Study of copper residue generated during Cu CMP process: Reduction of copper residue between metal patterns

Copper (Cu) chemical-mechanical polishing (CMP) has been a critical technology for copper damascene manufacturing process for metal interconnects. This paper investigated the mechanism of the copper residue generated during Cu-CMP process. Both electrical testing and various physical measurement techniques have been extensively used for the characterization. For bulk Cu CMP process, the wear surface of the retaining ring caused reduction of the effective down pressure on the wafer, resulting in occurrence of residual copper. For barrier metal CMP process, the protrusion of the copper lines (negative oxide erosion) on the fine pitch line and space array was the main contributor to copper residue on the upper interconnection layer. This paper also examines the effects of slurry selectivity on topography correction and dielectric erosion, in multi-step Cu CMP processes. We proposed an optimal selectivity of Cu/Ta(tantalum)/SiO (0.6/1/0.8) of barrier metal polishing slurry to reduce copper residue between metal patterns and to ensure electrical isolation between neighboring circuit.