Microstructural effect on the electromigration of aluminum interconnects

Abstract

Summary form only given. A new technique for studying aluminum microstructure is introduced. It utilizes reactive ion etching (RIE) to delineate the Al grain structure so that it can be clearly seen using a scanning electron microscope (SEM). The RIE/SEM technique produces identical results of the average Al grain radius and the grain size distribution as those obtained using transmission electron microscopy (TEM). The advantage of this technique over TEM is that sample preparation is greatly simplified and a large contiguous area can be studied. Previous studies of the Al microstructure, using TEM, have shown that there is a drastic increase in the electromigration median-time-to-fail (MTTF) as the Al grain diameter approaches the metal line width. The phenomenon is known as the bamboo effect. The authors present Al microstructure data from electromigration lines using RIE/SEM technique to show an additional cause for the increase in MTTF hidden in the bamboo effect. The total number of grains, triple points, bamboo grains, and electromigration MTTF were measured from Al-1%Si metal electromigration lots. The results show that the number of triple points is a more critical factor in electromigration performance than the number of bamboo grains. >