Yong-Pil Han

Effects of nonionic surfactants on oxide-to-polysilicon selectivity during chemical mechanical polishing

The effects of surfactants on oxide-to-polysilicon selectivity during chemical mechanical polishing have been investigated. Slurries with nonionic surfactants such as Brij surfactants, polyethylene oxide (PEO), and ethylene oxide-propylene oxide-ethylene oxide triblock copolymer enhanced oxide-to-polysilicon polishing selectivity. Although a current conventional oxide slurry has a low oxide-to-polysilicon selectivity of 0.5:1, slurries with nonionic surfactants show a higher selectivity due to a combined effect of adsorption and interfacial adhesion of added nonionic surfactant molecules on the polysilicon surface. The oxide-to-polysilicon selectivity of the Brij surfactant added slurry displayed a stronger dependency on the hydrophile-lipophile-balance (HLB) value than the type of alkyl group or the chain length of surfactants. Especially, Brij52 with low HLB value gave an oxide-to-polysilicon selectivity of 9.3, which is 17 times higher than the selectivity of a commercial oxide slurry. A high molecular weight polymeric surfactant such as PEO also gave a greater selectivity than a low molecular weight surfactant. In addition, slurries with nonionic surfactants reduce the final thickness variation effectively in damascene structure having a polysilicon stopping layer. The final thickness variation polished with the Brij52 added slurry was decreased to one fourth of that with the conventional oxide slurry only.