Abstract
In sub-micron ULSI device manufacturing, the conventional chemical mechanical polishing (CMP) process uses various slurries, abrasives, and polishing pads. Recently, however, several difficulties and limitations have been reported in this CMP process. The problems are laid on unstable slurries, scratches onto the surface, various metal contaminants, the dishing features, post-cleaning difficulties, selectivity problem, and high costs for equipment and process maintenance. To overcome these technical issues, electro-chemical polishing which removes copper atoms by electrochemical etching could be a candidate for replacement of CMP process. In ECP process, the copper complexes to be produced by electrochemical reactions are polished by a polishing pad. We have performed the electrochemical polishing (ECP) on the patterned copper layer in alkali-based solution. Even in alkali-based solution, the 0.23µm vias and 3µm trenches are successfully planarized with the optimized process conditions. The concentration and the composition of the alkali-base solution affect the electrochemical polishing rate and current density applied on copper surface. The planarity and the degree of dishing on the copper layer strongly depend on the composition of the solution and current density profile on copper vias and trenches. The profile of the current density should be carefully controlled by adjusting the cyclic pulse voltage signal. In our ECP process, a clean and scratch-free Cu surface was obtained because no abrasive was introduced during the polishing process. This ECP process in alkali-based solution drastically reduces the processing steps and lowers the process.
