The study of capacitively-coupled hydrogen plasma at very high frequency

In the high rate deposition of device grade microcrystalline silicon films and their solar cells, plasma enhanced chemical vapor deposition excited using very high frequency (VHF) has become a mainstream method. Although, great breakthroughs in the experiment are achieved, the depositional mechanism is still a research hot spot and difficulty point. In this paper, the capacitively-coupled hydrogen plasma discharge at VHF is simulated. A two-dimensional, time-dependent axial symmetry model is adopted at a frequency of 75 MHz, and the influences of pressure and plasma power on hydrogen plasma characteristic are simulated. At the same time, the hydrogen plasma is monitored on-line using the optical emission spectrometry in experiment. The results show that the value of the electronic concentration ne takes a maximum in the middle of the plasma bulk, while the electron temperature Te and the number densities of Hα and Hβ each have a maximal value at the place near the sheath and plasma bulk; the potential decreases with pressure increasing from 1 Torr to 5 Torr, the electron concentration in the plasma bulk first increases with the increase of pressure, then decreases with the further increase of pressure, but the electron temperature first decreases and then keeps stable in plasma bulk; the electron concentrations, Hα and Hβ increase linely with power increasing from 30 W to 70 W, but the electron temperature keeps stable. The experimental results and simulation results are in good agreement.