Grain growth enhancement of electroplated copper film by supercritical annealing

The resistivity increase caused by grain boundary (GB) scattering is a challenging problem in the formation of narrow copper (Cu) interconnects less than 100nm wide. In order to reduce GB scattering, a new annealing method was successfully developed to enhance the grain growth of electroplated Cu films using supercritical (SC) CO₂ with H₂. In order to determine the effect of H₂, the Cu surface was analyzed using X-ray photoelectron spectroscopy (XPS). The amounts of oxygen (O) and carbon (C) at the Cu surface after SC annealing were reduced with increasing H₂ pressure. Surface migration was considered to be enhanced by the reduced amount of O and C, which led to grain growth enhancement. The cross-sectional grain structure in 100-nm-wide interconnect trenches was observed using secondary ion microscopy (SIM). The Cu grains inside the trench were found to be affected by the microstructure in the Cu overburden. Accordingly, Cu grain growth in trenches is also expected to be enhanced by SC annealing.