Low-temperature epitaxial Ni silicidation: the role of hyperthermal species

We present the results of Ni silicidation on a Si111 surface employing a mass-selected hyperthermal ion beam at 100 eV and discuss the reaction mechanism compared with the conventional Ni silicidation process. It is found that the Ni silicide formation using this technique is different from that achieved by conventional methods such as high-energy Ni-ion implantation or evaporation with thermal species. Namely, the Ni silicide phase formed at 230 degrees C using hyperthermal ions in this study is Ni-rich Ni2Si, in contrast to Si-rich disilicide NiSi2, ordinarily formed when high-energy Ni ions or thermal Ni beams react with Si at elevated temperatures. In addition, this layer is formed epitaxially on Si in spite of a low substrate temperature of 230 degrees C, while a polycrystalline Ni silicide layer is formed with conventional Ni-rich silicidation. This suggests that the reaction mechanism of the silicide formation with hyperthermal Ni particles is different from that using higher- or thermal-energy Ni particles. The atomic rearrangement induced by the thermal spikes most likely plays an important role in the Ni silicidation process employing hyperthermal species.