Comparison of Argon and Oxygen Plasma Treatments for Ambient Room-Temperature Wafer-Scale Au-Au Bonding Using Ultrathin Au Films

Au-Au surface activated bonding is promising for room-temperature bonding. The use of Ar plasma vs. O-2 plasma for pretreatment was investigated for room-temperature wafer-scale Au-Au bonding using ultrathin Au films (<50 nm) in ambient air. The main difference between Ar plasma and O-2 plasma is their surface activation mechanism: physical etching and chemical reaction, respectively. Destructive razor blade testing revealed that the bonding strength of samples obtained using Ar plasma treatment was higher than the strength of bulk Si (surface energy of bulk Si: 2.5 J/m(2)), while that of samples obtained using O-2 plasma treatment was low (surface energy: 0.1-0.2 J/m(2)). X-ray photoelectron spectroscopy analysis revealed that a gold oxide (Au2O3) layer readily formed with O-2 plasma treatment, and this layer impeded Au-Au bonding. Thermal desorption spectroscopy analysis revealed that Au2O3 thermally desorbed around 110 degrees C. Annealing of O-2 plasma-treated samples up to 150 degrees C before bonding increased the bonding strength from 0.1 to 2.5 J/m(2) due to Au2O3 decomposition.