Evaluation of effective stress times and stress levels from mission profiles for semiconductor reliability
Abstract Lifetime and duty cycles of automotive electronics are increasing, inducing new challenges to reliability predictions and testing. For qualification purposes, the automotive industry generates various time-dependent mission profiles with various stressors and varying stress levels according to different use cases. We present a theoretical model, describing the common approach, to reduce the stressors from time-dependent mission profiles to the two single parameters “effective stress level” and “effective stress time” for equivalent reliability testing. In a first step, the cumulative exposure (CE) model is shown to describe the future reliability behaviour after steplike stress level changes. Taking into account the individual characteristic lifetimes T63 of the corresponding Weibull distributions, in a second step, an effective T63 lifetime can be derived. For this calculation, periodic stress cycles are defined and transformed into an equivalent effective stress level. This procedure confirms the industry-wide used approach of dealing with effective stress levels for reliability testing. For the experimental validation metal-oxide-semiconductor (MOS) capacitors are fabricated and stressed by voltage and temperature. The received reliability data fit the theoretical predictions within the statistical variations.