New trends in PBII technology: industrial perspectives and limitations

Abstract

The two general specifications required for plasma-based ion implantation are low pressure large size plasmas and high voltage high current pulse generators. Due to the wide ion sheath expansion (up to a few tens of cm), large volumes of plasma are mandatory around the substrate. Multipolar discharges, which produce a peripheral ionization facing the substrate and can be easily scaled up, are well suited to PBII processing and begin to be widely used. However, hot filaments to sustain plasmas of reactive gases in multipolar magnetic field structures must be ruled out in favor of distributed electron cyclotron resonance (DECR) plasma sources. In order to produce the high voltage high current pulses 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, appear particularly well-adapted to fulfill most of the PBII requirements in terms of reliability, compactness, cost and safety. At the industrial level, a very great advantage of PBII over ion beam implantation lies in achieving sequential processing in the same reactor, such as cleaning, etching and deposition prior to, during, or after the implantation process. As examples, thermochemical processing can be performed via PBII with or without external independent heating. More generally, the combination of DECR plasmas and magnetron discharges in the same reactor opens new possibilities for complex treatments such as PBII/CVD (chemical vapor deposition) in DECR plasmas or PBII/PVD (physical vapor deposition) in hybrid DECR-magnetron reactors. However, the transfer of processes from the laboratory to industry is mainly limited to very specific and low energy applications. In fact, mass production using high voltage PBII processing requires production tools still under development. Due to huge secondary electron emission and sheath thickness above 100 kV pulse voltages, large volume reactors (a few cubic meters) on one hand, high power pulse supplies (100 kV–1000 A/100 MW) on the other hand, are mandatory for the rise of PBII at the industrial scale.