The Effects of Post Chemical Mechanical Planaization Buffing on Defect Density of Tungsten and Oxide Wafers

Abstract

Tungsten sheet wafers and tetraethylorthosilicate (TEOS) wafers were planarized on chemical mechanical planarization (CMP) tools and cleaned using a mechanical wafer cleaner. Post‐CMP buffing processes on the primary or secondary polisher platens were investigated. Using laser scattering wafer inspection systems and atomic force microscopy we demonstrated that the buffing process strongly affects the defect density on both the TEOS and tungsten CMP wafers and the roughness power spectrum 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 density. The changes in zeta potential of the slurry particles and the TEOS 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 densities measured on the same TEOS wafers using SFS6220 and SFS6420 were compared. The results indicated that some of the defect counts may be attributed to the intrusion defects and background noise from the surface roughness.