DIFFUSION OF COPPER THROUGH DIELECTRIC FILMS UNDER BIAS TEMPERATURE STRESS

Copper diffusion in various dielectric films as a function of electric field and temperature is reported. In this study, we characterized th e leakage current through various dielectric films as a function of el ectrical field and elevated temperature. Both electric field and tempe rature are observed to affect strongly the dielectric barrier lifetime . Nitride and oxynitride films are found to be much better barriers th an thermal oxide while plasma TEOS had a much lower barrier lifetime. The activation energy of copper diffusion in thermal oxide is determin ed to be 1.2 eV. A three-step model is proposed to explain the observe d current-time characteristics. In the first stage, the applied bias c auses the injection of positively charged copper ions into the dielect ric. The lack of a neutralizing electron current results in space-char ge build up which sets up an opposing field and reduces the ionic curr ent. The second stage represents primarily the thermal diffusion of co pper ions and neutral atoms. Finally, in the third stage, enhanced ele ctric fields in the dielectric lead to breakdown.