STUDY OF THE DIFFUSION PATH DURING THE LATERAL GROWTH IN THE SALICIDE PROCESS

Self-aligned formation of silicides allows selective formation of MSi2 on poly- or mono-crystalline Si and is typically used for gate, source and drain metallization. Under certain conditions lateral growth of a parasitic layer is observed during silicide formation. For example, TiSi2 formation under Ar atmosphere or in a vacuum results in a thin conductive layer on SiO2, which can expand over several microns in the neighbourhood of Si. In this paper results of experiments with WSi2 and TiSi2 formation will be presented. Different conditions have been investigated with respect to lateral growth: anneal under vacuum, Ar, N2 or different dilutions of NH3, or deposition of an encapsulation layer on top of the metal prior to the anneal. Results of both silicides will be compared. Based on these experiments a model will be proposed for the fast diffusion which causes the lateral growth.