Etching characteristics and mechanism of Ga-doped ZnO thin films in inductively-coupled HBr/X (X = Ar, He, N2, O2) plasmas

We investigated the etch characteristics and mechanisms of Ga-doped ZnO (Ga–ZnO) thin films in HBr/X (X = Ar, He, N2, O2) inductively-coupled plasmas. The etch rates of Ga–ZnO thin films were measured as a function of the additive gas fraction in the range of 0–100% for Ar, He, N2, and O2 at a fixed gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). The plasma chemistry was analyzed using a combination of the global (zero-dimensional) plasma model and Langmuir probe diagnostics. By comparing the behavior of the etch rate and fluxes of plasma active species, we found that the Ga–ZnO etch process was not limited by ion-surface interaction kinetics and appeared in the reaction rate-limited etch regime. In the HBr/O2 plasma, the etch kinetics were probably influenced by oxidation of the etched surface.

► Ga-ZnO etching mechanism was analyzed by combination of plasma diagnostics and plasma model. ► Ga–ZnO etch rates was monotonically decreased with increasing additive gas fraction. ► Ga–ZnO etch process was limited by reaction rate-limited etch regime.