Correlation of electromigration defects in small damascene Cu interconnects with their microstructure

Limited reliability of interconnect material mainly due to current induced electromigration defects is one of the serious issues of actual and future microelectronic devices. The influence of interfaces and microstructure on electromigration damage in Cu interconnects became an open question again and needs further studies. In order to find correlations between microstructural details and localization of electromigration defects generated in narrow electroplated Cu lines, microstructure of entire line was recorded by electron back scatter diffraction measurements with high lateral resolution, and then electromigration test was performed in high vacuum under direct SEM observation. In the result, a number of hillocks were found to have grown in the vicinity of (1 0 0) grains having at least one high angle grain boundary around it. Fatal voids often formed at the cathode end and produced dielectric cracking in some cases. Furthermore, voiding started from the sidewall of interconnect trenches mostly at such places where (1 1 1) grains with high angle grain boundaries were located.