Study and Improvement on Tungsten Plug Corrosion in CMP Process for PCRAM

To reduce the reset current for developing reliable high density phase change random access memory (PCRAM), small bottom electrode contact (BEC) size formation is a critical process. One of the failure mode for the process is the corrosion of tungsten plug, which is caused by tungsten chemical mechanical planarization (CMP) process. In this paper, this CMP process was analyzed. The tungsten polishing step process was characterized by the coefficient j and it shows good performance in tungsten polishing process. The alkali and acidic buff slurry effect on tungsten plug performance were studied. The result shows that the recess free tungsten plug had been fabricated with acidic buff slurry. The electric results confirm that it can fulfill the set operation of PCRAM cells.