Investigation of concurrent flow of nitrogen and oxygen for the oxidation of cerium to cerium oxide films

Silicon-based metal-oxide-semiconductor (MOS) device was fabricated and investigated using cerium oxide (CeO₂) films as the high dielectric constant passivation layers, which were produced by introducing a post-sputter oxidation process in a nitrogen infused oxygen ambient at 800ºC onto the direct current (DC) sputtered cerium films. Formation of cubic fluorite CeO₂ phases along with an increase in crystallite size was obtained with the increase on nitrogen gas flow rate from 0 to 0.7 slm in the nitrogen infused oxygen ambient. Although the implementation of nitrogen gas flow rates has improved densification of CeO₂ films as well as impeding the growth of the silicon dioxide interfacial layer, bandgap narrowing happened when the flow rate of the nitrogen gas increased beyond/at 0.5 slm, which could be associated with the presence of larger amount of nitrogen ions in the samples, resulting in an overlapping of the nitrogen 2p states and O2p states, and hence reducing the bandgap width. In comparison, CeO₂ film subjected to post-sputter oxidation in 0.3 slm nitrogen gas flow rate could be the optimum parameter to be considered for further investigation in future work.