The Effect of Entrapped Krypton 85 Gas on Device Reliability

The effect of entrapped Kr85 radioactive gas upon the threshold voltage and junction leakage of MOS transistors is quantified through device modeling and accelerated testing. The interactions of transistor channel length, channel width, oxide thickness, radiation level, and exposure time are experimentally determined. A mathematical model is developed which predicts threshold voltage shifts as a function of these processing variables and the amount of entrapped Kr85 gas. This model is used to establish, from a reliability standpoint, acceptable levels of entrapped Kr85 for current and new generation devices.