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Processes of plasma immersion ion implantation have been analyzed numerically using a one-dimensional self-consistent PIC-MCC model.The behaviors of ions and electrons between the processed target and source plasma were simulated when a short, high negative-voltage pulse with two different waveforms was imposed on the target.Simulation results showed that the electron-neutral ionization collisions played a significant role in determining the ion and electron densities when the pulse rise time is extremely short, comparable to the inverse of the electron plasma frequency.It was also found that a reverse electric field formed next to the plasma source when the pulse with a rectangular waveform was applied, whereas similar reverse field did not appear if the pulse had a trapezoidal waveform.The pulse rise time is a critical factor for determining the energy distribution of implanted ions.Implantation efficiency benefits from shorter pulse rise time.