Modification of charge produced during plasma exposure in aluminum oxide by vacuum ultraviolet radiation

A temporary increase in the conductivity of aluminum oxide sputter deposited on the surface of aluminum wafers was made by exposure to VUV (vacuum ultraviolet) radiation produced by a synchrotron light source. The oxide was charged, either positively or negatively, by exposure to a nonreactive inductively coupled plasma, under typical plasma processing conditions. We show the dependence of the conductivity on the energy of the incoming radiation, and conclude that only those photons whose energy is above the oxide bandgap are capable of producing a temporary increase in conductivity. By appropriately exposing localized regions of pre-charged oxide samples to the vacuum ultraviolet radiation, we produce regions of charge depletion or enhancement in and around the exposed areas as a result of two competing processes: photoemission and enhanced conductivity. We conclude that VUV radiation may be used to significantly decrease plasma-induced surface charging of dielectrics.