Processing Effects on Steam Oxide Hardness

It is well known that processing steps strongly affect the radiation tolerance of MOS oxides. In this paper we present the effects of post oxidation anneal on the radiation hardness of steam grown oxides. Radiation hardness varies systematically with anneal time and temperature and can be controlled over a more than order of magnitude range. For each anneal temperature there is an optimum anneal time which gives the best radiation hardness. Extending the anneal time beyond the optimum tends to degrade the hardness with the square root of time. A model involving the diffusion of excess silicon into the oxide is proposed to explain the hardness degradation for extended anneals. Additional data presented show a square law dependence of radiation induced flatband shifts on oxide thickness, and the effects of low temperature hydrogen treatments and aluminum sinter steps on radiation performance.