Effects of insulator surface roughness on the overlying aluminum alloy film properties and electromigration performance in Al alloy/Ti insulator layered interconnects have been investigated. Insulator surface roughness changes the roughness and crystallographic orientation of Al/Ti layered films formed on the insulator. In particular, the effect is prominent in the case of high‐temperature sputtering of Al alloy films. A rough insulator surface deteriorates the roughness and crystallographic orientation of the Al alloy film formed on the insulator, while a smooth insulator surface improves those properties. The insulator surface roughness does not change the roughness and crystallographic orientation of the Al alloy film without a Ti underlayer. Ti roughness and crystallographic orientation are improved on a very smooth surface insulator resulting in improvement in the roughness and crystallographic orientation of the Al alloy film formed on the Ti layer. As a result, the electromigration performance in Al/Ti layered interconnects changes according to the underlayer insulator surface roughness.