Scanning probe microscopy generated out-of-plane deformation maps exhibiting heterogeneous nanoscale deformation resulting from thermal cycling of Cu–polyimide damascene interconnects

Room-temperature scanning probe microscopy was used to generate out-of-plane deformation maps around Cu vias and polyimide mesas in single-level Cu–polyimide damascene interconnect structures subjected to a room-temperature to 350 °C thermal cycle. The deformation maps are obtained by taking the difference between the images obtained before and after thermal processing. The deformation of the Cu is shown to be highly heterogeneous on the submicrometer scale. Direct evidence of Cu–Ta interfacial sliding, Cu–Cu grain boundary sliding, and diffusion creep is presented. The direction of Cu–Ta sliding is shown to depend on polyimide mesa size. A hot-stage atomic force microscope was used to show that hillock/extrusion growth occurs at temperatures between 130 and 180 °C. We propose that this hillock/extrusion growth is correlated with dips in stress–temperature plots for blanket, uncapped Cu films in the same temperature range and that the absence of dips for nitride-capped Cu films is due to suppression of the hillock/extrusion growth.