Plasma-immersion ion implantation

Plasma-immersion ion implantation (PIII) or pulsed-plasma doping (pulsed PIII) is a surface modification technique of extracting the accelerated ions from the plasma by applying a high voltage pulsed DC or pure DC power supply and targeting them into a suitable substrate or electrode with a semiconductor wafer placed over it, so as to implant it with suitable dopants. The electrode is a cathode for an electropositive plasma, while it is an anode for an electronegative plasma. Plasma can be generated in a suitably designed vacuum chamber with the help of various plasma sources such as Electron Cyclotron Resonance plasma source which yields plasma with the highest ion density and lowest contamination level, helicon plasma source, capacitively coupled plasma source, inductively coupled plasma source, DC glow discharge and metal vapor arc(for metallic species). The vacuum chamber can be of two types - diode and triode type depending upon whether the power supply is applied to the substrate as in the former case or to the perforated grid as in the latter.

In a conventional immersion type of PIII system, also called as the diode type configuration, the wafer is kept at a negative potential since the positively charged ions of the electropositive plasma are the ones who get extracted and implanted. The wafer sample to be treated is placed on a sample holder in a vacuum chamber. The sample holder is connected to a high voltage power supply and is electrically insulated from the chamber wall. By means of pumping and gas feed systems, an atmosphere of a working gas at a suitable pressure is created.

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