Measurement of time-dependent sheath for the planar target in plasma source ion implantation

Summary form only given. In plasma source ion implantaion (PSII), the target is biased by successive negative voltage pulses with an intrinsic finite rise time to implant ions from plasma to target surface, resulting in a time-dependent sheath around target. In this work, the Langmuir probe was used to study the sheath motion around a planar target with various pulse conditions and plasma conditions in PSII. It was observed that the time-dependent sheath consisted of two parts: the ion matrix sheath development and the dynamic sheath motion. A new model for the ion matrix sheath development was proposed to explain the experimental results which showed discrepancies compared with Lieberman´s model (Stewart and Lieberman, 1991) and the computer simulation. The ion matrix sheath development was in proportion to square root of pulse rise rate over plasma density and also to square root of pulse rise time. The dynamic sheaths were faster than the ion acoustic speed after the pulse rise and eventually slowed down to approximately a third of ion acoustic speed.