Characterization and reduction of copper chemical-mechanical-polishing-induced scratches

The formation of scratches during the chemical mechanical polishing (CMP) of Copper (Cu) interconnects is inevitable. As interconnect dimensions shrink with each successive technology node, the impact of these CMP induced scratches is expected to become more severe. A three-step Cu CMP process was investigated in terms of scratch formation on the various polishing platens. Two characteristic types of microscratches can be found after the Cu CMP process. They are long microscratches and triangle microscratches. The study shows that the microscratches generated by platen 1 tend to be deeper than those generated by platen 2, and they can remain even after passing through platens two and three. The effects of polishing pressure and polishing speed on microscratch formations are unclear. Therefore, the most likely reason for platen 1 generating deeper microscratches is due to the use of larger and harder abrasive particles. In addition, it was also noticed that the occurrence of microscratches could increase due to the agglomeration of alumina abrasive particles into larger particles. Flushing off the stagnant slurry in the slurry line to remove the agglomerated abrasive particles prior to actual polishing is effective in reducing the incidence of scratching.