Nitrided gate oxides for 3.3-V logic application: Reliability and device design considerations

Device characteristics and reliability in a 3.3-V logic CMOS technology with various gate oxidation and nitridation processes are described. The technology was designed to extend 3.3-V devices to the ultimate dielectric reliability limit while maintaining strict manufacturing cost control. A nitrided gate oxide provided the means to maintain hot-electron reliability at the level of the previous iteration, but at higher performance and lower processing cost. Conventional furnace processes in nitrous and nitric oxide, high-pressure oxidation in oxygen and nitrous oxide, and rapid-thermal processes using nitrous and nitric oxide were investigated. We found that the concomitant variations in fixed charge and thermal budget have a significant influence on both n-FET and p-FET device parameters such as threshold voltage, carrier mobility, and inverse short-channel effect (ISCE). Reliability effects, such as charge to breakdown (QBD), hot-electron degradation,and negative-bias temperature instability (NBTI) were examined and correlated with the nitrogen profile in the gate dielectric. Secondary ion mass spectroscopy (SIMS) profiles were used to characterize the oxidation techniques and to correlate gate dielectric composition to the parametric and reliability parameters.