Formations and morphological stabilities of ultrathin CoSi₂ films

In this paper we investigate the formations and morphological stabilities of Co-silicide films using 1-8-nm thick Co layers sputter-deposited on silicon (100) substrates. These ultrathin Co-silicide films are formed via solid-state reaction of the deposited Co films with Si substrate at annealing temperatures from 450 ℃ to 850 ℃. For Co layer with a thickness no larger than 1 nm, epitaxially aligned CoSi₂ films readily grow on silicon (100) substrate and exhibit good morphological stabilities up to 600 ℃. For Co layer thicker than 1 nm, polycrystalline CoSi and CoSi₂ films are observed. The critical thickness below which epitaxially aligned CoSi₂ film prevails is smaller than the reported critical thickness of Ni layer for epitaxial alignment of NiSi₂ on silicon (100) substrate. The larger lattice mismatch between CoSi₂ film and silicon substrate is the root cause for the smaller critical thickness of the Co layer.