Surface chemical reactions of etch stop prevention in plasma-enhanced atomic layer etching of silicon nitride

Molecular dynamics (MD) simulations were performed to examine the influence of oxygen (O) ion irradiation at the end of each cycle of plasma-enhanced atomic layer etching (PE-ALE) of silicon nitride (SiN). The main concern during the SiN PE-ALE process is that it can lead to an etch stop due to excessive hydrofluorocarbon (HFC) polymer accumulation, which hinders ion impact in the desorption step. Such an etch stop can be avoided by incorporating an oxygen (O2) plasma irradiation step after the desorption step of a conventional two-step PE ALE process of SiN. In this study, the differences between the two-and three-step PE-ALE processes of SiN with and without O2 plasma irradiation are discussed. In the simulations of this study, low-energy CH2F radicals are deposited on a SiN surface in the adsorption step, and the modified surface is then irradiated with energetic Ar+ ions and removed in the desorption step. In the O2 plasma irradiation step, the resulting surface is irradiated with low-energy O species, and excess carbon (C) atoms are removed. It has been found that the O irradiation step effectively prevents the accumulation of C atoms by promoting the formation of volatile CO molecules.