Growth of CoSi2 on Si(001) by reactive deposition epitaxy

Abstract

Ca F 2 -structure CoSi2 layers were formed on Si(001) by reactive deposition epitaxy (RDE) and compared with CoSi2 layers obtained by conventional solid phase growth (SPG). In both sets of experiments, Co was deposited by ultrahigh-vacuum magnetron sputtering and CoSi2 formed at 600°C. However, in the case of RDE, CoSi2 formation occurred during Co deposition while for SPG, Co was deposited at 25°C and silicidation took place during subsequent annealing. X-ray diffraction pole figures and transmission electron microscopy results demonstrate that RDE CoSi2 layers are epitaxial with a cube-on-cube relationship, (001)CoSi2‖(001)Si and [100]CoSi2‖[100]Si. In contrast, SPG films are polycrystalline with an average grain size of ≃1000Å and a mixed 111∕002∕022∕112 orientation. We attribute the striking difference to rapid Co diffusion into the Si(001) substrate during RDE for which the high Co∕Si reactivity gives rise to a flux-limited reaction resulting in the direct formation of the disilicide phase. In contrast, sequential nucleation and transformation among increasingly Si-rich phases—from orthorhombic Co2Si to cubic CoSi to CoSi2—during SPG results in polycrystalline layers with a complex texture.