Impedance match timing for pulsed RF control: Global model and validation experiments

Inductively coupled plasmas (ICPs) driven by pulsed RF power are used by the semiconductor industry to achieve the process demands for fabricating devices at the nanoscale. Existing global models offer valuable insight into the transient behavior of these plasmas but do not account for the external circuitry needed to deliver RF power from the generator to the plasma; this external circuitry not only distorts the plasma transient compared to idealized step-function power delivery, it also presents a low-barrier pathway for fine-tuning these transients to optimize power delivery within the pulse transient and enable control over the rate of increase of electron density ne and electron temperature Te in the early ON-cycle. This work presents a global plasma model with a coupled equivalent circuit model to elucidate the synergistic effects of a fixed impedance matching network and the time-varying impedance of a plasma load on the plasma transient response during the pulse cycle. The tuning of the impedance matching circuit to provide an ideal match condition at different points in time in the pulsed RF cycle is shown to provide a mechanism for controlling the rate of electron production at the start of the pulse. The delivered power and the centerline ne data were experimentally benchmarked against the modeling results in a cylindrical ICP reactor. The results were obtained for 99.999% argon at pressures between 20 and 50 mTorr. The measured densities range from 109 to 1011 cm−3 and show good agreement with the modeled predictions.