Angular Dependence of the Etch Rates of TaN in CF4/Ar and CHF3/Ar Plasmas

The etching characteristics of tantalum nitride (TaN), a mask absorber in extreme UV lithography, was investigated by observing the angular dependence of its normalized etch yield in CF 4 /Ar and CHF 3 /Ar inductively coupled plasmas (ICPs). The direction of plasma ions incident on the substrate surface was controlled in a specially designed etcher that contained a Faraday cage and substrate holders of different slope angles. Experiments performed at different ICP powers, combined with analyses of the sample surface by X-ray photoelectron spectroscopy and plasma gases by optical emission spectroscopy, showed that as the ICP power increased, the mechanism involved in the etching of the TaN substrate changed from physical sputtering to chemical sputtering in a CF 4 plasma while the mechanism changed from chemical sputtering to physical sputtering in a CHF 3 plasma. A tantalum native oxide film formed on the substrate surface decreased the etch rates by suppressing the transfer of ionic momentum to TaN. However, hydrogen atoms present in a CHF 3 plasma reduced the thickness of the oxide layer and consequently enhanced the etch rates of the substrate.

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