CMP Process Improvement for Non-uniform Cu/SiO₂ Hybrid Bonding Layout

In this work, a 300 mm wafer with Cu pads of 1 μm x 1 μm is used for a hybrid bonding process research. The Cu/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layers were planarized by a three-platen CMP process using different types CMP polishing pads for the Cu recess delta and galvanic corrosion study. The Cu recess is a critical parameter in determining whether wafer to wafer (W2W) hybrid bonding is successful and robust. The non-uniform Cu recess is due to the different antenna ratio of the various Cu pads. CMP polishing pads with various hardness such as soft pads (Shore A: 16.8) and hard pads (Shore D: 54.2 to 67) were evaluated for Cu recess delta and galvanic corrosion study to apply to the W2W hybrid bonding process. Cu CMP pad hardness effect is investigated in the galvanic corrosion study, and it significantly improves Cu recess uniformity for non-uniform hybrid bonding layout.