Characterization of extrusion formation during high temperature anneal

Stress relaxation in aluminum-copper (Al-Cu) films at elevated temperatures can result in problematic extrusion formation. Extrusions in Al-Cu lines can potentially grow towards neighboring lines and short devices, resulting in reliability and product yield concerns. Improved understanding of the driving mechanisms behind extrusion formation is necessary to quantify the contribution of different variables for better process window control. Scanning electron microscopy was used to view the extrusions that form along the sides of metal lines before oxide deposition. A kinetics study was performed on various metal stacks and metal line dimensions in addition to a comparison study of standard anneal and rapid thermal anneal processes. The results of these studies were analyzed and compared with a model assuming diffusion based growth as well as with a finite element model.