The effects of deposition and annealing condition on the microstractural evolution of Al-Cu and Al-Cu-Si thin films

Aluminum alloys (Al-Cu and Al-Cu-Si) are the most extensively used metals for interconnects in integrated circuits. Cu additions enhance electro-thermal migration resistance, but may increase corrosion susceptibility in both reactive ion etching and wet processing due to the formation of Al2Cu (θ) precipitates. Si was originally added to minimize erosion in contact windows, however it was recently found that the addition of 1.5% or 0.5% Si in Al-Cu alloy improves its corrosion resistance. θ precipitates in binary alloys have been found to occur at the Al/sublayer interface during high temperature (>200°C) deposition due to the fast surface diffusion of Cu. For the higher temperature deposition in the Al solid solution region, platelike θ precipitates were also formed at the interface and grain boundaries during a fast cooldown of wafers. However, it has not been well understood how the addition of Si in Al-Cu alters the thin film microstructure and increases the corrosion resistance. In this work, the effects of Si addition and deposition temperature on the film microstructure were studied for different alloy compositions and sublayers. The effects of thermal annealing on the interaction of Al films with Ti-W sublayer were also studied.