Numerical investigation of plasma recovery in plasma source ion implantation

Experimental investigation of plasma recovery during the pulse-off time in plasma source ion implantation

“…However, it is also known that the plasma recovery time does not obey the linear dependency on the sheath thickness when the sheath thickness at the switch-off time exceeds 7 cm. According to previous work [8], this reduction of the plasma recovery time for large sheaths is related to the propagation of a compression wave in non-uniform plasma with ion drift. In the experiments, however, the propagation of the compression wave is not clearly observed, although the measured recovery times for large sheaths are in good agreement with those obtained from the simulations.…”

“…3 that the plasma recovery time depends on the sheath thickness at the switch-off time regardless of the amplitude and width of the applied pulse if the changes of the sheath thickness with the pulse characteristics are properly considered. The dashed straight line indicates the theoretical value from an earlier study [8], i.e. 5 s/u B , where the Bohm speed is calculated as 3175 m/s for argon plasma with an electron temperature of 4.2 eV.…”

“…The vertical error bars indicate when the electron saturation currents reach 99.5% (lower error bar) to 100% (upper error bar) of their pre-pulse levels for various experimental conditions. The plasma recovery time obtained by the numerical simulations [8] for various voltages and pulse-on times are also plotted in the figure.…”

“…Among the theoretical and numerical studies on the recovery process of a plasma sheath during the pulse-off time [5,7,8], recent numerical simulations considering realistic plasma density and ion velocity profiles showed that the plasma recovery time could be determined by the time required for a compression wave to reach the position of the sheath edge at the pulse-off time [8]. They reported that the characteristic time for the plasma recovery process is almost linearly proportional to 5 s/u B for small sheaths, where u B and s are the Bohm speed and the sheath thickness at the switch-off time, respectively.…”

“…Open symbols: The plasma recovery times obtained from the fluid simulations[8] under various operating conditions. Dashed line: Theoretical prediction of the plasma recovery time, expressed as 5 s/u B , where the Bohm speed is calculated for argon plasma with an electron temperature of 4.2 eV.…”