Focus error reduction by photo-resist planarization in via-first dual damascene process

In order to reduce the focus error for the stacked mask process (SMAP) used in Cu/low-k dual damascene (DD) interconnect, a planarization technology of the under layer film by CMP was developed. Photo-resist was used for the under layer film. CMP slurry with resin abrasive was investigated for the photo-resist planarization. The slurry showed better planarity, lower risk to particle residue, and high selectivity to SiO₂ film. These advantages are attributable to the effects of the particle size and the material characteristics similar to photo-resist. Furthermore, it was found that it is effective for a higher CMP rate to turn the platen and head with lower rotational speed. Using the photo-resist planarization technology, application to via first DD process was investigated. It became clear that focus error reduction of 0.1 μm is confirmed compared with conventional SMAP. The depth of focus (DOF) margin loss due to resist thickness variation caused by via density variation is completely canceled by photo-resist planarization.