Application of Plasma-Based Ion Implantation (PBII)
The technique of PBII has been developed in an effort to obtain increased ion current densities and therefore to achieve a substantial reduction in implant time as well as to avoid the line-of-sight limitation inherent to the conventional beam line ion implantation process. The efficiency of the PBII is superior to that of the standard implantation process, particularly for low energy, high dose implants.
In PBII a component is immersed in a processing plasma discharge containing the desired species, and negative high-voltage pulses are applied directly to the component. Ions are extracted from the plasma and are implanted into the material’s surface.
The ion beam current density depends on the plasma parameters and the bias voltage and is of the order of 1 – 10 mA/cm2. A pulsed high voltage is used to reduce substrate heating as well as to control charging. Typical pulse lengths are in the range of 2 to 100 µs at frequencies of a few 100 Hz up to 3 kHz. The substrate temperature can be controlled by varying the implant parameters, and may range from room temperature to 600°C without additional heating. Self-regulating charge control achieved by the alternating attraction of ions and electrons enables one to process not only conductive, but also insulating surfaces.
Another feature of PBII is the possibility to combine implantation and deposition processes. In comparison to a single deposition, the simultaneous deposition and ion implantation can improve the hardness of the material’s surface and the adhesion between the deposited layer and the substrate due to mixing effects.