Inductively Coupled Plasmas Generated Using Non-Sinusoidal Current Waveforms

Inductively coupled plasmas (ICP) are widely used for microelectronics fabrication. ICPs are usually generated using sinusoidal radiofrequency (RF) current. We study the role of RF frequency and current waveform on ICP plasma characteristics. This investigation is done using (a) a particle-in-cell (PIC) model of Ar plasma and (b) a Monte Carlo model to examine electron kinetics in plasmas of larger molecules (e.g., Cl₂, O₂, CF₄). The PIC simulations of the multi-turn ICP are first done for 5 – 30 MHz sinusoidal current. The plasma is produced slightly closer to the coil at higher frequency due to a smaller skin depth. A lower current is needed at higher frequency to produce plasma with similar density. The mean electron energy decreases with increasing plasma density and increases with RF frequency. This results in the production of more Ar^* than Ar⁺ at higher currents and lower frequency. Non-sinusoidal current waveforms have a mix of harmonics and can be useful to control the EEDF and plasma chemistry. This is demonstrated for sawtooth and pulsed DC waveforms in Ar using the PIC simulations. More complex chemistries are examined using a Monte Carlo model which computes the EEDF and rate of production of the different species.