Dose rate dependence of residual defects in device grade Si/SiGe heterostructures formed by ion beam synthesis

The influence of germanium ion current density on the residual defects in ion implanted Si/SiGe heterostructures is investigated. Data from (100) silicon wafers implanted with 400 keV 9×10¹⁶ Ge⁺/cm² shows that both the nature and concentration profile of residual defects below the amorphised silicon surface layer are highly sensitive to the Ge⁺ current density. Dose rates in the range of 7.3×10¹² Ge⁺ /s.cm² and 1.5×10¹² Ge⁺/s.cm² corresponding to power loading of 0.47 W/cm² and 0.09 W/cm² respectively, were investigated in this study. The nature and concentration of the defects was investigated by Rutherford Backscattering Channelling analysis (RBS-c), cross section Transmission Electron Microscopy (xTEM) and Positron Annihilation Spectroscopy (PAS) in conjunction with anodic oxidation and wet etching. RBS-c indicates that by increasing the dose rate from 5 μA/cm² to 13 μA/cm² reduces the thickness of the amorphous layer from 550 nm to 350 nm. A further increase to 20 μA/cm² inhibits the formation of an amorphous layer due to dynamic annealing. This is associated with a significant increase in the depth profile of interstitial defects down to a depth of 800 nm. As in the case of interstitial defects, there is a considerable enhancement in the depth and concentration of open volume defects with increasing dose rate found by PAS analysis. For the highest dose rate open volume defects extend beyond 1.5 μm at a concentration in excess of 1×10¹⁶/cm². Post amorphisation with Si⁺ implantation removes all the Ge⁺ implant related defects leaving strain related defects and deep band of end of range defects