Continued miniaturization of conductor geometry below 0.5μm has by a concomitant decrease in Al deposition temperature, typically below 300°C. The degree of reliability exhibited by these films is strongly dependent on the grain size distribution and metallurgical configuration. This investigation focuses on the impact of post-deposition processing on changes in conductor microstructure and electromigration for films deposited at low temperature. AlCu(l%)Si(l%) was deposited at 300°C on PECVD phosphosilicate glass. The impact of post-deposition thermal budget on the as deposited grain size and distribution, preferred orientation and stress/strain states were analyzed using scanning electron microscopy, X-Ray diffraction and bending beam technique, respectively. These characteristics were also measured on unpassivated films subjected to the same thermal budget as SiO2 passivated films so that the geometric confinement and Al-SiO2 surface interaction could be quantified. Electromigration characteristics were measured for linewidths in the range W=1.0μm to W=10μm, for passivated and unpassivated films. A direct correlation between passivation and grain size was observed for both failure modes. This paper will also discuss the relationship between film stress and preferred orientation, the observed failure modes and their linewidth dependence.