Determination of transistor infant failure probability in InGaP/GaAs heterojunction bipolar technology

A novel circuit for measuring the infant mortality rate in InGaP/GaAs HBT Technology is presented. The circuit allows reliability stressing to be performed on as many as 100,000 transistors per wafer and is necessary in order to predict the infant circuit failure rate in circuits with >500 transistors without costly burn-in screens. This new circuit allows for the rapid identification of failed transistors and subsequent failure analysis to allow for process improvements. A variation of the same circuit has also been used to estimate the activation energy, Ea, of the infant failure mechanism. Rough estimates of Ea indicate that the infant failure mechanism is ∼0.5 eV, and that there may be two distinct failure mechanisms responsible for infant failures. Process defects have not been found on the vast majority of failed transistors, and there is good correlation between the substrate dislocation density and the infant failure rate. We have concluded that substrate dislocations are the leading cause of infant mortality in our HBT process.