Exact ion energy in plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is used in various industrial fields such as surface modification of materials and sterilization of disease spores. Recently the technology has become utilized for the applications, in which rather lower ion energy is required, such as shallow ion implantation into cutting-edge semiconductor devices of 3 D structure, i.e. so-called Thin FET as well as low temperature crystallization of sputter-deposited film. In the near future the applications will need low ion energy from 500 eV for the Thin-FET implantation to 50 eV for the low temperature crystallization. The ion energy in PIII is, strictly speaking, given by the summation of the pulse bias voltage and the plasma potential. When the bias voltage was as high as several kV for the surface modification of materials, the plasma potential, which is several tens of voltage in usual industrial plasma, could be neglected. However, for the above-mentioned low energy applications, the plasma potential has an important role to determine the ion energy. Until now, in order to determine the ion energy the plasma potential that was obtained when the bias voltage was not supplied was used. In this study we found that plasma potential changed due to the bias voltage for implantation, too. Resultantly, we obtained the exact ion energy for low-energy PIII by correcting the plasma potential with the bias current.