20 March 2018 Isotropic atomic level etching of tungsten using formation and desorption of tungsten fluoride
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Abstract
A selective, rapid thermal-cyclic atomic-level etching (ALE) of tungsten is developed. The first step of this process is exposing the surface of tungsten with hydrofluorocarbon plasma at −22°C to form a tungsten fluoride-based surface modified layer on the tungsten surface. The second step is rapid thermal annealing with infrared (IR) irradiation to remove the surface modified layer. Tungsten 4f peaks and a fluorine 1s peak, which were assigned to tungsten fluoride, were observed by in-situ x-ray photoelectron spectroscopy immediately after plasma exposure. The peaks that originated from tungsten fluoride disappeared after the samples were annealed. Cyclic etching tests were carried out by repeating plasma exposure and IR irradiation with a 300-mm ALE tool. Films of tungsten, TiN, and SiO2 were used as sample materials. The amount of etched tungsten increased as the number of cycle repetitions increased. The etched amount per cycle for tungsten was 0.8 nm. In comparison, etching of TiN and SiO2 was not detected. Conformal etching profiles of patterned samples after 60 cycles were obtained. Furthermore, the etched amount per cycle showed saturation behavior with regard to plasma exposure time. Selective, rapid thermal cyclic ALE of tungsten was thus successfully demonstrated.
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Kazunori Shinoda, Nobuya Miyoshi, Hiroyuki Kobayashi, Yuko Hanaoka, Kohei Kawamura, Masaru Izawa, Kenji Ishikawa, Masaru Hori, "Isotropic atomic level etching of tungsten using formation and desorption of tungsten fluoride", Proc. SPIE 10589, Advanced Etch Technology for Nanopatterning VII, 105890I (20 March 2018); doi: 10.1117/12.2297241; https://doi.org/10.1117/12.2297241
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