Thermal stability of Ni silicide films on heavily doped n and p Si substrates

Electrical and structural properties of Ni silicide films formed at various temperatures ranged from 200 °C to 950 °C on both heavily doped n⁺ and p⁺ Si substrates were studied. It was found that surface morphology as well as the sheet resistance properties of the Ni silicide films formed on n⁺ and p⁺ Si substrates at the temperatures higher than 600 °C were very different. Agglomerations of Ni silicide films on n⁺ Si substrates begin to occur at around 600 °C while there is no agglomeration observed in Ni silicide films on p⁺ Si substrates up to a forming temperature of 700 °C. It was also found that the phase transition temperature from NiSi phase to NiSi₂ phase depend on substrate types; 900 °C for NiSi film on n⁺ Si substrate and 750 °C for NiSi film on p⁺ Si substrate, respectively. Our results show that the agglomeration is, especially, important factor in the process temperature dependency of the sheet resistance of Ni silicides formed on n⁺ Si substrates.