Au⁻Au surface activated bonding is promising for room-temperature bonding. The use of Ar plasma vs. O₂ 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 O₂ 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/m²), while that of samples obtained using O₂ plasma treatment was low (surface energy: 0.1⁻0.2 J/m²). X-ray photoelectron spectroscopy analysis revealed that a gold oxide (Au₂O₃) layer readily formed with O₂ plasma treatment, and this layer impeded Au⁻Au bonding. Thermal desorption spectroscopy analysis revealed that Au₂O₃ thermally desorbed around 110 °C. Annealing of O₂ plasma-treated samples up to 150 °C before bonding increased the bonding strength from 0.1 to 2.5 J/m² due to Au₂O₃ decomposition.
Keywords: Ar plasma treatment; Au–Au bonding; O2 plasma treatment; heterogeneous integration; low-temperature bonding; ultrathin Au films; wafer bonding.