Etching characteristics and mechanism of Ba_0.7Sr_0.3TiO₃ thin films in an inductively coupled plasma

The inductively-coupled-plasma (ICP) etching behavior of B_0.7Sr_0.3TiO₃ (BST) thin films has been characterized with Cl₂/CF₄, Cl₂/SF₆ and Cl₂/Ar gas mixtures. CF₄ and SF₆ were found to impede the etch process, presumably due to competition between plasma deposition and etching. A chemically assisted etch of BST was obtained under various Cl₂/Ar gas mixtures. The etch profile along with etch anisotropy was observed as a function of etching parameters by scanning electron microscopy. The surface morphologies after etching were analyzed by atomic force microscopy. A smooth surface (roughness ∼1.8nm) with no residue was observed under 30%Cl₂ in Ar/Cl₂, ICP power of 1 kW, substrate bias of 500V, and 10mTorr. To clarify the etching mechanism, the surface reaction of the BST thin films was investigated by X-ray photoelectron spectroscopy. It was found that Ba was mainly removed by chemically assisted physical etching (possible products such as BaCl_x). Physical bombardment is more effective than Cl chemical reaction for removing Sr, while Ti can almost be removed by chemical reaction (such as TiCl_x). The etching results described correlate well with the thermochemical calculations.