Following the planarization of the bulk copper and the Ta-based liner, the Final Oxide Chemical Mechanical Planarization (CMP) step prepares the wafer surface for Direct Bond Interconnect (DBI) P3.In a 40nm Back-Side Illuminated (BSI) CMOS Image Sensor integration flow, this step ensures an ultra-smooth and highly planar dielectric surface necessary for subsequent CIS and ISP wafer bond pairing A2.The hybrid bonding process requires sub-nanometer surface roughness to facilitate spontaneous van d