Reliability aspects of stress-induced voiding in 0.25 /spl mu/m metallization

Abstract

Stress Void formation of Al based interconnects (0.25 /spl mu/m ground rule) due to high density plasma (HDP) oxide deposition process has been reported in the literature very recently. The voids are caused by the thermal expansion mismatch between Al and oxide. It is proposed that the voiding is accelerated by the TiAl/sub 3/ formation. In this paper, void formation is investigated for differently processed metal lines. Measurements include stress-migration (SM) as well as electromigration (EM) reliability tests on two types of test structures. The aim of the work was to study the influence of the stress voids on the EM performance. From reliability investigations presented in this paper it can be concluded that pre-existing voids in metal lines result only in a small decrease of electromigration median time to failure (MTF). However a decrease of the current density exponent n is found. This leads to a reduction in life time.