Quantitative analysis of the mechanical robustness of multilayered bonding pad on a semiconductor device by nanoindentation and nanoscratch tests

Abstract

Mechanical robustness of a bonding pad on an electronic device, consisting of the top aluminum layer, 40 nm thick intermediate titanium nitride (TiN) barrier layer, and 350 nm thick bottom aluminum layer, was investigated with respect to the thickness of top aluminum layer ranging from 250 nm to 650 nm. Mechanical responses of the pad were evaluated using wire pull test, nanoindentation test, and nanoscratch test. The bonding quality was degraded with the decreasing thickness of top aluminum layer, due to the increasing risk of mechanical damage of this layer and the breakage of the underlying TiN layer. The apparent elastic modulus of the thinner pad increased faster than that of the thicker one as a function of indentation depth. Apparent friction coefficient exhibited a complex, yet understandable, pattern amenable to the relative difficulty of the scratch tip traveling through the three layers in the pad assembly. The breakage of TiN caused an abrupt drop in the load vs. penetration curves in the nanoscratch test, the coincidence of which was verified by subsequent cross-sectional analysis. The longitudinal scratch distance to the TiN breakage can serve as a useful parameter to qualify the mechanical stability of the bonding pad. (C) 2013 Elsevier B. V. All rights reserved.