ИСТИНА

Atomic layer etching (ALE) is a technique for cyclical removing thin layers of material (one to several atomic layers per iteration) using sequential steps of (almost) self-limiting reactions [1,2]. As an alternative to continuous etching, ALE provides significantly higher accuracy, producing much less roughness on the resulting surface and almost no contamination of the material. Moreover, ALE able to reduce existing roughness, which could be applied as inter-step polishing [3,4]. Every ALE cycle consists of at least two self-limiting sequential steps: modification of the surface and removal of modified layer [1–3]. In Plasma Enhanced ALE the removal step is almost always sputtering by a noble gas’ ions, while the modification step is deposition of chemical radicals, bounding only with the first atomic layer of material or forming a thin film on the surface. During modification, the reagent could be deposited on the chamber’s walls. Such a contamination increases the total amount of chemical compound in the chamber and creates a source of radicals during the sputtering, which violets repeatability of the process from step to step and could even convert PEALE to RIE. Considering all the above, in this work we have found PEALE recipes, consisting of three principal steps: deposition of fluorocarbon film from C4F8-plasma, sputtering by Ar+ ions and O2-plasma cleaning. The experiments were conducted in an ICP-chamber, manufactured by JSC «Research Institute of Precision Machine Manufacturing». Sputtering rate measurements were made in-situ with a laser ellipsometer, while various plasma diagnostics were used to accurately determine plasma parameters and chemical composition of the discharge. The resulting recipes show unprecedented repeatability and precision (fig. 1.: 3 atomic layers per cycle regime was repeated 20 times, the other two 40 times).