Process-induced oscillator frequency pulling and phase noise within plasma systems

Passive radio spectroscopy is employed to examine plasma process instabilities generated by the interaction between the power source oscillator and the plasma load. A fixed frequency of 13.56 MHz and a 170–180 kHz Flyback transformer are considered. The carrier frequencies are interrogated using a resolution bandwidth that constitutes ∼1/7000–1/580 of the target oscillator frequencies with a sweep time of less than 0.06 s across the phase noise disturbance. Within these spectrum analyzer measurement parameters, oscillator phase noise (1/fn=1–3, discrete spurs and raised noise floor) is shown to be linked to plasma load mismatch and periodic instabilities. In the case of the Flyback circuit, it is found that the oscillator frequency pulling and modulation are linked to the plasma reactance. These results indicate that oscillator phase noise can be used as a non-invasive plasma process metrology tool.