Inhibition of Crystal Growth during Plasma Enhanced Atomic Layer Deposition by Applying BIAS

In this study, the influence of direct current (DC) biasing on the growth of titanium dioxide (TiO₂) layers and their nucleation behavior has been investigated. Titania films were prepared by plasma enhanced atomic layer deposition (PEALD) using Ti(OiPr)₄ as metal organic precursor. Oxygen plasma, provided by remote inductively coupled plasma, was used as an oxygen source. The TiO₂ films were deposited with and without DC biasing. A strong dependence of the applied voltage on the formation of crystallites in the TiO₂ layer is shown. These crystallites form spherical hillocks on the surface which causes high surface roughness. By applying a higher voltage than the plasma potential no hillock appears on the surface. Based on these results, it seems likely, that ions are responsible for the nucleation and hillock growth. Hence, the hillock formation can be controlled by controlling the ion energy and ion flux. The growth per cycle remains unchanged, whereas the refractive index slightly decreases in the absence of energetic oxygen ions.