Growth mechanisms study of microcrystalline silicon deposited by SiH_4/H_2 plasma using tailored voltage waveforms

摘要

The use of Tailored Voltage Waveforms is a technique wherein one uses non-sinusoidal waveforms with a period equivalent to RF frequencies to excite a plasma. It has been shown to be an effective technique to decouple maximum Ion Bombardment Energy (IBE) from the ion flux at the surface of the electrodes. In this paper, we use it for the first time as a way to scan through the IBE in order to study the growth mechanism of hydrogenated microcrystalline silicon using a SiH_4/H_2 chemistry. We find that at critical energies, a stepwise increase in the amorphous to microcrystalline transition thickness is observed, as detected by Real Time Spectroscopic Ellipsometry. The same energy thresholds (30 eV and 70 eV) are found to be very influential on the final surface morphology of the samples, as observed by Atomic Force Microscopy. These thresholds correspond to SiH_x~+ bulk displacement (30 eV) and H_x~+ (70 eV) surface displacement energies. A model is therefore proposed to account for the impact of these ions on the morphology of μc-Si:H growth.