MOS Hardness Characterization and Its Dependence upon Some Process and Measurement Variables

The effects of oxidation time (or oxide thickness) on the hardness of 1000°C dry oxides on silicon is shown to result in a post-irradiation flatband voltage shift (¿VFB) that is proportional to oxide thickness squared (dox2) for high energy irradiation and ¿VFB ¿ dox for vacuum ultraviolet (VUV) radiation and negative corona charging. This is in disagreement with previously reported work in which ¿VFB ¿ dox3 was measured for high energy irradiation. The present experiments strongly suggest that hole traps are located mainly at the Si-SiO2 interface and have a total area density that is independent of oxidation time or oxide thickness at a constant oxidation temperature. Trace amounts of water were added to the oxidation ambient of a modified hard-oxide furnace tube in levels ranging from 16 parts per million (ppm) to 50,000 ppm. The results of these experiments show that trace levels of water do not significantly degrade the radiation hardness of dry oxides.