Low temperature bonding of wafers coated with low-kappa dielectric film of carbon-doped oxide (CDO) is demonstrated. Direct bonding is successfully achieved by using oxygen plasma activation which modifies the low-kappa CDO surface to be more hydrophilic. It is discovered that after a 300 degrees C anneal in N(2) ambient for 3 h, bond strength of the bonded wafer pair is enhanced by 33.8% from 1270 to 1700 mJ/m(2) with oxygen plasma surface activation. This enhancement is attributed to reduction in carbon content at the bonding surface that increases the surface energy. Void growth is observed with post-bonding isothermal annealing and it can be suppressed with multistep annealing. Wafer bonding with low-kappa dielectric is a promising choice to realize high density 3D IC for performance enhancement in future integrated circuits and systems. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.005111jes] All rights reserved.