The influence of Ti and TiN on the thermal stability of CoSi2.

Abstract

ABSTRACTIn this work, AFM and sheet resistance measurements are used to characterize the thermal stability of thin CoSi2 films. We were particularly interested in the influence of different multilayer structures on the topography and surface roughness. Four different multilayer structures (Co/Si, TiN/Co/Si, Ti/Co/Si and Co/Ti/Si) were investigated. Thermal degradation of CoSi2 formed from a standard Co/Si structure is found to have an activation energy of about 4.2 eV, independent of layer thickness (in agreement with previous results by Alberti et al.). A TiN capping layer is shown to improve the thermal stability. However, if the TiN layer is too thick (e.g. 50 nm), a new failure mode is observed: although the TiN prevents grain boundary grooving of the silicide, the thermal stress induced by the TiN causes the CoSi2 layer to crack. For a Ti capping layer, a strong increase of the thermal stability of the CoSi2 layer is observed, even if the Ti capping layer is removed by a selective etching step after the first RTP annealing. The presence of a very thin Ti-O-N containing layer on the CoSi2surface seems to strongly decrease surface diffusion and in this way reduce the tendency for grain boundary grooving.