Stability of NiSi2 and CoSi2 in contact with their free metal

Rutherford backscattering has been used to study metal/disilicide thin-film interactions for Ni and Co. Upon heating, the metal reacted with disilicide to produce the phase M2Si in both cases. On further heating the M2Si itself reacted with the disilicide to form MSi. In the case of Co it was found that after all the metal had been converted to CoSi in this way, the reaction stopped. However, with Ni the disilicide substrate continued to dissociate into NiSi and Si even after all the original Ni had reacted to form NiSi. The stability of NiSi2 under various conditions was investigated and it appears that twin requirements of a crystalline silicon substrate on which the excess Si can regrow and nucleation sites in the form of NiSi are necessary in order to induce dissociation.