain pressure in the chamber at the pressure set point by regulating flow to the processing chamber, and remaining ones of the mass flow controllers MFC i (i=1, . . . , N) are (N−1) flow control MFCs configured to control the flow rates Q i so as to maintain the flow ratios Q i /Q T at the flow ratio set points.