Fundamental factors governing improved performance of Al–Si/Ti multilayer metallization for very large scale integration

Abstract

Fundamental factors governing the previously observed improvements in conductivity, hillock growth resistance, and thermal stability of the Al–Si/Ti multilayer metallization system have been investigated using various bulk characterization methods and surface analytical techniques (Auger electron spectroscopy and x-ray photoelectron spectroscopy). Si partitioning from the Al–Si into Ti layer duirng annealing at 450 °C was found to be associated with the formation of a ternary phase similar to TiAl3, but enriched in silicon. In the Al–Si/Ti–Si multilayer metallization system, Si migrates into the Al–Si layer and Al migrates into the Ti–Si layer during annealing. These results suggest that the TiAl3(–Si) phase is thermodynamically more stable than the TiSi2 and TiAl3 phases and that its formation is not kinetically limited by diffusion of Si and Al in either Al or Ti at 450 °C. Formation of TiAl3(–Si) between Al layers is an important factor contributing to improved conductivity of the Al–Si/Ti layered metallization. Formation of interspersed hard layers of TiAl3 or TiAl3(–Si) phases, as well as precipitation of these phases within the Al or the Al–Si layers, appears to be responsible for the improved hillock growth resistance of these multilayered structures.