In situ local measurement of sub-threshold strains generated during the electromigration of a 0.3-μm-wide Al interconnect was performed for the first time using convergent-beam electron diffraction (CBED) in a transmission electron microscope (TEM). Thermal strains were also analyzed and provided verification for the electromigration analysis. Spatially averaged strains resulting from thermal cycling and electromigration quantitatively agree with models and data from previous studies. However, the local strains exhibited variations as large as 2 × 10−3. After eliminating other possible mechanisms, the strain inhomogeneity is attributed to local plasticity through source-limited dislocation activity.

Electromigration-induced hillock growth in polycrystalline Al segments was extensively investigated. Hillocks composed of columnar grains grew near the anode by epitaxial Al addition at the interface between the Al and underlying TiN layer, which pushed up the original Al film. The hillocks rotated away from their initial (111) out-of-plane orientation in a manner consistent with the physical rotation of the hillock surface. Wedgelike and rounded hillocks were observed, and their formation is explained by the interaction between grain extrusion and grain growth. Trends elucidated by review of both thermal- and electromigration-induced hillock studies can be explained by the mechanisms identified in this work.

Copper thin films were deposited by sputtering, electron beam evaporation, and electroless plating onto nitride membranes for TEM analysis. The samples were heat treated in-situ from room temperature to 600 °C for structural and chemical analysis. The as-deposited and heat treated microstructures were investigated. Orientation changes with heat treatment and reactions among the sample layers were analyzed by electron diffraction. This work provides baseline information for a study of the thermal evolution of copper lines.