Aluminum alloys, such as Al-Cu and Al-Cu-Si are the most extensively used metals for interconnects in integrated circuit. The beneficial effect of the Cu addition is to increase the resistance to electromigration and hillock growth. Si is also often added to minimize the erosion in contact windows and enhance the metal corrosion resistance in the wet photoresist development process. Due to the importance of grain boundary transport in electromigration failure, factors such as grain size and grain size distribution, have an important influence on the failure threshold in conjunction with the level of Cu. In addition, the level of Cu and Si has many detrimental effects, such as microcorrosion caused by the galvanic action of Al2Cu precipitates and the occurrence of Si precipitates, which result in points of high resistance. It is not clear what deposition conditions and what quantities of Cu and Si would lead to the optimum properties, in relation to the grain size and the size and distribution of Al2Cu and Si precipitates. Reductions of Cu and Si content can help to decrease the formation of Al2Cu and Si precipitates, but it is believed that these precipitates are readily formed due to the large surface to volume ratio. In the present study, the specific correlations between processing conditions, the amount of Cu and Si additions, and the microstructure of the Al alloy thin film are evaluated for the development of an improved alloy system.