Cu CMP process development and characterization of Cu dishing with 1.8 μm Cu pad and 3.6 μm pitch in Cu/SiO2 hybrid bonding

Abstract

A Cu/SiO2 hybrid bonding process was developed on 1.8 μm Cu pad size and 3.6 μm pitch. A Cu dishing profile was achieved with additional fine copper removal and barrier removal chemical mechanical planarization steps (named P2 rework and P3 rework) due to the different removal rate (RR) of Cu to SiO2. With increasing P2 rework time, the Cu dishing could be increased, because the RR of Cu was larger than that of SiO2. With increasing P3 rework time, the Cu dishing was decreased, which was due to the RR of Cu being lower than that of SiO2. The interface of Cu–Cu bonding with different Cu dishing after 350 °C annealing was studied. By choosing a proper Cu dishing value which is less than the Cu expansion in the 350 °C annealing, the daisy chain resistance per link of 1.2–1.5 Ω and 95% yield of 1000 daisy chain were achieved.