Abstract
Hafnium(IV) oxide (HfO(2))-based materials have attracted substantial interest owing to their outstanding performance in advanced ultrathin semiconductor devices. However, achieving atomic-level precision and smoothness in HfO(2) etching remains a major challenge, primarily due to the nonvolatility of reaction products formed with halogen-based chemicals at room temperature. Herein, a facile cyclic atomic-layer etching (ALE) process capable of etching HfO(2) films at room temperature without the use of halogen-based chemicals is reported. The ALE process consists of a surface nitrogenation step via N(+)-ion bombardment during N(2) plasma exposure, followed by O(2) plasma treatment to remove the surface-modified layer through the formation of volatile etching byproducts-most likely hafnium nitrates. This process enables precise, subatomic-level etching of HfO(2), achieving an etch depth per cycle ranging from 0.23 to 1.07 Å/cycle, depending on the N(+) ion energy. Additionally, this cyclic ALE method effectively smooths the HfO(2) surface, yielding a 60% reduction in surface roughness after 20 cycles. Based on the proposed mechanism, this facile ALE process can be extended to other transition metal oxides and offers a sustainable route for fabricating advanced functional oxide-based devices, without generating corrosive or toxic wastes.