Measurements and modeling of electron energy distributions in the afterglow of a pulsed discharge in BF3
Institute of Physics, University of Belgrade - POB 68, 11080 Belgrade, Serbia
2 Varian Semiconductor Equipment Associates - 35 Dory Road, GL-17, Gloucester, MA 01930, USA
3 Faculty of Transport and Traffic Engineering, University of Belgrade - Belgrade, Serbia
Accepted: 8 July 2011
In this paper we use experimental data (Radovanov S. and Godet L., J. Phys.: Conf. Ser., 71 (2007) 012014) for time-resolved electron energy distribution function in boron trifluoride (BF3) discharges together with cross-sections for electron excitation processes and attachment in order to explain electron dynamics in the pulsed plasma doping system. A Monte Carlo simulation (MCS) was used to perform calculations of the electron energy probability function (EEPF) in pulsed DC electric fields as found in practical implantation devices. It was found that in the afterglow, electric field in the plasma is not zero but still has a significant reduced electric field (E/N) albeit below the breakdown condition. Our analysis assuming free diffusion conditions in the afterglow led to the calculation of EEPF for a range of E/N corresponding to different afterglow times of a pulsed DC discharge. Calculated and experimental EEPF agree fairly well for a given set of cross-sections (see paper by Radovanov and Godet quoted above) and assumed initial distributions. In addition we have modeled the kinetics of production of negative ions in the afterglow as observed by experiment and found an increase in the production of negative ions in the early afterglow. Electron attachment in BF3 with 0.1% of F2 is a possible explanation for the observed rate of negative-ion production as predicted by our Monte Carlo simulation. However, the most likely cause for the increase in detected number density of ions is the collapse of the field-controlling electrons.
PACS: 52.20.-j – Elementary processes in plasmas / 52.20.Fs – Electron collisions / 52.65.Pp – Monte Carlo methods
© EPLA, 2011