The effects of the grain size in the Al layer and the passivation structure on the electromigration performance in the two level Al interconnections, the bottom (M1) and the top (M2) interconnections, each of which had a TiW/Al/TiW multilayered structure, were studied regarding void and extrusion formation in the Al layers. In M2, the resistance increase of the interconnection having a larger grain size in the Al layer formed with a reflow treatment, was smaller than that without any reflow treatment. Larger numbers of Al extrusions were, however, observed in the M2 interconnection with the reflow treatment than without it. In M1 which was buried under a thick insulation layer, enlargement of the Al grains by the reflow treatment was more effective to suppress the resistance increase than in the M2 interconnections. This result meant that the combination effect occurred when both treatments, enlargement of the Al grains in the interconnection and strengthening the passivation layer surrounding it, were applied simultaneously.