Direct experimental determination and modeling of VUV induced bulk conduction in dielectrics during plasma processing

The processing plasma provides an intense source of vacuum ultraviolet (VUV) photons, which are incident on IC dielectrics. It also induces considerable electric fields across these dielectrics due to either non-uniformity or electron shading induced plasma charging. The combination of these factors can cause photocurrent flow in these dielectrics damaging the underlying devices through a variety of mechanisms. For example damage to underlying devices through interconnects covered with a dielectric has been reported. These photocurrents are also expected to 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 photocurrent density in different dielectrics is vital not only to understanding and controlling photocurrent damage to devices during plasma processing but also to accurately model electron shading damage mechanisms. In this work we measured the VUV induced bulk conduction in dielectrics in CVD silicon nitride and oxide while varying different parameters like dielectric film thickness, VUV intensity, electric field and VUV photo wavelength. We also present some calculations to illustrate the importance of VUV induced bulk conduction in causing device damage