Dwell-time dependence of irradiation damage in silicon

The influence of the dose rate on the damage creation in silicon has been investigated by means of high current density focused ion beam (FIB) implantation. 70 keV Co and Ge ions with a current density of about 1 A/cm2 have been implanted into silicon at target temperatures in the range from room temperature to 420°C. The effective dose rate was varied between 1013 ions/cm2s and about 1019 ions/cm2s applying different pixel dwell times from 1 µs to 250 µs. The samples have been investigated using Rutherford backscattering / channeling combined with a special preparation technique, scanning electron microscopy, micro-Raman spectroscopy and reflectivity measurements. It have been found that at short dwell times at implantation temperatures of about 400°C the silicon remains crystalline after Co as well as Ge ion bombardment also in the limit of high doses while at long dwell times the crystal becomes amorphous. These studies of damage accumulation and dynamic annealing reveal that the characteristic time of defect annealing lies in the µs-range.