Silica Particle Contamination and Cleaning in Molybdenum CMP

Molybdenum (Mo) is a promising replacement for Tungsten (W) in advanced semiconductor nodes due to its low resistivity and the elimination of the need for a barrier layer. Silica particle-based acidic slurries are commonly used in the chemical mechanical polishing (CMP) process, but complete removal of these particles is critical for subsequent processes. This study investigated particle contamination and cleaning mechanisms to develop effective cleaning solutions. Mo films were polished using H 2 O 2 as an oxidizer and colloidal silica as an abrasive under varying down pressures and rotation speeds to induce contamination. Dipping cleaning for 60 seconds in de-ionized water, 2 wt% ammonia, and potassium hydroxide (KOH) solutions were performed to evaluate particle removal efficiency. High oxidizer concentration and high slurry temperature were found to result in low cleaning efficiency. Mechanical friction effects, including the rotation speeds of the carrier head and platen and the down pressure of the carrier head, were also studied. Optimal conditions of 93 rpm platen speed, 87 rpm carrier head speed, and 1 psi down pressure yielded the fewest remaining particles after cleaning.