Direct ion flux measurements at high-pressure-depletion conditions for microcrystalline silicon deposition

The contribution of ions to the growth of microcrystalline silicon thin films has been investigated in the well-known high-pressure-depletion (HPD) regime by coupling thin-film analysis with plasma studies. The ion flux, measured by means of a capacitive probe, has been studied in two regimes, i.e., the amorphous-to-microcrystalline transition regime and a low-to-high power regime; the latter regime had been investigated to evaluate the impact of the plasma power on the ion flux in collisional plasmas. The ion flux was found not to change considerably under the conditions where the deposited material undergoes a transition from the amorphous to the microcrystalline silicon phase; for solar-grade material, an ion-to-Si deposition flux of ~0.30 has been determined. As an upper-estimation of the ion energy, a mean ion energy of ~19 eV has been measured under low-pressure conditions