Modeling of incident particle energy distribution in plasma immersion ion implantation

Plasma immersion ion implantation is an effective surface modification tech nique. Unlike conventional beam-line ion implantation, it features ion acce leration/implantation through a plasma sheath in a pulsed mode and non-line -of-sight operation. Consequently, the shape of the sample voltage pulse, e specially the finite rise time due to capacitance effects of the hardware, has a large influence on the energy spectra of the incident ions. In this a rticle, we present a simple and effective analytical model to predict and c alculate the energy distribution of the incident ions. The validity of the model is corroborated experimentally. Our results indicate that the ion ene rgy distribution is determined by the ratio of the total pulse duration to the sample voltage rise time but independent of the plasma composition, ion species, and implantation voltage, subsequently leading to the simple anal ytical expressions. The ion energy spectrum has basically two superimposed components, a high-energy one for the majority of the ions implanted during the plateau region of the voltage pulse as well as a low-energy one encomp assing ions implanted during the finite rise time of the voltage pulses. Th e lowest-energy component is attributed to a small initial expanding sheath obeying the Child-Langmuir law. Our model can also deal with broadening of the energy spectra due to molecular ions such as N-2(+) or O-2(+), in whic h case each implanted atom only carries a fraction (in this case, half) of the total acceleration energy. (C) 2000 American Institute of Physics. [S00 21-8979(00)00323-6].