Energy distribution and depth profile in BF₃ plasma doping

Plasma doping (PD) is intrinsically different from beam-line doping (BD), as there is no mass filtering and the ion impact angle depends on the target geometry and plasma conditions. There are several ways to alter the impact energy of the incident ions and consequently the dopant depth profile when a BF₃ plasma is used, because the plasma consists of ion species with different masses, compositions, and charge states. The rise and fall times of the sample voltage pulse also contribute to the overall energy distribution, since a long rise or fall time will increase the low-energy component. In this work, a particle-in-cell model is employed to simulate BF₃ PD into silicon under typical plasma doping conditions. The energy distributions of the implanted B and F, as well as the effects of the rise/fall time and other factors are discussed. The PD profiles are compared to BD depth profiles acquired by the TRIM simulation code. Our results reveal that the plasma conditions and pulse shape can be altered to obtain the desired B depth profile. In addition, PD gives rise to a low-energy surface component that is larger for a longer rise and fall time.