Evaluation of Digital Holography Microscopy for Roughness Control Prior Wafer Direct Bonding

Direct surface bonding of wafers in 3D integration requires perfectly smooth surfaces, with roughness values below 1 nm, usually characterized with Atomic Force Microscopy. An alternative technique, Digital Holography Microscopy is evaluated here and shown to be precise enough to differentiate adequate wafers, that is chemical mechanical polished, from non treated ones.