Mitigating Connected PAD Corrosion in Hybrid Bonding

Abstract

As wafer-to-wafer (W2W) hybrid bonding scales to sub- 500 nm pitches, new reliability challenges emerge, particularly related to connected PAD corrosion. This study investigates the mechanisms and mitigation strategies for connected PAD corrosion observed during the chemical mechanical polishing (CMP) and pre-bonding processes. A dedicated test vehicle was designed to evaluate the influence of layout geometry, metal line length, number of connected pads, and process conditions. Experimental results reveal that metal line length is the dominant factor influencing corrosion severity, with longer connections exhibiting deeper Cu recesses. Process sensitivity studies show that acidic CMP slurries and deionized water rinses exacerbate corrosion due to electrochemical reactions and static charge accumulation. In contrast, alkaline slurry and alkaline water (Kurita water) rinses effectively suppress corrosion by neutralizing surface charge and stabilizing the Cu/dielectric interface. A process partition study confirms that connected PAD corrosion initiates only after barrier layer removal. These findings provide critical insights into the electrochemical and charge-induced mechanisms of connected PAD corrosion and offer practical guidelines for process optimization in advanced hybrid bonding applications.