Improvement of a TSV Reveal Process Comprising Direct Si/Cu Grinding and Residual Metal Removal

We improved a through-silicon via (TSV) revealprocess comprising direct Si/Cu grinding (simultaneousgrinding of Si and Cu) and residual metal removal. In thisimproved process, direct Si/Cu grinding was performed byusing a novel grinding wheel (vitrified-bond type) and cleaningthe wheel with a high-pressure micro jet. Instead of electrolessNi-B plating, electroless Sn plating was then performed tocover the Cu surface in the TSVs. Finally, alkaline etching of Siwas performed to reduce the slight Cu contaminationgenerated by the direct Si/Cu grinding. The Sn film acted notonly as a protective layer but also as a direct bonding materialfor 3D chip stacking. Time-of-flight secondary ion massspectrometry analysis showed the Cu contaminantconcentration at the Si region to be below 5e10 atoms/cm2even when the electroless plated Sn film was used. We alsoperformed 3D stacking of a 35-µm-thick Si chip using TSVsrevealed by this improved process. As a result, a very thin chipcould be simply stacked without any damage. These resultsdemonstrate that this process enables simple 3D integrationwithout Cu contamination.