Study of Cu diffusion in an Al-1 wt%Si-0.5 wt%Cu bond pad with an Al-1 wt%Si bond wire attached using scanning electron microscopy

Abstract

A study with scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) of the Al-l wt.%Si-0.5 wt.%Cu bond pad metallisation with Al-l wt.%Si wires bonded to it revealed Cu diffusion from the bond pad into the Al wire after an annealing process. investigation at different annealing times showed a Cu depletion zone which indicates that the radius R is consistent with a root t behaviour. The diffusion velocity, as determined experimentally, is close to the velocity of grain boundary diffusion. This observation has important consequences with respect to electromigration testing of Ai(Si)Cu metallisations bonded with Al wires. The electromigration (EM) process can be influenced by a bad placement of the Al bond wire with regard to the test lines. If bonded too close to the test line, Cu diffusion out of the test line is possible during annealing, thereby changing the microstructure locally and thus the EM process. (C) 1998 Elsevier Science Ltd. All rights reserved.