Si-Si wafer direct bonding was performed by surface activation with Ar ion beam bombardment. The X-ray photoelectron spectroscopy (XPS) spectrum of the Si surface before and after the Ar ion beam bombardment was measured in situ to study the bonding condition quantitatively. The condition of the Ar ion beam bombardment gave the effect for the surface roughness, which was measured by Atom force microscope (AFM). The surface roughness is strongly related to the bonding. The roughness less than Ra=1 nm is necessary for the Si-Si wafer direct bonding.
