Ion implantation by plasma immersion: interest, limitations and perspectives

Plasma-based ion implantation (PBII) is a recent method to implant ions into materials for modifying surface properties. Negative high voltage pulses are applied to the substrate to extract ions from the plasma and accelerate them directly onto the substrate surface. The main advantages of PBII over ion beam implantation are its simplicity for processing large surfaces or three-dimensional objects and the possibility of preparing surfaces in situ prior to the implantation process. The two general specifications required for PBII are low pressure, large size plasmas and high voltage–high current pulse generators. Multipolar discharges excited by distributed electron cyclotron resonance, which can operate with reactive gases and can be easily scaled up, are thus well adapted to the PBII process. In order to produce the high voltage–high current pulses with rise and fall times of the order of the inverse ion plasma frequency necessary for PBII processing, generators using pulse transformers, where the voltage at the primary is provided by transistor switches and where the energy is stored at a low voltage level, have been developed. Then, before discussing the various limitations of the process, PBII in plasmas is illustrated through few selected examples.