Enhancement of electromigration lifetime of copper lines by eliminating nanoscale grains in highly <111>-oriented nanotwinned structures

• DOI: 10.1016/j.jmrt.2021.11.111
• Publication Date: 2021-11-26T07:20:36Z
• Authors: Dinh-Phuc Tran; Hung-Hsuan Li; I-Hsin Tseng; Chih Chen
• Keywords: Mining engineering. Metallurgy; Transition layer; Oxidation; TN1-997; Nanotwinned Cu lines; 02 engineering and technology; 0210 nano-technology

In this study, we designed and electroplated various regular and nanotwinned copper (nt-Cu) lines. These Cu lines were then covered with a polyimide (PI) layer and heat-treated to some extents prior to electromigration (EM) testing. The results show that the EM lifetime of the nt-Cu lines is approximately 4.7 times longer than that of the regular ones. We found that the EM lifetime has been enhanced by 273% using a heat treatment. The improvement is attributed to the heat-treatment-led elimination of the nt–Cu transition layer (nanoscale grain region). The diffusion paths of Cu atoms at the nt-Cu line bottom were shortened as the number of continuous grain boundaries was decreased under the heat-treatment. Thus, the oxidation and void formation were further suppressed. Additionally, we discovered that the columnar microstructure of the nt-Cu lines remained unchanged under a high annealing temperature. These nt-Cu lines with high thermal stability and EM resistance can be widely used for advanced fine-pitch packaging due to its controlled microstructures.