Electrical characteristics of ultrashallow p+/n junction formed by BF ₃ plasma doping and two-step annealing process

We have investigated ultrashallow p+ n junctions formed by BF₃ plasma doping. Conventional one-step annealing processes such as rapid thermal annealing or excimer laser annealing (ELA) are not effective methods for high activation of boron. Furthermore, it is known that fluorine can retard dopant activation. In order to reduce fluorine concentration, we propose additional preannealing at 600°C for 10 min followed by ELA. This process dramatically improved the boron activation ratio, while maintaining the same junction depth. The improvement of dopant activation is attributed to significant out-diffusion of fluorine which in turn enhances activation of boron during ELA.