Case study for particle agglomeration during chemical mechanical polishing process

Over sized particles in spent slurry are analyzed to examine particle agglomeration during chemical mechanical polishing process. In tungsten (W) polishing, due to greater chance of collision for large particles, high abrasive content slurries yield less oversized particles during polishing. However, in oxide wafer polishing, fumed silica follows the similar agglomerating behavior as in tungsten polishing, while colloidal silica shows a reversed trend. Defectivity measurements on oxide wafer confirm the correlation between spent slurry large particle count (LPC) and defects number on wafers, which means agglomerates produced during polishing process may cause defects in CMP.