Control of Nanocrystalline Silicon Growth Phase and Deposition Rate through Voltage Waveform Tailoring during PECVD

International audienceThe use of Voltage Waveform Tailoring (VWT) that is the use of non-sinusoidal waveforms with a period equivalent to RF frequencies is shown to be effective in modifying the electric field distribution in a parallel plate, capacitively coupled laboratory plasma deposition reactor, and thus in changing the growth mode of silicon thin films from amorphous to nanocrystalline. The use of the VWT technique allows one to decouple the power injected into the plasma from the ion-bombardment energy at the film surface without changing any other deposition parameters, such as pressure or gas mixture. Material results are presented for an H2/SiH4 gas composition. A peaks type waveform increases the ion-bombardment energy at the RF electrode and reduces it at the substrate, resulting in more nanocrystalline growth. The use of a valleys-type waveform has the opposite effect, and results in more amorphous growth. We show the dependence of the process on silane dilution and pressure, including results on changes to the deposition rate when changing the excitation voltage waveform