Oxidation of silicide thin films: TiSi₂

The oxidation of TiSi2 thin films on polysilicon illustrates extreme examples of behavior. At 700°C in wet O2, one observes the formation of titanium oxide and the simultaneous rejection of silicon towards greater depths, away from the oxidized surface layer. At 1100°C with the same type of sample, one observes the growth of a metal-free layer of SiO2, the formation of which required not only the use of the whole available polysilicon, but the reduction of the initial disilicide to a lower silicide, mostly TiSi. These observations are discussed in terms of previous results obtained either with TiSi2 or with other silicides, and in terms of what is known about the thermodynamics of the system titanium oxide-silicon oxide.