AVS 46th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoM

Paper PS-MoM3
Direct Experimental Determination and Modeling of VUV induced Dielectric Conduction during Plasma Processing

Monday, October 25, 1999, 9:00 am, Room 609

Session: Plasma Damage
Presenter: M.V. Joshi, Stanford University
Authors: M.V. Joshi, Stanford University
J.P. McVittie, Stanford University
K.C. Saraswat, Stanford University
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The processing plasma provides a source of high intensity VUV (vacuum ultra-violet) light which is incident on IC dielectrics. It also sets up considerable electric fields across these dielectrics due to either non-uniformity or electron shading induced plasma charging. This is expected to cause photo-current flow in these dielectrics. These photo-currents can damage the underlying devices through a variety of mechanisms and change the charging profiles due to electron shading during plasma processing. Thus determination of the relationships between incident photon density, photon wavelength, applied electric field and photo-current density is vital not only to understanding and controlling photo-current damage to devices during plasma processing but also to accurately model electron shading damage mechanisms. In this work we study the photo-currents that flow through the bulk of the dielectrics as opposed to those flowing on the surface. Bulk photo-conduction would explain the damage seen during dielectric depostion in a plasma chamber. We use a high density plasma as the source of VUV light and a independent very low density plasma separate by a thin filter/window to provide the electric fields and also to act as the current source for the VUV induced photo-currents. This allows independent variation of UV intensity and plasma charging electric fields. The probe consists of a bare polysilicon pad and a nearby similar pad covered with the dielectric. These pads are biased using a voltage source and current drawn through them is measured allowing the determination of the current density - electric field characteristic for the given dielectric independent of the biasing plasma. We measured photo-current density versus applied electric field, dielectric thicknesses, dielectric types, incident photon density, incident photon wavelength, transient effects and in dual dielectrics. We propose a model to explain these effects based on hole trapping and electric field dependent hole-electron recomibination cross-section in the dielectric. This model allows prediction of VUV photo-conduction damage in realistic semiconductor processing structures.