Slurry selectivity to local thickness variations control in advanced Cu CMP process

Color abnormal phenomenon in post Cu chemical mechanical planarization (CMP) is found in 3X nm flash memory. TEM cross-section shows that there is no Cu residue but has localized thickness variation. This color abnormal phenomenon cannot be eliminated with subsequently Cu and barrier polishing. According to experimental results, the non-uniform inhibitor distribution of Cu slurry issue will enhance the localized Cu dishing profile and lead to thickness variations after barrier polishing. This phenomenon is found especially at high selectivity Cu slurry in advanced Cu CMP process. Color abnormal issue is resolved by implementing the slurry with lower corrosion inhibitor concentration. Although it may have slightly dishing issue after Cu polishing, it can be optimized by subsequent barrier polishing process.