Electrode-selective deposition/etching processes using an SiF4/H2/Ar plasma chemistry excited by sawtooth tailored voltage waveforms

We report on the electrode-selective deposition and etching of hydrogenated silicon thin films using a plasma enhanced chemical vapour deposition process excited by sawtooth-shaped tailored voltage waveforms (TVWs). The slope asymmetry of such waveforms leads to a different rate of sheath expansion and contraction at each electrode, and therefore different electron power absorption near each electrode. This effect was employed with an SiF4/H2/Ar plasma chemistry, as the surface processes that result from this gas mixture depend strongly on the local balance between multiple precursors. For a specific gas flow ratio, a deposition rate of 0.82 A s−1 on one electrode and an etching rate of 1.2 A s−1 on the other were achieved. Moreover, this deposition/etching balance is controlled by the H2 flow rate, which limits the deposition rate at low flows. When the H2 injection is sufficiently high, the processes are then limited by the dissociation of SiF4, and the relative rate of the surface processes on the two electrodes are reversed, i.e. a higher net deposition rate is observed on the electrode where the fast sheath contraction occurs due to the electronegative character of the plasma.