The Annealing Time and Temperature Dependence of Electrical Dopant Activation in High-Dose BF2 Ion Implanted Silicon

The electrical dopant activation of high-dose 49BF2 ion implanted layers was investigated as a function of annealing time and temperature using rapid thermal annealing (RTA) and furnace annealing (FA). Fast recrystallization using RTA produces low sheet resistance, and prolonged annealing at low temperatures causes electrical dopant deactivation. The deactivation was controlled by a diffusion limited process with an activation energy (Ea) value of 3.46 eV, wh ich is equal to the Ea value of boron diffusion in the amorphous region that regrows to a single crystal. RTA yields low sheet resistances compared with FA, because RTA minimizes not only the redistribution of fluorine atoms in the amorphous region during the recrystallization, but also the electrical dopant deactivation during the time the wafer is cooling. H igh dose 49BF2 ion implantation 1'2 is generally used in the manufactur ing of very large scale integration (VLSI) to form the p+-source/drain junctions of metal oxide semicon-ductor field effect transistors (MOSFET's). The scaling down of electric device dimensions, wh ich is a continuing trend of VLS I device design, requires shallower junctions and higher doping levels. In order to fo rm shal low junc