Effect of postoxidation annealing on the reliability of rapid thermal thin gate oxides

The reliability of thin gate oxides grown by rapid thermal oxidation in O/sub 2/ followed by one and two step postoxidation annealing (POA) in N/sub 2/ was studied. The one step POA was carried out by switching O/sub 2/ into N/sub 2/ immediately after oxidation without changing temperature, while the two step POA was cooled down first and subsequently heated to the same temperature as oxidation in N/sub 2/. It was experimentally observed that the oxide thickness increases significantly with the POA time in one step POA, while the oxide thickness shows very little change during two step POA. The interfacial properties and the oxide breakdown endurance can be improved by the two step POA. Also, the radiation hardness of oxide is less degraded by the two step POA than by one step POA. The effect of oxide thickness variation due to POA is chiefly responsible for the observation and is important to thin gate oxides.