The evolution of barrier properties during reliability testing of Cu interconnects

The investigation of stress-induced voiding (SIV) is one of the key aspects to characterize metallization reliability. Typical test methodologies include the investigation of resistance shifts during temperature storage tests at temperatures between 150°C to 275°C. During these tests, only very small resistance increases dependent on the test structure are allowed. Physical failure analysis of such samples typically reveals voids below the vias of the test structures. However, recently we encountered unusual resistance shifts at the highest stress temperature which did not yield classical stress-induced voiding detectable by failure analysis. We found changes in barrier integrity explaining the resistance shift by barrier oxidization. This has been verified by specially prepared material as well as extensive failure analysis investigation. © 2009 American Institute of Physics.