A self-assembled monolayer (SAM) of 1-hexanethiol is formed on a copper (Cu) thin layer coated on silicon (Si) wafers with the aim to protect the surface against contamination during storage in room ambient. After 3 days of storage, the SAM is desorbed with an in situ annealing step in inert N-2 ambient to provide a clean Cu surface and a pair of wafers is bonded at 250 degrees C. It is observed with scanning acoustic microscopy that there is a clear reduction in the interfacial void density in the bonded pair compared with the control sample without SAM passivation. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3487926] All rights reserved.