THE EFFECTS OF POST CHEMICAL-MECHANICAL PLANAIZATION BUFFING ON DEFECT DENSITY OF TUNGSTEN AND OXIDE WAFERS

Tungsten sheet wafers and tetraethylorthosilicate (TEOS) wafers were p lanarized on chemical mechanical planarization (CMP) tools and cleaned using a mechanical wafer cleaner. Post-CMP buffing processes on the p rimary or secondary polisher platens were investigated. Using laser sc attering wafer inspection systems and atomic force microscopy we demon strated that the buffing process strongly affects the defect density o n both the TEOS and tungsten CMP wafers and the roughness power spectr um density of the tungsten CMP wafers. A pH shock'' to the TEOS wafers during oxide CMP on the primary platen resulted in a high defect dens ity. The changes in zeta potential of the slurry particles and the TEO S surfaces during the pH shock might have caused the variations in the defect density. TEOS wafers polished with a tungsten slurry were also cleaned on a wafer cleaner with diluted HF solutions. The HF solution cleaning further enabled a reduction of the defect density. Defect de nsities measured on the same TEOS wafers using SFS6220 and SFS6420 wer e compared. The results indicated that some of the defect counts may b e attributed to the intrusion defects and background noise from the su rface roughness.