Chemical Mechanical Polishing of In-Situ-Doped Polysilicon for MEMS Applications

The present work presents a 200 mm wafer-scale single step industrial Chemical Mechanical Polishing (CMP) process to polish in situ doped polysilicon using a commercial silica-based slurry. By tuning CMP operating conditions and pad conditioning, the surface roughness is reduced uniformly across the wafer down to Rq = 0.22 nm. The observed trends suggest that, within the investigated process window, slurry chemistry plays a role in achieving the lowest roughness, while pad conditioning strongly influences polishing uniformity. In particular, gentler conditioning parameters and less aggressive disk lowers nanoscale surface roughness and improves wafer-scale uniformity. A minimum material removal is required to reach the lowest roughness. Beyond this threshold, Rq remains stable and independent of additional removal. The same behavior is observed over four different ISDP film materials, regardless of the film thickness or post-deposition annealing. Hydrophobic direct bonding of a polished ISDP wafer to a monocrystalline silicon one, yielded defect free interface and high bond strength, demonstrating the potential of the ISDP CMP process to produce surfaces compatible with demanding wafer level packaging requirements.