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

Abstract

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/spl times/10/sup 16/ Ge/sup +//cm/sup 2/ shows that both the nature and concentration profile of residual defects below the amorphised silicon surface layer are highly sensitive to the Ge/sup +/ current density. Dose rates in the range of 7.3/spl times/10/sup 12/ Ge/sup +//s.cm/sup 2/ and 1.5/spl times/10/sup 12/ Ge/sup +//s.cm/sup 2/ corresponding to power loading of 0.47 W/cm/sup 2/ and 0.09 W/cm/sup 2/ 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 /spl mu/A/cm/sup 2/ to 13 /spl mu/A/cm/sup 2/ reduces the thickness of the amorphous layer from 550 nm to 350 nm. A further increase to 20 /spl mu/A/cm/sup 2/ 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 /spl mu/m at a concentration in excess of 1/spl times/10/sup 16//cm/sup 2/. Post amorphisation with Si/sup +/ implantation removes all the Ge/sup +/ implant related defects leaving strain related defects and deep band of end of range defects.