Characterization of bonding interface prepared by room-temperature Si wafer direct bonding using the surface smoothing effect of a Ne fast atom beam

Graphical abstractDisplay Omitted We evaluated the characterization of bonding interface between Si surfaces smoothed by Ne FAB surface treatment.The rough surface with a surface roughness of 0.40nm rms was finally decreased down to 0.17nm rms by Ne FAB etching.With Ne FAB smoothing, a bonding energy equivalent to that of the bulk materials was finally attained.Local strain at the bonded interface between surfaces was dramatically decreased by Ne FAB smoothing. We performed room-temperature Si wafer direct bonding by surface activation using a Ne fast atom beam (FAB). The bonding energy between Si wafers prepared by Ne FAB etching is equivalent to that of the bulk materials. We also investigated the surface smoothing effect by Ne FAB etching. A rough Si surface with a surface roughness of 0.40nm rms was etched by Ne FAB, and its surface roughness was decreased down to 0.17nm rms. For a Si surface etched at a depth of 30nm by the Ne FAB, the 1D-PSD (1-dimensional power spectrum density) amplitude was decreased in the range of spatial frequencies >10µm-1. Although the Si wafers with surface roughness of 0.4nm rms could not be bonded, they were successfully bonded after Ne FAB smoothing of etching depths over 5nm, and a bonding energy equivalent to that of the bulk materials was attained. We succeeded in dramatically decreasing the local strain at the bonding interface by the Ne FAB smoothing effect.