Effective high temperature circuit testing
In many industrial applications safety and efficiency electronic systems are made up from miniaturised, integrated logic and memory circuits. To ensure safety and reliability, these circuits must operate properly even when exposed to temperatures as high as 200°C. In the automotive, aerospace, avionics, ship and oil extraction industries, working environments with even higher temperatures are present and circuit failure modes have to be seriously considered. The ATHIS project has developed highly efficient testing strategies capable of identifying defective circuits. Very large-scale integrated (VLSI) circuits are being continuously minimised. Consequently, thin film conductors and interconnects are subject to higher current densities. In combination with a high temperature environment the most important failure mode that manifests itself is electromigration. Momentum transfer between conducting electrons and the ions that make up the lattice of the substrate material simply result in the actual transport of material and the inevitable breakdown of the circuit involved. Electromigration is not the only high temperature failure mode. Time dependent dielectric breakdown and hot-electron effects must also be considered. Highly energetic electrons, hot electrons, capable of tunnelling through the thin oxide gate, show up as gate current, and cause circuit failure. Time Dependent Dielectric Breakdown, or TDDB, is one of the most heavily researched failure mechanisms in the semiconductor reliability community. Since the 1960s, researchers have struggled to understand the nature of how an oxide degrades over time. Nevertheless both physical phenomena, TDDB and hot electron effects, depend very little on temperature and the main failure mechanism remains electromigration. Since electromigration manifests itself as either a short or an open circuit, current and voltage test methods suffice for failure detection. Project partners have developed sophisticated fault models to be used by design automation tools for the creation of accurate test patterns. The ATHIS project has therefore considerably contributed to enhancing high temperature circuit reliability.
