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

We improved a through-silicon via (TSV) reveal process comprising direct Si/Cu grinding (simultaneous grinding of Si and Cu) and residual metal removal. In this improved process, direct Si/Cu grinding was performed by using a novel grinding wheel (vitrified-bond type) and cleaning the wheel with a high-pressure micro jet. Instead of electroless Ni-B plating, electroless Sn plating was then performed to cover the Cu surface in the TSVs. Finally, alkaline etching of Si was performed to reduce the slight Cu contamination generated by the direct Si/Cu grinding. The Sn film acted not only as a protective layer but also as a direct bonding material for 3D chip stacking. Time-of-flight secondary ion mass spectrometry analysis showed the Cu contaminant concentration at the Si region to be below 5×10
¹⁰
atoms/cm
²
even when the electroless plated Sn film was used. We also performed 3D stacking of a 35-μm-thick Si chip using TSVs revealed by this improved process. As a result, a very thin chip could be simply stacked without any damage. These results demonstrate that this process enables simple 3D integration without Cu contamination.