Scanning tunneling microscopy study of the interfacial structure of nickel silicides

Abstract

The growth of ultrathin silicide ͑ϳmonolayer͒ has been studied by scanning tunneling microscopy. Ni atoms react with the Si͑111͒-7ϫ7 surface to form clusters at room temperature. With increasing annealing temperature, they gradually coalesce and form monolayer islands surrounded by ͱ19ϫͱ19 ring structures. The surface structure shows ͱ3ϫͱ3-R30°at 400°C and 2ϫ2 at 600°C. The latter structure is a new finding for the Ni/Si system. It is suggested that the transformation of the surface structure on the monolayer island can be related to a change of the interfacial structure.

Formation of two-dimensional silicide on Ni(100) surface

“…19 -R23.4°, and (1 × 1)-RC phases on a Si(111) surface, [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and ´n 2 and 2 2-R45°p hases on a Si(100) surface 11,[21][22][23] have no analogous bulk silicide. Although the lattice mismatch between Si and bulk NiSi 2 is negligible (−0.44%), no epitaxial 2-D silicides corresponding to the low-index face of NiSi 2 or other bulk silicides are formed on Si substrates.…”

“…In contrast to Si on Ni, Ni-induced reconstructions on Si substrates do not have a uniform 2-D silicide covering the entire surface with a single phase. [10][11][12][13][14]16,17) This fact is due to the large diffusion of Ni into the bulk Si which prevents a flat 2-D silicide forming on Si substrates, 54) and before a uniform 2-D silicide is completed, deposited Ni atoms diffuse into the bulk Si and precipitate more stable 3-D silicides, which induce inhomogeneity of the surface layer.…”

“…19 -R23.4°, and (1 × 1)-ring cluster (RC) phases. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] These surface silicides are thought to be intermediate states before the formation of thick epitaxial silicides. It has been reported that ´n 2 and 2 2-R45°phases form on a Si(100) substrate depending on the Ni coverages and substrate temperatures.…”