In negative-ion implantation, the surface charging votage of isolated electrodes or insulators implanted with negative ions saturates within a quite low voltage as low as_-~+ several volts. In implantation into an isolated electrode, the incoming negative charge of negative ions is easily compensated for by the outgoing negative charge of secondary electrons having an energy of over several electron volts, which results in the eletrode being slightly positively-charged. In implantation into the insulator, the surface is slightly negatively-charged since a surface dipole lyaer is generated due to the implantation. An rf-plasma-sputter type heavy negative-ion source which delivers milliamperes of negative ions, can support research and applications of negative-ion implantation.
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