Patent ID: 7632690

Claim:
A process for controlling etching on a semiconductor substrate wherein the etching is affected by the concentration of an etchant gas, and wherein the etchant gas is input to an etch chamber via a mass flow controller, the process comprising: determining a desired etchant gas concentration; supplying an inert gas to the etch chamber; producing a first signal representative of an actual etchant gas concentration; producing a second signal representative of an inert gas concentration; relating the first and the second signals to produce a normalized etchant gas concentration signal; employing a comparator having a first input terminal receiving the normalized etchant gas concentration signal and a second input terminal receiving a reference signal representing the desired etchant gas concentration, the comparator for outputting an error signal for controlling the mass flow controller, said error signal representing a difference between said reference signal and said normalized etchant gas concentration signal; and controlling the mass flow controller in response to the employing step.