Patent ID: 8397739

Claim:
A method of calibrating a flow ratio controller for a tandem chamber having two process chambers, each process chamber having a gas diffuser comprising multiple gas zones disposed therein, each gas zone of each gas diffuser coupled to the same process gas supply, comprising: a) setting a first channel of a flow ratio controller coupled to the process gas supply to a 100 percent set point; b) setting all remaining channels of the flow ratio controller to a zero percent set point; c) closing all downstream isolation valves for the remaining channels of the flow ratio controller that are set at the zero percent set point; d) setting the flow of a mass flow controller equal to the flow of the 100 percent set point of the first channel; e) stabilizing the flow of a process gas through the flow ratio controller; f) calculating a span correction factor for the flow of the process gas through the first channel of the flow ratio controller; g) calculating a span correction factor for the flow of the process gas through the remaining channels of the flow ratio controller, comprising individually setting the flow ratio controller for each remaining channel to the 100 percent set point, and repeating elements (b)-(f) for each of the remaining channels; and h) determining the corrected set point for each channel of the flow ratio controller.