Electrical behaviour associated with defect tails in germanium implanted silicon

In this study the impact of the defect tails generated by germanium implantation into n-type silicon wafers on the deep energy states, the doping profiles and mobilities, are investigated. 100 mm (100) silicon wafers with a base doping concentration of 3×10¹⁵/cm³ have been implanted with 80 keV germanium on the Danfysik DF1090 high current implanter using instantaneous current density of 5 μA/cm²-95 μA/cm², which correspond to power loading values of 0.4 and 7.6 W/cm² respectively. Channelling Rutherford Backscattering analysis of a wafer implanted with 1×10¹⁶ Ge/cm² and a dose rate of 80 μA/cm ² indicates a defect tail extending to 0.65 μm compared with 0.35 μm from a similar implant using 20 μA/cm². Deep Level Transient Spectroscopy (DLTS) measurements of samples implanted with 3×x10¹⁴ Ge/cm² followed by a regrowth anneal of 700°C for 20 mins reveal a high concentration of deep levels beyond the projected range of germanium of 58 nm at depths extending from 0.15 μm to depths greater than 0.4 μm. The main peak indicates a deep level at 0.36 eV. The increase in the dose rate from 5 μA/cm² to 95 μA/cm² is accompanied by a 5 times reduction of the 0.35 eV trap concentration. This difference could be attributed to the dynamic annealing effects during the implant using 95 μA/cm²