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Titanium-containing thin films are widely used in microelectronic device structures such as high-permittivity capacitors, barrier metals, and metal gate structures. ALD technology has replaced PVD and CVD to provide excellent step coverage, accurate film thickness control, and high film quality. Many titanium alkylamides and titanium alkoxides such as Tetrakis(dimethylamino)titanium (TDMAT) and titanium tetraisopropoxide (TTIP) have been used as the ALD precursor, and ALD titanium oxide films were deposited at relatively low temperatures, and the maximum ALD process temperature was approximately 200°C. In general, the electrical characteristics of the dielectric film can be improved by increasing deposition temperature, because the density of the film increases and the impurity concentration decreases. In case of high-temperature deposition, however, the step coverage was poor because of the thermal decomposition of the precursor, resulting in a thicker film on the top surface. Therefore, we need titanium precursors with excellent thermal stability together with high reactivity and sufficient volatility. In the case of zirconium precursors, it was reported that thermal stability of tetrakis(ethylmethylamino)zirconium is improved by replacing an alkylamine group with cyclopentadienyl to form tris(dimethylamino)cyclopentadienyl zirconium [1]. In the present study, we investigated the ALD of titanium oxide using various heteroleptic titanium compounds composed of combinations of different ligands, such as cyclopentadienyl, alkylamino, alkoxy, and linked ligands. Saturation dose and the ALD temperature window were determined by measuring growth rate with different precursor feeding times, oxidizing agent feeding times, and the process temperatures. The reaction mechanism was studied by using in-situ quartz crystal microbalance (QCM) and Fourier transform infrared (FTIR) spectroscopy. The physical and electrical properties of the deposited films were also characterized.
[1] J. Niinistö et al, J. Mater. Chem., 18 (2008) 5243.
