Dielectric Breakdown Strength of SiO2 Using a Stepped-Field Method

The ramped-field technique has been widely used for determining dielectric breakdown in thin insulating films. But this method oes not control stress time, and it is difficult o define an irreversibly broken down capacitor based solely on observations of current during stressing. A more advanced stepped-field method is described, which provides well-defined stress times and guarantees catastrophic breakdown in all cases. MOS capacitors, formed by depositing Al dots on ther-mally grown SiOz, were used to determine oxide breakdown. The breakdown field was found to decrease logarithmically with the stressing time. A model is presented which relates the probability of breakdown to the stressing field strength and stressing time. Dielectric breakdown strength was also investigated as a function of annealing time and temperature. Annealing at 500 ~ and above for 1 h in H2 caused the breakdown strength of the oxide to be sharply reduced ue to a metallurgical reaction between A1 and SiO2. Traditionally, dielectric breakdown strength as been measured by applying a steadily increasing voltage across a thin insulating film, and measuring the leakage current. A sudden, large increase in current is assumed to indicate dielectric breakdown, at which point the electric field i