Study on Cu Dishing in CMP Process and Its Impact on Hybrid Bonding by Pad size

Cu/SiO2 Hybrid bonding has become a critical technology for advanced semiconductor packaging, enabling fine-pitch interconnects with superior electrical and mechanical performance. However, achieving high-quality Cu-to-Cu bonding requires perfectly flat surfaces, which are often compromised by Cu dishing during chemical mechanical polishing (CMP). In this study, we systematically investigated the effect of Cu pad size (4, 6, 8, and 10  µm) and spacing on Cu dishing behavior and hybrid bonding quality. Larger Cu pads exhibited significantly greater Cu dishing, resulting in incomplete Cu-to-Cu bonding. In contrast, smaller pads showed minimal Cu dishing and enabled uniform, void-free bonding interface. In addition, the flatness of the SiO₂ surface was also critical, as non-uniformity caused by SiO₂ recess after Cu CMP adversely affected the bonding quality. Both the extent of Cu dishing and the planarity of the SiO₂ surface are critical factors in achieving high-quality, reliable hybrid bonding.