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 does not control stress time, and it is difficult to 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 thermally grown SiO2, 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-degrees-C and above for 1 h in H-2 caused the breakdown strength of the oxide to be sharply reduced due to a metallurgical reaction between Al and SiO2.