SYNTHESIS OF THIN BURIED COSI2 LAYERS BY LOW-ENERGY COBALT IMPLANTATION

The formation of Si/CoSi2/Si heterostructures by high-dose cobalt implantation was studied for the range of implantation energy 20-200 keV. Various implantation and post-implantation annealing procedures were investigated in order to determine the conditions for producing the thinnest possible CoSi2 layers. Layers as thin as 12 nm in (111) silicon and 18 nm in (100) silicon were produced with energies of 20 keV and 30 keV respectively. For implantation energies less than 70 keV, it was necessary to use annealing temperatures below 950-degrees-C in (100) silicon-a restriction not encountered in (111) silicon-to produce a continuous layer. The origin of this temperature dependence is discussed. In addition, the specific resistivity depends on thickness for CoSi2 layers less than 20 nm. The heterostructures were analyzed by Rutherford backscattering spectroscopy, ion channeling, cross-sectional transmission electron microscopy and resistivity measurements.