Rapid thermal-cyclic atomic-layer etching of titanium nitride in CHF 3 /O 2 downstream plasma

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Abstract
Isotropic atomic-layer etching (ALE) of TiN—by using a plasma-assisted thermal-cyclic process with a 300-mm tool—was demonstrated. The process consists of exposure to a downstream CHF 3 /O 2 plasma (for surface modification) followed by infrared irradiation for thermal desorption of the modified surface. Etched amount of TiN per cycle saturated at around 0.6 nm/cycle with respect to both radical-exposure time and infrared-irradiation time. To examine the reaction mechanism of the cyclic etching, the surfaces of TiN samples after CHF 3 /O 2 plasma exposure were analyzed by in situ x-ray photoelectron spectroscopy (XPS). Self-limiting formation of the surface-modified layer, which was tentatively identified as an ammonium salt such as (NH 4 ) x TiF y   , was observed after radical exposure. It was confirmed by in situ XPS that the surface-modified layer was removed after thermal annealing at 110 °C. Isotropic ALE of TiN was thus demonstrated by using formation and desorption of ammonium salt in CHF 3 /O 2 downstream plasma, which was also used for isotropic ALE of Si 3 N 4 .

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