  Radiofrequency capacitively coupled plasma is studied theoretically using a
Particle-in-Cell code. For He discharge, the time-averaged sheaths are in the
range of few centimeters. The sheath potential, ion, and electron energy and
angular distributions, discharge current, and dissipated power depend on the
driven potentials and frequencies. Increasing the amplitude of the high radio
frequencies increases the bulk density and the sheath potential and,
consequently, increases the plasma processing rate. Increasing the intermediate
radio frequency amplitude allows a wider sheath with a broad ion energy
distribution and a narrower ion angular distribution. Changing the amplitude
and the phase shift between driven frequencies provide different energies and
angular distribution allowing performing various processes. The interplay
between the sheath and bulk dynamics in the intermediate radiofrequency regime
and the high-frequency regime may excite harmonics in the discharge current.
