Copper CMP Mimicked With Atomic Force Microscopy

To optimize chemical mechanical polishing CMP process, one needs to get information on the interaction between the abrasive slurry particles and the surface being polished. To study such interactions, we used atomic force microscopy (AFM). An AFM tip was used to mimic a single abrasive silica particle typical of those used in CMP slurry. Studying copper CMP, we found that the AFM scanning removes the surface oxide layer in different rates depending on the depth of removal and the pH of the solution. Oxide removal happens considerably faster than the CMP copper removal. This is in agreement with generally accepted models of copper CMP. Both long-range and the friction forces acting between the AFM tip and surface during the polishing process were measured. The correlation between those forces and the removal rate is discussed.