Atomic Layer Deposition of TiO2 Thin Films from Ti(O i Pr)2(dmae)2 and H2O Bull. Korean Chem. Soc. 2004, Vol. 25, No. 4 475 Atomic Layer Deposition of TiO 2 Thin Films from Ti(O i Pr) 2 (dmae) 2 and H 2 O Jae P. Lee, Mi H. Park, Taek-Mo Chung, † Yunsoo Kim, † and Myung M. Sung * Department of Chemistry, Kookmin University, Seoul 136-702, Korea † Advanced Materials Division, Korea Research Institute of Chemical Technology, Yusong, P.O. Box 107, Daejeon 305-600, Korea Received September 31, 2003 TiO 2 thin films were grown on Si (100) substrates by atomic layer deposition using [Ti(OPr i ) 2 (dmae) 2 ] and water as precursors. The thickness, chemical composition, crystalline structure, and morphology of the deposited films were investigated by transmission electron microscopy, UV spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. The results show that TiO 2 ALD using [Ti(OPr i ) 2 (dmae) 2 ] as a precursor is self-controlled at temperatures of 100-300 o C. At the growth temperatures below 300 o C, the surface morphology of the TiO 2 films is smooth and uniform. The TiO 2 film was grown with a preferred orientation toward the [101] direction at 400 o C. Key Words : Atomic layer deposition, TiO 2 , Precursor Introduction Thin films of titanium dioxide (TiO 2 ) have high refractive index, excellent transmittance in the visible and near-IR frequency, and high chemical stability. 1 They have been shown to be useful as anti-reflection coating, sensors, and photocatalysts. 2 The TiO 2 thin film is also a promising material for the development of microelectronics including as an alternative to silicon dioxide in the gate dielectric of metal oxide semiconductor field effect transistors (MOSFETS), due to its high dielectric constant. 3 Moreover, titanium oxide is a constituent of important multicomponent oxides such as BaTiO 3 and SrTiO 3, which are well known to be ferro- electrics. 4 There have been several reports on atomic layer deposition (ALD) of TiO 2 5-9 although TiO 2 films were more frequently prepared by chemical vapor deposition. 10-12 The ALD is a gas-phase thin film deposition method by using self-controlled surface reactions. During the past decade the ALD has attracted considerable attention as a method manufacturing of high-quality thin films and producing tailored molecular structures. 13-16 The ALD method relied on sequential saturated surface reactions which result in the formation of a monolayer in each sequence. The successive self-controlled growth mechanism in the ALD inherently eliminates gas phase reactions. Elimination of gas phase reactions results in emphasizing the importance of surface reaction. As a conse- quence, the ALD process is very sensitive to precursors as well as surface conditions of the substrates. The ALD of TiO 2 thin films has been carried out using TiCl 4 , [Ti(OEt) 4 ], and [Ti(OPr i ) 4 ], as titanium precursors. There are a number of major differences associated with the use of these pre- cursors: the temperature range for the self-controlled growth, growth rate, film crystallinity, and surface morphology. Jones et al. 17 reported on the preparation of TiO 2 thin films using modified alkoxide of titanium, [Ti(OPr i ) 2 (dmae) 2 ] (dmae = dimethylaminoethoxide), as titanium precursor in liquid injection MOCVD and found it to be a better source than other titanium CVD sources previously reported. In the present study, we have investigated the contribution of the precursor, [Ti(OPr i ) 2 (dmae) 2 ], to the growth rate, film crystallinity, and surface morphology in the ALD of the TiO 2 thin films on Si substrates. The precursor, [Ti(OPr i ) 2 (dmae) 2 ], exists as a monomeric complex with pseudo-octahedral coordination at the titanium and has an increased coordi- native saturation at the titanium relative to Ti(OR) 4 compounds, as shown in Figure 1. Therefore, the precursor is more stable in air and moisture than conventional titanium precursors which need to prevent deterioration during storage and use. For comparison, the precursor, [Ti(OPr i ) 4 ], was also used in the ALD of the TiO 2 thin films on Si substrates. Experimental Section Precursor synthesis. The precursor, [Ti(OPr i ) 2 (dmae) 2 ], was prepared by the procedures reported previously. 17 All manipulations were carried out under an inert atmosphere condition using a glove box or standard Schlenk techniques. * Author to whom correspondence should be addressed. e-mail: smm@kookmin.ac.kr Figure 1. The proposed structure of the precursor [Ti(OPr i )2- (dmae)2].