Improving the thermal stability of nickel monosilicide thin films by combining annealing with the use of an interlayer and a capping layer

The authors investigated the effects of preannealing a 2-nm-thick Pd interlayer and a 20-nm-thick TiN capping layer on the electrical and thermal stability of nickel silicides as a function of the annealing temperature. The preannealed samples (prepoly-Si) produce lower sheet resistances compared to the samples without preannealing. For the preannealed samples, NiSi remains stable up to 600 °C. Transmission electron microscopy results show that the preannealed samples have a higher resistance against layer inversion. The addition of a Pd interlayer at the Ni film/prepoly-Si interface increases the formation temperature of NiSi₂ to 900 °C. The use of the capping layer on the Pd-interlayered prepoly-Si samples improves the electrical and morphological stabilities of NiSi. The possible mechanisms for the preannealing and interlayer-induced improvement of the thermal stabilities of the Ni-silicide samples are discussed in terms of grain growth and simple thermodynamic relations.