MORPHOLOGICAL INSTABILITIES OF NICKEL AND COBALT SILICIDES ON SILICON

The morphological instability of bilayers of NiSi, or CoSi2, on polysilicon has been investigated as a function of the thickness of the silicide, the presence of alloying additions and the intial oxidation of the silicide layer. The effect of Ir additions in enhancing the stability of the bilayers and the formation of NiSi2 confirms the expectation that the morphological instabilities and the nucleation of NiSi2 are dictated by surface energy effects (capillarity). Stresses may play a role in the initial step of the process which ultimately leads to a nearly complete inversion of the positions of the silicide and polysilicon layers. However, it is quite certain that the main driving force is the change in grain boundary energy of the polysilicon which starts with very small grains to begin with and ends up, at a different location, with much bigger grains.