NEW METHOD FOR ASSESSING DIELECTRIC INTEGRITY OF MOS OXIDES

Abstract

Evaluation of dielectric integrity of MOS oxides is essential because the performance, especially relative long term performance of modern MOS integrated circuits depends upon the functional stability of thin oxides. Since mechanisms of high field degradation are not yet clear, critical assessment of dielectric qualities of oxides based on microscopic models of wearout can not be done. However experimental observations, such as positive charge generation with high field stressing are common. Also microscopic defects generation because of high field stressing seems to be the cause of degradation. We have shown that defect generation shows same behavior over a large range of stress conditions. Our experiments show that there is a monotonic flat band voltage shift with stressing because of this. This flatband shift acts as a signature of wearout. On the basis of these observations a new method is suggested for assessing dielectric reliability and has the advantage of being close to the physical mechanisms of high field degradation of oxides.