Development of dishing-less slurry for polysilicon chemical-mechanical polishing process

Dishing of polysilicon and thinning of the stopper silicon nitride films are crucial problems when the polysilicon embedded by low pressure chemical vapor deposition in the trench and the concavity with respective widths of 0.7 mum and 20-100 mum is simultaneously flattened by chemical-mechanical polishing (CMP). In order to suppress these two occurrences, a high polymer compound mixed slurry was developed and characterized. The pH value of the slurry measured on the polishing abrasive pad was decreased by dilution with de-ionized water, which resulted in cohesion and solidification of the slurry. By using this cohered and solidified slurry when the poly silicon surface is flattened by CMP, the dishing thickness of the polysilicon was suppressed to less than 100 nm at a concavity width of 100 mum. The CMP process using the developed slurry is useful for the advanced trench isolation process and is currently applied to NAND flash memory and high-speed bipolar LSI devices.