Plasma purification by ion cyclotron resonance for plasma source ion implantation doping of semiconductors

Summary form only given. Using Plasma Source Ion Implantation (PSII) to create the shallow source and drain structures required for next generation devices may be a necessity. A critical concern for the use of PSII in doping these next generation semiconductor devices is to avoid implanting contaminant ions. For example, future devices are predicted to require that heavy metal doses be kept less than 3/spl times/10/sup 9/ atoms per square centimeters. When doping semiconductors using conventional beam line accelerator technology, the implantation is very pure because bending the beam with a magnetic field very efficiently selects a single mass species. In order to provide a similar purity implantation for PSII a process utilizing ion cyclotron resonance for plasma purification prior to implantation is being investigated. In order to purify the plasma a DC magnetic field is imposed in the plasma and an RF electric field is imposed perpendicular to the magnetic field. If the frequency of the RF electric field is selected to be at the cyclotron frequency of a contaminant ion, the contaminant ion will gain energy efficiently and be diffused out of the plasma faster than noncontaminant ions, and its increased diffusion rate will be primarily perpendicular to the magnetic field. Once a contaminant ion is expelled from the plasma it is neutralized upon collision with a wall and is no longer an implantation hazard. We present simulation results showing necessary field strengths and uniformity for plasma purification, cleaning efficiency of the described system, and frequency/mass resolution of the method.