7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Wet-like plasma for the next generation of atomic layer etching

Thi-Thuy-Nga Nguyen1, Kazunori Shinoda2, Hirotaka Hamamura2,Kenji Maeda3, Kenetsu Yokogawa3, Masaru Izawa3, Kenji Ishikawa1, and Masaru Hori1
1Nagoya University, Japan, 2Hitachi, Ltd., Japan, 3Hitachi High-Tech Corp., Japane-mail (speaker): nguyen@plasma.engg.nagoya-u.ac.jp

In the fabrication of next-generation field effecttransistor (FET) of logic semiconductor devices, thedevice size has been downscaled to several nanometers.
Hence, selective etching of metal gate layer made oftitanium compound such as ternary metal carbide TiAlC,metal nitride TiN, or metal alloy TiAl is a challenge andrequires a high-performance etching technology. In ourdevelopment of advanced etching methods, we haveproposed the wet-dry etching or wet-like plasma etchingthat combines the advantages of wet etching (highisotropy and selectivity) and dry etching (highcontrollability). By using a floating wire-assisted vapor
plasma at medium pressure, a wet-like plasma containing
high-density reactive radicals can be remotely generated,
this significantly increases the chemical reaction rate to
the sample surface.
In traditional dry etching, halogen plasma etchants formetal and metal compounds have been used. For TiAlC
material, fluorine-based plasma is not a good candidate
due to forming a non-volatile product AlF3 (boiling point(b.p.) more than 1290 °C). Chlorine-based plasma, that isnormally toxic and corrosive, can form the volatile
product such as AlCl3 (b.p. ~ 183 °C); however, the samevolatile product TiCl4 (b.p. ~ 136 °C) causes poor
selective etching. Here we investigate using non-halogen
vapor plasmas to open a wide-range selection ofenvironment-friendly etchants for highly selective
formation of volatile products.

For dry atomic layer etching (ALE) processes such asplasma-ALE and thermal-ALE, surface modification isused to reduce surface energy of sample surface in thefirst step, and the modified layer with lower surface
energy is removed in the next step. Here we propose anew ALE process using wet-like plasma for surface
modification of metal compounds such as TiAlC by
floating wire-assisted Ar/NH4OH vapor plasma at
medium pressures ranged from 0.2 kPa to 50 kPa. The
high-density plasma containing NH, H, and OH canmodify TiAlC surface to form volatile compounds
having chemical bonds such as methyl (Al–CH3) andmethylamine (Ti–N-CH3). By controlling the surface
reactions, selective removal of TiAlC over TiN and TiAl
can be achieved by the reaction with N-H-O plasma.
Therefore, the wet-like plasma etching opens a new way
to approach highly selective etching of metal and metalcompounds with both isotropic and anisotropic behaviors
for the next generation of atomic layer etching.
References[1] T.T.N. Nguyen, M. Sasaki, S.N. Hsiao, T. Tsutsumi,
K. Ishikawa, and M. Hori, Plasma Process. Polym. 19, 6(2022).
[2] T.T.N. Nguyen, K. Shinoda, H. Hamamura, K. Maeda,
K. Yokogawa, M. Izawa, K. Ishikawa, and M. Hori, Sci.
Rep. 12, 1 (2022).

Fig. 1. Atomic layer etching of metal carbide using a wet-like plasma of Ar and NH4OH vapor.