Abstract
In this work, we have investigated the evolution of line roughness from e-beam lithography to final gate patterning based on conventional SiO<sub>2</sub>/Si<sub>3</sub>N<sub>4</sub>/SiO<sub>2</sub> (ONO) hard mask using a Capacitively Coupled Plasma (CCP) etcher. A severe roughness was observed on gate patterning line when PR patterns were directly transferred into ONO hard mask even if a high etch selectivity of ONO hard mask to PR was used by CF<sub>4</sub>/CH<sub>2</sub>F<sub>2</sub>/Ar plasma. The formation mechanisms of line roughness were presented by a) effect of decomposed oxygen radical from bulk SiO<sub>2</sub> by ion bombardment, b) rough surface morphology of poly-silicon accelerates etch of both hard mask and PR sidewalls by reflected ion. It is found that a combination of a capping layer and α-Si gate can reduce strong dependence on PR mask and eliminate ion reflection effect from rough surface morphology. Our results show that gate pattern indicates a smooth line without deformation and final gate length of 29nm with Line Width Roughness of 3.5nm is achieved.
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