Influence of Beam-Extraction Structure on the Ion Energy for Ultra-Shallow Implantation

Ions extracted from a plasma source have an excess energy arising from the plasma potential besides the basic ion energy arising from the acceleration voltage that is supplied to the source chamber. Especially for very-low-energy ion beam the excess energy cannot be neglected. In this paper, a new formula is obtained on the basis of continuity principle of electric current that flows through plasma to be extracted as an ion beam. In consequence it is found that the plasma potential changes independently of the intensity of ion-beam current, but dependently on the ion-beam-extraction structure. Microwave ion source is studied in details as an example of ion source for practical use.