CoSi2 nanohexagons buried in silicon substrates. Effects of the orientation of the Si host and kinetics of nanoplate formation

G. KELLERMANN; L.G. MONTORO; P.C. DOS SANTOS CLARO; L.J. GIOVANETTI; L. ZHANG; F.G. REQUEJO; A.J. RAMIREZ; A.F. CRAIEVICH

Cordoba

Congreso; I Reunión Latinoamericana de Cristalografía IX Reunión Anual de la Asociación Argentina de Cristalografía; 2013

Asociación Argentina de Cristalografía

We have previously described a simple method for obtaining thin hexagonal CoSi2 nanoplates buried in Si host single crystals. In this procedure a flat Si(001) wafer is covered with a Co-doped SiO2 thin film and then subjected to a high temperature isothermal annealing [1]. We demonstrated that Co atoms initially embedded in the SiO2 thin film diffuse into the Si crystal and promote the formation of buried CoSi2 nanoplates. The thin CoSi2 nanoplates exhibit a hexagonal lateral shape and are parallel to and coherent with the {111} planes of the host crystal. We have performed additional studies of the same process using Si substrates with three different orientations of their external surface, namely Si(001), Si(011) and Si(111), in which similar Co-doped SiO2 thin films were deposited. Our TEM results show that CoSi2 platelets with similar features are formed either in Si(001), Si(011) and Si(111) substrates subjected to equivalent thermal annealing. Regardless the Si surface orientation, the lattices of the hexagonal CoSi2 nanoplates are coherent with and parallel to crystallographic planes of the Si{111} form. Our GISAXS results demonstrate that the sizes of the CoSi2 nanohexagons are functions of the orientation of the external surface of the Si substrate, their thickness varying from 2.8nm for Si(001) up to 5.7 nm for Si(111). Finally, in situ GISAXS measurements at high temperature yielded the time dependence of the number density of CoSi2 platelets. Our results also indicate that the atomic diffusion of Co atoms into de Si crystals is, in all the studied cases, a fast process (lasting only a few seconds at T=750C), which quickly leads to CoSi2 platelets with nearly time invariant final sizes. Work supported by LNLS, LME-LNNano, CNPq and FAPESP, Brasil; ANPCYT and CONICET, Argentina [1] Kellermann G. et al, Appl. Phys. Lett. Vol.100 (2012) 063116.