Formation of buried CoSi 2 layers with ion beam synthesis at low implantation energies

Abstract

The formation of Si/CoSi 2/Si heterostructures by high dose Co implantation has been studied for the implantation energy range of 30–200 keV. Various implantation and post-implantation annealing procedures were investigated in order to determine the conditions for producing the thinnest possible CoSi 2 layers. Layer thicknesses ranging from 70 nm at 200 keV to as thin as 18 nm at 30 keV were produced in both (100) and (111) oriented Si. For implantation energies < 70 keV, it was necessary to keep the annealing temperatures below 950°C in (100) Si — a restriction not encountered in (111) Si — to produce a continuous layer. The mechanism for this temperature dependence is discussed. Channeled implantation was also investigated as a technique to produce a thin buried layer at low energies, but comparison of such layers with typical random implants showed no improvement in heterostructure quality nor any apparent processing advantages. Finally, the suitability of the top Si layer of the heterostructures as a seed for epitaxial Si has been investigated with low pressure vapor phase epitaxy. The heterostructures were analyzed by Rutherford backscattering spectroscopy, ion channeling, cross section transmission electron microscopy and resistivity measurements.