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

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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.