Effects of Varying Annealing Temperatures on the Microstructure and Electromigration Performance of Copper Interconnects

Abstract

In the semiconductor industry, the ongoing demand for the miniaturization of electronic devices has significantly increased the number of components integrated into a single wafer. Consequently, the dimensions of interconnects in integrated circuits (ICs) must be minimized to connect more transistors. This trend inevitably leads to a substantial rise in current density within the interconnects, posing a major reliability challenge known as electromigration (EM). EM can result in further reliability issues, ultimately causing device failure. Extensive research has been conducted over the past decades to mitigate the impact of EM.
This study focuses on copper (Cu) interconnects, investigating the effect of annealing on their microstructure and the resulting impact on resistivity, with particular emphasis on how the microstructure influences EM. Additionally, the progress of attempting to forming Cu nanotwins via electroplating to resist EM is briefly investigated. Sputtered Cu was annealed at temperatures of 300℃, 400℃, 500℃, and 700℃, and the resulting microstructural variations were characterized by using EBSD. The findings reveal a progressive strengthening of the (111) texture in Cu film and an increase in grain size with higher annealing temperatures. Additionally, a notable decrease in grain boundary length was observed as the annealing temperature increased, correlating with reduced resistivity across the annealed samples. Moreover, the study highlights a elimination of defects and strain within the Cu films with increasing annealing temperatures.
Furthermore, EM measurements were conducted using accelerated tests under conditions of high current stress and high temperature. The variations in the microstructure of Cu films were described, and the correlation between EM mechanisms and microstructural parameters was discussed. To quantify the progress of EM, the drift velocity for each sample was calculated, revealing a trend of slower drift velocities with increasing annealing temperatures. This work provides a unique opportunity to investigate the impact of annealing on the microstructure of Cu interconnects and to study how these changes influence EM performance. The findings contribute to a deeper understanding of EM and enhanced reliability prediction in electronic devices.

Keywords: electromigration, copper interconnects, microstructure, annealing.