Product failures: Power-law or exponential voltage dependence?

The product failures voltage acceleration has traditionally been modelled with exponential voltage dependence. However with voltage scaling, the voltage acceleration parameter (VAP) in an exponential model has increased as V⁻¹ - as expected for dielectric breakdown in either back-end or front-end. This suggests an exponential model is probably quite conservative and a power-law model may be more appropriate for 90nm and beyond. Even if an exponential model continues to be used, this understanding can help assess the amount of conservatism built in such a model.

Introduction

Voltage scaling has played a pivotal role in enabling semiconductor products to be offered with increasing levels of functionality while maintaining cost, power and performance constraints. At the same time, new product definition and design cycles ranging from six months to two years mandate a requirement to provide realistic projections of product reliability as a function of target operating conditions. This paper shares some experience in this arena, identifying some critical mechanisms that affect product reliability and how to realistically project product reliability from proper interpretation of early life failure rate (ELFR) and high temp operating lifetest (HTOL) voltage stress data.