Temperature and energy dependence of ion-beam synthesis of epitaxial Si/CoSi2/Si heterostructures

The formation of buried CoSi2 layers by high-dose Co+ implantation into Si depends sensitively on the implantation temperature. Continuous buried epitaxial layers are only obtained at implantation temperatures above ∼300 °C. At temperatures below ∼200 °C, the implanted Si amorphizes, and the Co profile appears shifted towards the surface by about 250 Å compared to implantations performed above 300 °C, such that no buried layers are formed. A larger sputtering yield of the amorphous than the crystalline Si and a larger mean projected range of the implanted Co+ ions in single-crystalline Si seem to be responsible for the observed shift. For sputtering yields of 100- and 200-keV Co+ ions, we obtained values of Y=2.0±0.1 at room temperature and Y=1.7±0.1 at 350 °C. Implantations with energies ≤50 keV in (100) Si and subsequent annealing yield CoSi2 precipitates or layers at the surface, but not buried layers. The growth of rhombohedral precipitates in (100)Si aggravates the formation of very thin buried silicides. The minimum thickness of buried epitaxial silicides in (100)Si produced by high-dose implantations seems to be ∼400 Å, which is significantly larger than the minimum thickness in (111)Si (∼200 Å). Rapid thermal annealing leads to lower specific electrical resistivity values (13 μΩ cm) than conventional furnace annealing. Rutherford backscattering, He+-ion channeling, transmission electron microscopy, and sheet resistivity measurements were employed to characterize the implanted samples.