Ion energy distributions in plasma immersion ion implantation-theory and experiment

Much has been published recently stating the effectiveness of plasma immersion ion implantation (PIII) in producing ultra-shallow junctions (USJ). Although PIII is capable of producing USJ implants as effectively as conventional mass-analyzed ion implantation, there are several differences. One such difference, due to sheath dynamics and pulse characteristics, is that PIII implants always contain low energy components. Although such (shallower) components are not deleterious for USJ formation, there is much concern that they can be controlled repeatably. Others have developed sheath models which relate pulse current to ion energies, and have compared predicted currents to measurements of the total platen current. However, the total platen current includes contributions due to displacement currents (needed to create the high voltage negative pulse) as well as both plasma and secondary electron currents. We developed a Faraday cup embedded within the wafer platen which is capable of measuring the ion current alone. This ion current data, along with the platen voltage data has been be used to test and further refine the sheath model. The model was then used to predict the energy content of the ions, which was further tested by comparison with as-implanted SIMS profiles.