Simultaneous etching of underlying metal oxide and sulfide thin films during Cu₂S atomic layer deposition

Herein, we report the simultaneous etching of selected metal oxide and sulfide underlayers during the atomic layer deposition (ALD) of Cu₂S. The unexpected etch was observed to be prompted by the infiltration of highly mobile Cu⁺ ions from a top ALD Cu₂S layer into underlying films, followed by fragmentation of the underlayers and subsequent outward diffusion of both cations and anions from the underlayers to the Cu₂S surface. A strong correlation was observed between the susceptibility to etching, etch rates and the bond dissociation energies of the underlayers. ZnS, ZnO, SnS, and SnO thin films were etched at different rates, while SnO₂ exhibited high resistance to etching. Interestingly, the etch process exhibited self-limiting characteristics dependent on the Cu precursor and H₂S gas dose times, thus indicating simultaneous Cu₂S ALD and controlled sublayer etching reactions. Based on the findings, we proposed a possible mechanism by which the etching proceeds. We further explored, the synthesis of 3-dimensional Cu₂S/ZnO and Cu₂S nanowires using ALD Cu₂S and the observed ZnO etching phenomenon.