Plasma Etch of IGZO Thin Film and IGZO/SiO₂ Interface Diffusion in Inductively Coupled CH₄/Ar Plasmas

ABSTRACT In this work, the etching characteristics of InGaZnO 4 (IGZO) thin films were systemically investigated in inductively coupled CH 4 /Ar plasmas with various gas ratios, bias voltages, and surface temperatures. The ion flux in the CH 4 /Ar plasmas was analyzed using bias power and voltage, whereas the relative densities of CH and H radicals were quantified through optical actinometry. The change in CH 3 radical density was also estimated based on plasma kinetics analysis. The correlations between the plasma properties and IGZO etch rate were investigated. In CH 4 /Ar plasmas with CH 4 ratios below 80%, the IGZO etch rate increases with a higher CH 4 proportion, aligning with the ascending trend of CH 3 radical density, which suggests that CH 3 radical density acts as a limiting factor (radical‐limited regime). However, the IGZO etch rate decreases when the CH 4 ratio exceeds 80%, corresponding to the reduction in ion flux, which indicates that ion flux becomes a limiting factor in this ion‐limited regime. The IGZO etch rate shows a linear relationship with bias voltage and follows the Arrhenius equation with varying surface temperature in plasmas without bias voltage. A spontaneous etch model was proposed based on these relationships. In this model, the IGZO etch rate depends on CH 3 radical density and IGZO surface reactivity, where ion bombardment contributes more significantly to surface reactivity than high surface temperature. IGZO thin film was deposited on SiO 2 during the fabrication of a 3D stacked ferroelectric field‐effect transistor (FeFET) memory device. The interaction between IGZO and SiO 2 during CH 4 /Ar plasma processing was investigated using time‐of‐flight secondary ion mass spectrometry. The efficacy of removing IGZO atoms that had diffused into the SiO 2 network was enhanced when subjected to plasma with a bias voltage, compared to the process without a bias voltage. However, exposure to CH 4 /Ar plasma resulted in a deeper diffusion of IGZO atoms into the SiO 2 network, primarily attributed to ion bombardment rather than elevated surface temperature. A significant improvement in surface smoothness was achieved after IGZO and SiO 2 etch by introducing BCl 3 into the SiO 2 etching chemistry.