Single and double buried epitaxial metallic layers in Si prepared by ion implantation

Abstract

In recent years, heteroepitaxial structures of CoSi 2/Si and Si/CoSi 2/Si have become an important topic of fundamental studies, as well as of novel device applications. The usual method for preparation of such structures is deposition of Co or CoSi 2 with techniques such as molecular beam epitaxy (MBE). Ion beam synthesis (IBS) is another attractive method which has been developed recently. With this new technique, heteroepitaxial surface and buried CoSi 2 layers with thicknesses from 160 to 1100 Å have been formed successfully. RBS, channeling, cross-sectional TEM, Mössbauer spectroscopy and X-ray rocking curve measurements have been used to study the thickness, the crystalline quality, the abruptness of the interfaces, the chemical phase, the strain and the orientation of both the surface and buried CoSi 2 layers. The results show that the quality of surface and buried CoSi 2 layers formed by IBS is as good as those formed by MBE. The measured values for the strain are found to be far below the value expected for pseudomorphic layers, and show no clear correlation with the layer thickness. On the other hand, we observed a remarkable correlation between the thickness of the buried layer and its orientation: the orientation ranges from 100% type A orientation (parallel with the Si substrate) for a thick layer (thicker than 360 Å) to as much as 70% type B (antiparallel with the Si substrate) for thinner layers. This phenomenon is interpreted as an equilibrium between two driving forces. Recently, we made the first double heterostructures by ion implantation at two different energies. After annealing, a Si/CoSi 2/Si/CoSi 2/Si-substrate structure with two buried CoSi 2 layers was obtained. The thinnest (160 Å) has a pure type B orientation while the thickest layer (600 Å) has pure type A orientation. This result fully fits in the thickness dependence of the orientation we found for single CoSi 2 layers.