Nano-scratch evaluations of copper chemical mechanical polishing

Nanoscale scratches are applied using an atomic force microscope (AFM) to investigate the mechanical aspect of the material removal process in chemical–mechanical polishing. The scratching experiments are carried out with the AFM, whose probe has an SiO2 particle (radius ~ 400 nm) bonded to it, at low normal forces in deionized (DI) water and a slurry. The experimental results show that the scratch depth increases with increasing normal force. Under a constant force, the scratch depth of the surface in the slurry is significantly larger than that in DI water. This is due to a soft passivation layer generated during chemical interactions on the copper surface. The passivation layer significantly affects the coefficient of friction (COF) and wear rate. At a low scratch depth (below 20 nm), the COF obtained in DI water is ~ 1.74 times larger than that obtained in the slurry. The wear rate obtained in the slurry is larger than that obtained in the DI water.

► Material removal of chemical–mechanical polishing is explored by nano-scratch testing.
► Scratch profiles and applied forces depend on the generation of passivation layer.
► The scratch depths increase with the generation of passivation layer in the slurry.
► The coefficient of friction in the slurry is smaller than that in deionized (DI) water.
► The wear rate in the slurry is significantly larger than the wear rates in the DI water.