Polysilicon gate etching in high density plasmas. III. X-ray photoelectron spectroscopy investigation of sidewall passivation of silicon trenches using an oxide hard mask

Abstract
The characteristics of poly-Si trench etching in high density plasma processes was studied by x-ray photoelectron spectroscopy. Poly-Si films on SiO2-covered Si(100) substrates were masked with a 200-nm-thick oxide hard mask. The 200 mm wafers were then etched downstream using a helicon high density plasma source and a chlorine-based gas chemistry. After etching, samples were transferred under ultrahigh vacuum to a surface analysis chamber equipped with an x-ray photoelectron spectrometer. Regular arrays of trenches were used to determine the photoelectron signals originating from the tops, sidewalls, and bottoms of the features. A thin oxide film was found on the sides of the oxide masked poly-Si trenches. The origin of this film can be related to the sputtering and redeposition of oxide from the quartz tube of the helicon source located in the plasma generation region. A substantial amount of chlorine was present on the poly-Si sidewall of the features, whereas less chlorine was found on the oxide surfaces. The poly-Si sidewalls were covered by a small amount of oxygen.

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