Step height removal mechanism of chemical mechanical planarization (CMP) for sub-nano-surface finish

The step height reduction mechanism of chemical mechanical planarization (CMP) was studied to increase the removal rate of ceria (CeO₂) abrasive, which is based on slurry application to high aspect ratio patterns. Four kinds of nano-abrasives at 0.5 wt% abrasive concentration were prepared, including jet-milled ceria, ball-milled ceria, silica, and colloidal silica. Three kinds of ceria and four kinds of colloidal silica were used to evaluate the removal effect with respect to nano-particle size. The step height reduction was investigated with the edge of a rectangular pattern and the top area of a saw tooth pattern. We found that the removal shapes of the rectangular and saw tooth patterns depended on the nano-particle shapes and sizes. In particular, the spherical abrasive was effective at edge removal in both ceria and silica abrasives, while the smaller abrasive sizes showed good rectangular edge pattern removal after relatively short polishing times. These results can be explained by different friction mechanisms, e.g. rolling and sliding frictions. We conclude that a spherically shaped and small-sized ceria abrasive is effective at increasing the ceria removal rate in high aspect ratio patterns.