Investigation of Si/CoSi2/Si(001) interfaces formed by high-dose Co implantation using HREM and image simulations

Abstract

Cobaltdisilicide has been the subject of much study, because of the good lattice matching with Si, its low resistivity, and the formation of atomically abrupt interfaces. Hetero-epitaxial Si/ CoSi2/Si structures are of interest due to their potential application as metal and permeable base transistors. We have synthesized mesotaxial CoSi2 films of aligned orientation by high-dose implantation of Co+ ions into Si (001) substrates followed by a high-temperature treatment of 30 minutes at 1000 °C. The Si wafers were implanted with 170 keV Co+ ions, with doses of 1 to 2 × 1017 Co+/cm2 , at an ion current density of 11 μA/cm2. The atomic structure of the CoSi2/ Si (001) interface has been investigated by high-resolution microscopy (HREM) combined with image simulations. The electronic properties of the CoSi2 films, such as the Schottky barrier height between the metal and the semiconductor, may be influenced by the atomic structure of the interface. Moreover, detailed knowledge of the atomic interface structure can give insight into mechanisms of silicide growth. Recently, Loretto et al. have shown that the structure of a CoSi2 /Si (001) interface grown by molecular beam epitaxy (MBE) is a 2×1 reconstruction of silicon dimers with bond length 0.23 nm, similar to the Si (001) 2×1 surface. This model (see fig. 1a) differs from that of Cherns et al. concerning NiSi2/Si (001), by the presence of an extra row of atoms at the interface. The additional Si atoms can form dimer chains, reducing the number of dangling bonds. This interface model projected along [110], is shown in Fig. 1a (see lower interface). The upper interface can be considered as a projection of the same structure along [10] .