Fluorocarbon based layer-by-layer etching of Si and SiO/sub 2/ - A molecular dynamics investigation

Summary form only given. As the critical dimensions in microelectronics devices shrink below 20 nm, it is becoming essential to control plasma etching processes on a sub-nm scale. Although atomic layer etching (ALE) techniques provide such dimensional precision, ALE etch rates are slow enough to be impractical for commercial applications. In this paper, we use a molecular dynamics (MD) model to investigate layer-by-layer etching of SiO₂ and Si using low to moderate energy fluorocarbon and Ar⁺ ions. The following process sequence is examined: a. Deposition of a thin fluorocarbon layer on the material surface using low energy CF₂ ⁺ or CF₃ ⁺ ions, b. Use of Ar⁺ ions to remove a material layer whose thickness is commensurate with the F on the surface. As the fluorocarbon passivation layer will be a few Aring thick, it is expected that more than one atomic layer will be etched during each step and the surface might become rough on an atomic scale. The goal is not ALE per se but layer-by-layer etching of the material in a manner that dimensions can be controlled on a sub-nm scale. Characteristics of the fluorocarbon passivation layer are examined in this paper, and the role on Ar⁺ ion energy on etching properties is investigated. The computational MD model used in the present study has been described in detail in [V.V. Smirnov, et al., J. Appl. Phys. 97, 093302 (2005)]. This MD model takes into account the interactions between Si, O, C and F. In the model, the pseudo-potentials for 2 and 3-body interactions have either been obtained from the literature or computed using ab-initio techniques utilizing Gaussian98. The Stillinger-Weber potential construct has been used to represent the pseudo-potentials and the velocity-Verlet algorithm is used to advance particle trajectories. Following ion impact, material temperature is controlled using the Berendsen thermal bath model. Computations show that the fluorocarbon passivation layer is a few Aring thick, its thickness increases with fluorocarbon ion energy, and CF₂ ⁺ ions produce a thicker layer than CF₃ ⁺ ions. When Ar⁺ ions with energy less than 50 eV are bombarded on SiO₂, SiO₂ is etched only as long as F is available near the surface for reactive ion etching