Three-dimensional imaging of nanovoids in copper interconnects using incoherent bright field tomography

As integrated circuits have shrunk, conventional electron microscopies have proven inadequate for imaging complicated interconnect structures due to the overlap of features in projection. These techniques produce transmission functions with a nonmonotonic dependence of intensity on thickness for common microelectronic materials, making them unsuitable for tomography. We report the use of an incoherent bright field imaging technique in a scanning transmission electron microscope optimized for the three-dimensional reconstruction of thick copper microelectronic structures. Predictable behavior of the signal in samples up to similar to 1 mu m thick allows us to reconstruct and quantify the shape and volume of stress voids within Ta-lined interconnects.