Cu passivation for enhanced low temperature (≤300 °C) bonding in 3D integration

Self-assembled monolayer (SAM) of alkane-thiol is applied to provide temporary passivation on Cu surface for protection against oxidation. The SAM is less susceptible to partial desorption when the samples are stored at low temperature and in inert ambient. Surface analysis shows that SAM is effective in retarding surface oxidation and the degree of protection is higher for SAM with longer chain length. Thiol-based SAM also shows better oxidation protection compared to Benzotriazole (BTA) and is readily desorbed away via thermal annealing. Wafer-to-wafer bonding result shows shear strength enhancement in the Cu-Cu bond when the appropriate chain length of SAM is used. Although the longer chain SAM may have provided better protection to the Cu, it is harder to remove by thermal desorption and therefore its overall benefit is minimal. (C) 2013 Elsevier B.V. All rights reserved.