Patent ID: 7314537

Claim:
A plasma processing system comprising: a processing tool having a process chamber; means coupled to the process chamber for providing in the process chamber at least two signals in a frequency range effective to couple energy to and from a plasma in the process chamber, depending on the parameters of the system, the signals including a first signal at a first frequency and a second signal at a second frequency selected to produce an inter-modulation product at a third frequency in said frequency range that is neither equal to nor a multiple of the first frequency or the second frequency; means for detecting the inter-modulation product from energy coupled from a plasma in the chamber; and means coupled to the means for detecting the inter-modulation product, said coupled means programmed for producing an output signal indicating the presence of a plasma in the chamber in response to the detection of the inter-modulation product and indicating the absence of a plasma from the chamber in response to an absence of the detection of the inter-modulation product.