Reaction mechanism of cobalt with silicon dioxide

Abstract

The reaction mechanism of thin cobalt (Co) films with silicon dioxide (SiO2) substrate under rapid thermal annealing conditions has been investigated. Reaction of thin cobalt film (12.5 nm) with a SiO2 substrate is observed in an inert ambient (N2) and in vacuum (∼-8Torr). The reaction is manifested by the formation of craterlike depressions on the SiO2 substrate and by the presence of a Co2SiO4 reaction product determined by transmission electron microscopy diffraction patterns. Much less damage is observed with no reaction product observed if the samples are annealed in a forming gas ambient (90% N2/10% H2), the cobalt film is much thicker (150 nm), or the cobalt film is in situ cleaned (e.g., 5 min in 400 °C, forming gas ambient) prior to annealing in either inert or vacuum ambient. It is proposed that the presence of oxygen is required in order to initiate the reaction between cobalt and SiO2. The source of the oxygen contaminant, in our studies, is the oxygen on the surface of the cobalt film. The proposed reaction is 2 Co+SiO2+2〈0〉)→Co2SiO4 where 〈0〉 represents oxygen contaminant at the surface. © 1996 American Institute of Physics.