Dynamic measurements of optical emission during plasma immersion ion implantation

Abstract

Plasma immersion ion implantation (PIII) is characterized by applying short high voltage pulses to a substrate immersed in a low pressure plasma discharge. Compared to a more conventional experimental setup for glow discharge optical emission spectroscopy (GDOES) where sputtered atoms are detected, the PIII experiment is characterized by higher ion energies of the primary ions, lower pressures with a larger mean free path, shorter pulses and a higher relative energy density deposited by the secondary electrons emitted from the surface. Using time resolved optical emission spectroscopy (OES) during PIII high voltage pulses, detailed insights into the interactions of sputtered atoms, secondary electrons and the low pressure plasma discharge are possible. Thus, a direct excitation of the sputtered particles by the secondary electrons is highly unlikely due to the small cross-sections. However, a transient increased optical emission was observed with the maximum intensity about 20–80 μs after the end of the high voltage pulse. This delayed excitation of Ar I, Ar II and Me I lines scale with the secondary electron emission coefficient. Nevertheless, transient plasma excitations including long-living metastable states by secondary electrons could be probed in this setup.