Etching characteristics and mechanism of Ba0.7Sr0.3TiO3 thin films in an inductively coupled plasma

The inductively-coupled-plasma (ICP) etching behavior of Ba0.7ST0.3TiO3 (BST) thin films has been characterized with Cl-2/CF4, Cl-2/SF6 and Cl-2/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 Cl-2/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 similar to 1.8 nm) with no residue was observed under 30%Cl-2 in Ar/Cl-2, ICP power of 1 kW, substrate bias of 500 V, and 10 mTorr. 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 BaClx). Physical bombardment is more effective than Cl chemical reaction for removing Sr, while Ti can almost be removed by chemical reaction (such as TiClx). The etching results described correlate well with the thermochemical calculations.