Effects of Nonionic Surfactants on Oxide-to-Polysilicon Selectivity during Chemical Mechanical Polishing

Abstract

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 ͑PEO͒, 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 ͑HLB͒ 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.As the design rule decreases in semiconductor manufacturing industry, multilayer integration using chemical mechanical polishing ͑CMP͒ is being widely adopted to obtain a flat surface during processing. Current CMP processes are focused on meeting a higher planarity and uniformity requirements. As a result, the process windows of CMP processes become tighter. 1-5 In general, high selective slurry to a stopping layer is required to obtain these performances simultaneously. When a high selective slurry is used, effective stop on a stopping layer becomes possible due to the high selectivity of materials. Typical examples of selective polishing with highly selective slurry are shallow trench isolation CMP process with silicon nitride stopper and copper CMP process with tantalum ͑Ta͒ or tantalum nitride ͑TaN͒ stopping layer. 1-7 The concept of selective CMP process is important especially in a damascene structured pattern. When a single material is polished to planarize an oxide layer like interlayer dielectric ͑ILD͒ or intermetal dielectric ͑IMD͒, the selectivity is not critical. 1-4 However, the selectivity to the stopper material is indispensable for uniformity and planarity when two or more materials are polished simultaneously.Polysilicon is one of the candidates as a stopping material for a damascene structure. CMP process with efficient stop on polysilicon requires a improved selective slurry to polysilicon. However, the current conventional oxide slurry composed of fumed silica abrasive does not stop effectively on polysilicon due to the low oxide-topolysilicon polishing selectivity of 0.5:1. To increase...

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