Etching Characteristics and Mechanism of Ba0.7Sr0.3TiO3 Thin Films in an Inductively Coupled Plasma

The inductively-coupled-plasma (ICP) etching behavior of Ba0.7Sr0.3TiO3 (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 ∼1.8 nm) with no residue was observed under 30%Cl2 in Ar/Cl2, 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 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.