Atomic layer etching (ALE) of silicon nitride with sequential exposure to hydrofluorocarbons and low energy ion bombardment has been demonstrated. The ALE mechanism is generally thought to consist of surface modification via hydrofluorocarbon chemisorption followed by removal of the chemically modified surface layer by ion bombardment, but the underlying details are not fully understood. Using first-principles calculations, we have examined a possible pathway for dissociative chemisorption of CH3F and assessed its potential role in Si3N4 ALE. According to our results, the initial sticking probability tends to be very low (<10−7) even on the H-terminated N-rich surface that is the most reactive towards CH3F, in the absence of dangling bonds. Furthermore, the chemisorption does not significantly modify the strength of surface Si-N bonds or yield a stoichiometrically reasonable pathway for the etching of a full atomic layer. Our findings suggest that reactive species generated from CH3F dissociation and surface activation induced by Ar+ ion bombardment can be key factors in achieving ALE of Si3N4 with CH3F, in contrast to the common explanation of surface chemical modification via direct reaction with CH3F.
Bibliographical noteFunding Information:
This work was supported by Tokyo Electron Limited (TEL) and the R.A. Welch Foundation (No. F-1535). We would like to thank Dr. Peter Ventzek and Dr. Alok Ranjan at Tokyo Electron America for the helpful discussions and suggestions and also the Texas Advanced Computing Center for use of the Stampede2 supercomputing system (OCI-1134872).
© 2020 Elsevier B.V.
- Atomic Layer Etching
- Density functional theory calculation
- Methyl fluoride
- Silicon nitride