A study of the leakage mechanisms of silicided n+/p junctions

Abstract

Leakage mechanisms for shallow, silicided, n⁺/p junctions have been investigated. This study consists of two parts: (a) the isolation of the processing steps that cause junction leakage, and (b) the study of the mechanism for a particular process that causes leakage. Reactive ion etching, improper junction, silicide formation procedures, ion mixing, and mechanical stress are found responsible for junction leakage, although through different mechanisms. Two mechanisms have been identified for junction leakage: (a) generation centers in the depletion region caused by deep levels from damage, or from impurities, and (b) Fowler–Nordheim tunneling caused by irregularities at the silicide/silicon interface at high reverse bias. Junction leakage can be avoided by carefully designing the details of silicide and junction formation and by carefully fine‐tuning the processing steps to prevent damage of the Si substrate after forming the junction. The best junctions are made by implanting As into CoSi₂ and by driving the As into Si from the silicide at 800 °C. The lower temperature drive is possible since all ion damage is contained within the silicide, leaving no damage in the Si substrate to anneal out. Very shallow, silicided, n⁺/p junctions can be fabricated reproducibly. These junctions demonstrate the same electrical characteristics as deeper, nonsilicided junctions, indicating that there is no fundamental barrier prohibiting fabrication of low‐leakage, silicided junctions.