Minimizing Recess of Cu Pad on Hybrid Bonding with SiCN via Non-selective Chemical Mechanical Polishing and Post-cleaning Steps

Abstract

Hybrid bonding has become a promising approach to realizing fine pitch interconnection via bonding for both the wafer level and die level. The morphology and cleanliness of the bonding surface are critical to ensure a high yield. Therefore, surface planarization by chemical mechanical polishing (CMP) is considered a key process. The recess on the Cu pad must be controlled to be less than 5 nm by adjusting the removal rate between the Cu, the barrier layer, and the bonding dielectric layer. Conventionally, SiO2 has served as the bonding dielectric. However, SiCN is considered a promising dielectric because of its high bonding strength, suppression of voids, and ability to function as a Cu diffusion barrier. Here, we investigated simultaneous Cu, barrier, and SiCN CMP for hybrid bonding. Post-CMP processes such as cleaning and activation were also assessed. The results revealed that the removal rate of the three materials could be adjusted by dilution of the slurry and oxidizer. Lower selectivity was achieved at a certain dilution rate in an alkaline barrier slurry. Plasma activation revealed that the Cu passivation layer formed during cleaning was removed. Therefore, residues from CMP and post-CMP processes did not affect Cu prior to the hybrid bonding.