MICROSTRUCTURE STUDIES OF Al-Cu SUBMICRON INTERCONNECTION.

Abstract

It has been recognized that there is a strong correlation between microstructure and electromigration resistance in thin film interconnection. This is particularly true when the linewidth reduces to the submicron range, where the grain size is comparable to the width. The microstructure of fine metal lines in the submicron range are studied. Microstructure studies on the Al-Cu fine lines were carried out by transmission electron microscopy (TEM). The authors report the result of grain morphology and grain size on these fine lines, and the effects of linewidth and annealing on grain growth and their electromigration characteristics. In the annealed submicron lines, grain boundaries near the free surface tended to lie perpendicular to the specimen surface, and the columnar grain structure was enhanced. The grain structure was found to resemble bamboo in the 0. 5 mu m line. Grain growth was nearly ideal when the grain size was below the film thickness, but it slowed down very rapidly when the grain size approached the film thickness. The final grain structure and ultimate grain size are believed to be determined by both the film thickness and the linewidth in the submicron range.