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

CaF₂-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 ≃1000 Å 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. [ABSTRACT FROM AUTHOR]