RELIABILITY SIMULATION OF AC HOT-CARRIER DEGRADATION FOR DEEP-SUBMICRON MOSFETS

High performance under low supply voltage is required for ULSIs in com bination with the higher packing density that results from scaling dow n to the deep sub-micron region. For this requirement, the conventiona l method, using the DC hot carrier lifetime of MOSFETs as measured by DC stress, overestimates the degradation caused by real circuit operat ion. As a result, the improvement of MOSFET performance is limited by attempting to satisfy the overestimated hot carrier criteria under DC stress. Therefore, it is strongly desired that the reliability simulat ion estimate accurately hot carrier degradation in real circuit operat ion. We have found that the degradation rate depends on the stress con ditions and can be expressed in terms of the difference between the ga te and drain voltages. Hence, in this paper, we propose a new method o f modeling and calculation of hot carrier degradation that incorporate s this dependence and will demonstrate improved accuracy in predicting degradation and life time for both AC and DC bias conditions. We also propose a new duty ratio extraction method that can be used to predic t the lifetime for hot carrier degradation under actual circuit operat ion.