Plasma oxidation of TaSix thin films

We have investigated the RF plasma oxidation at floating potential of tantalum silicides, TaSix (1.6 ⩽ x ⩽ 3.6), in the 300–800°C temperature range. Rutherford backscattering spectrometry and nuclear reaction analysis have been used to study the composition of samples and to determine the oxide growth kinetics. Whatever the initial silicide composition there are two different regimes in the oxide growth depending on the temperature. The transition temperature between these two regimes is about 550°C. However, both temperature and silicide stoichiometry play an important role in the nature of the grown oxides. The fact that the silicide is silicon enriched with respect to the stoichiometric composition of a disilicide (i.e. x 2) leads to the growth of a pure SiO2 film on the surface in the 300–800°C range. On the other hand, if the silicide is tantalum enriched (i.e x < 2) the nature of the oxide depends on the temperature: almost pure SiO2 for T < 550°C and an oxide mixture (Ta2O5-SiO2) in the 500–700°C range. It has also been evidenced that it is possible to grow a pure SiO2 film on the surface even if the silicide is Ta enriched provided that the temperature is high enough ( ∼ 800°C).