Electromigration in fine-line sputter-gun Al

The electromigration behavior of Al films, deposited by the sputter gun (varian s-gun) and ranging in alloy content from 0.5% Cu to 2% Si has been evaluated for 2.5 cm long, 1–4 μm wide conducting stripes. An inverse square dependence of lifetime on current density has been verified. Furthermore, it has been shown that film composition affects the electromigration lifetime through its contribution to the grain structure, in that, an increase in lifetime accompanies an increase in grain size and a decrease in spread of the grain size distribution. Increasing the Si content is detrimental, since it results in a reduction in grain size. Failures occur by the random growth of subsurface voids along the conductor length. The s-gun films have a completely random orientation in contrast to electron beam evaporated Al-0.5% Cu, which exhibits a prominent 〈111〉 fiber texture. This preferred grain orientation in the case of the latter is held responsible for its superior lifetime in comparison to the sputtered films.