Stress-induced void formation in metallization for integrated circuits

The term “stress migration” in Al lines in ICs is used in a broad sense to described thermally induced void formation and resulting failures, i.e. open circuits and increases in resistance, which occur in high-temperature processes, such as insulating film deposition on Al lines in IC fabrication, and during storage tests at elevated temperatures for evaluating the reliability of fabricated ICs. Stress migration degrades the IC production yield and reliability. The problem becomes more serious as the linewidth decreases. This paper reviews stress migration-induced void formation and resulting failures in Al lines, and is intended to clarify current experimental and theoretical knowledge of their characteristics. The main topics discussed are classification and characteristics of stress migration, accelerated life test results and failure prediction, Al line stress, void formation models and countermeasures for reducing failures.