Direct Solid State Phase Transformation from Co to Epitaxial CoSi2 in Co / Thin Ti / (100) Si Structure and its Application for Shallow Junction Formation

Abstract

ABSTRACTDirect epitaxial CoSi2 formation from Co, which is contrary to the reported silicidation process : Co→Co2 Si→CoSi→CoSi2, has been found during anneal of Co / Ti / (100) Si system. 2 nm thick Ti and 15 nm thick Co films were sputter deposited, and then annealed for 30 min at temperatures between 375°C and 900°C. At room temperature, the 2 nrm Ti immediately forms an amorphous Ti-Si-Co layer between the Co and Si. Epitaxial CoSi2 begins to form at 400°C, while the amorphous layer continues to act as both a Co diffusion retardant and Si diffusion suppressant even at 900°C. This retarded diffusion of Co reduces the growth rate of the CoSi2 over the entire temperature range studied. Superiority of the epitaxial to polycrystalline silicide has been demonstrated. In self aligned structures, an epitaxial CoSi2 film is formed by a single-step anneal without any overgrowth onto adjacent field oxide areas utilizing the amorphous diffusion controlling layer. A p+/n junction of 40 nm depth with reduced leakage and low ideality factor has been obtained by impurity diffusion from epitaxial CoSi2.