Characterization and impact of reduced copper plating overburden on 45 nm interconnect performances

During first metal level interconnects fabrication, a controlled modification of the electro-deposited copper over-deposition (overburden) is performed using a partial chemical-mechanical polishing (CMP) step. Next, copper microstructure is stabilized with a short duration hot-plate anneal. Overburden is then removed during CMP end-of-step. Ionic microscopy and EBSD observations of overburden thickness reduction reveal that copper grain growth occurs differently, according to patterned geometries and with a strong texture, as observed in modified films. Reduction of overburden thickness also reveals the capacity of anneal temperature to impact electrical performances. Reliability is impacted for thinnest wires.