The microstructure and electromigration performance of Damascene-fabricated aluminum interconnects

Novel metal deposition stack and damascene processing methods have been used to fabricate electrically isolated parallel arrays of 1.0 mu m deep aluminum-alloy interconnect trenches varying in width from 0.5 mu m to 16 mu m. The grain size and crystallographic texture of the Al in these trenches has been characterized using transmission electron microscopy (TEM) and local electron backscattered diffraction (EBSD), respectively. Narrow lines (0.5 and 1.0 mu m wide) have a bamboo microstructure, intermediate widths (2.0 mu m wide) are nearly bamboo, and wide lines (4.0 mu m and wider) are polycrystalline. The [111] texture of the lines degrades with decreasing linewidth. A secondary [100] component is demonstrated and its origin proposed. The electromigration reliability of the narrow damascene Al lines was measured, and the observed enhancement of damascene Al interconnects compared to conventionally-fabricated Al interconnects is correlated with the microstructure.