Modeling and experiments of waveform effects on oxide charging in plasma immersion ion implantation [MOS ICs]

An analytical model of the time-dependent currents of a plasma allows the determination of the physical mechanisms and dependencies of charging damage in Plasma Immersion Ion Implantation (PIII). From the model, we determine that the plasma requires several ms to equilibrate after the application of an implantation voltage pulse. Although the individual pulses only change the surface potential by a fraction of a volt, the long equilibration time means that the pulse repetition rate perturbs the time-averaged surface potential. A physical relation describing the dependence of the time-averaged surface potential on plasma and voltage bias parameters predicts that a shorter pulse width, lower electron temperature, and rectangular pulse shape maximizes the allowable implantation rate and minimizes the charging damage. For a given pulse shape and plasma condition, a maximum pulse repetition rate exists. Beyond this threshold frequency, the oxide fails because the oxide field exceeds its breakdown value. Experimental results corroborate the simulation's predictions, showing the dependence of the pulsing repetition rate on charging damage.