Modeling plasma immersion ion implantation under trapezoidal voltage pulses

Abstract

Summary form only given, as follows. Motivated by previous works, the present paper pictures plasma immersion ion implantation for voltage pulses with finite rise and fall times from the point of view of a parallel-plane diode in which all the parameters of the ion flow (charge density, ion velocity, voltage across the sheath, electric field on the target) are consistent with the space-charge-limited regime. The sheath edge uncovering new ions is thought of as an ion emitting electrode that moves outward from the collector subjected to negatively pulsed voltages, whereby the time-dependent behavior of the diode is examined as a sequence of steady states that the system traces following the Child law at each instant of time. The emitted from the moving virtual electrode is then related to the convection collected on the target through a delay time that properly accounts for the transit time of the ions across the sheath. Verification of the continuity of the total current expressed here as the sum of the convection and the displacement currents indicates that such modelling becomes more realistic as the time scale of the ion motion gets shorter than the characteristic times of the applied voltage waveform.