Aging and baking effects on the radiation hardness of MOS capacitors

A decrease in the oxide-charge trapping efficiency of Al- and TaSi-Al-gate MOS capacitors with oxide thicknesses ranging from 33 to 100 nm was observed after more than 14 years of room-temperature storage. The decrease in trapping efficiency can be reduced or even eliminated in Al-gate (and to a lesser degree TaSi-Al) devices by baking them at temperatures up to similar to200 degreesC. This change in aged-device radiation response after baking is largely independent of baking time, at least for 1-18 h bakes. Poly-Si gate capacitors processed and stored under similar conditions show no significant change in radiation hardness due to aging or baking. Mechanisms responsible for this behavior and implications of the results for hardness assurance are discussed.