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 Å s^-1 on one electrode and an etching rate of 1.2 Å 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.