Ion energy distributions measured inside a high-voltage cathode in a BF_3 pulsed dc plasma used for plasma doping: Experiments and ab initio calculations

摘要

The purpose of this paper is the characterization of a plasma-doping system in BF_3. Energy distributions (IEDs) of boron ions crossing a high-voltage sheath (up to 1 kV) are measured in a BF_3 plasma under different experimental conditions. It is demonstrated that relative percentages of boron ions reaching the cathode and IED shapes are governed by the number of collisions inside the sheath. Heavy molecular ions (B_2G + _5, B_2F+ _3) are dissociated inside the sheath and light boron ions (B_2F+, B_2F+_ 3) are created. Based on experimental results and ab initio calculations of boron ion structures, the mechanisms occurring in the sheath are discussed. Furthermore, the charge exchange cross-section between BF_3 + and BF_3 is estimated to be 8.8 × 10~(-19) m2.