The atomic-scale understanding of plasma/beam-surface interaction during plasma etching processes is of significant importance in the development of advanced dry etching technologies for microelectronics applications. The etching processes of silicon dioxide (SiO₂), which is widely used as insulator material for interconnect in microchips, is typically done with fluorocarbon plasmas (CF_x). One of the problems that are difficult to understand is the coexistence of both etching and deposition processes caused by carbon atoms. In order to understand such complicated systems, we use MD simulations with empirical potential models. Our model consists of two types of interactions: the covalent bonds and the Van der Waals (VW) interactions. The former is strong (several eV) and of short range, effective only among neighboring atoms. In contrast, the latter is weak (10^-2 eV) and of long range. The range of interaction reaches over more than third neighboring atoms (several Å). The total VW interaction energy is about 10^-1 eV per atom.
We performed two different simulations with and without VW interactions. The deposition of fluorocarbon films are observed only in the cases with VW forces. In the early stage of carbon deposition, small carbon clusters are formed sparsely and they are not bound strongly with each other by covalent bonds, so they can easily depart from the surface without VW interactions. To keep these precursors near the surface to assist the growth of carbon films, the VW interaction is needed.

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