Fluorocarbon assisted atomic layer etching of SiO₂ using cyclic Ar/C₄F₈ plasma

The authors demonstrate atomic layer etching of SiO₂ using a steady-state Ar plasma, periodic injection of a defined number of C₄F₈ molecules, and synchronized plasma-based Ar⁺ ion bombardment. C₄F₈ injection enables control of the deposited fluorocarbon (FC) layer thickness in the one to several Ångstrom range and chemical modification of the SiO₂ surface. For low energy Ar⁺ ion bombardment conditions, the physical sputter rate of SiO₂ vanishes, whereas SiO₂ can be etched when FC reactants are present at the surface. The authors have measured for the first time the temporal variation of the chemically enhanced etch rate of SiO₂ for Ar⁺ ion energies below 30 eV as a function of fluorocarbon surface coverage. This approach enables controlled removal of Ångstrom-thick SiO₂ layers. Our results demonstrate that development of atomic layer etching processes even for complex materials is feasible.