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Atomic layer deposition (ALD) of TiO2 thin films using Ti isopropoxide and tetrakis-dimethyl-amido titanium (TDMAT) as two kinds of Ti precursors and water as another reactant was investigated. TiO2 films with high purity can be grown in a self-limited ALD growth mode by using either Ti isopropoxide or TDMAT as Ti precursors. Different growth behaviors as a function of deposition temperature were observed. A typical growth rate curve-increased growth rate per cycle (GPC) with increasing temperatures was observed for the TiO2 film deposited by Ti isopropoxide and H2O, while surprisingly high GPC was observed at low temperatures for the TiO2 film deposited by TDMAT and H2O. An energetic model was proposed to explain the different growth behaviors with different precursors. Density functional theory (DFT) calculation was made. The GPC in the low temperature region is determined by the reaction energy barrier. From the experimental results and DFT calculation, we found that the intermediate product stability after the ligand exchange is determined by the desorption behavior, which has a huge effect on the width of the ALD process window.

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Atomic layer deposition ͑ALD͒ of TiO 2 films from tetrakis͑dimethylamido͒ titanium ͑TDMAT͒ or titanium tetraisopropoxide ͑TTIP͒ precursors was investigated. The growth kinetics, chemical composition, and crystallization behavior of the TiO 2 films were compared for combinations of the two precursors with three different sources of oxygen ͓thermal ALD using H 2 O and plasma-enhanced ALD ͑PEALD͒ using H 2 O or O 2 plasma͔. For TDMAT, the growth rate per cycle ͑GPC͒ decreased with increasing temperature; while for TTIP with either water plasma or O 2 plasma, a relatively constant growth rate per cycle was observed as a function of substrate temperature. It was found that the crystallization temperature of the TiO 2 films depends both on film thickness and on the deposition conditions. A correlation was observed between the TiO 2 crystallization temperature and the C impurity concentration in the film. The TiO 2 films grown using a H 2 O plasma exhibit the lowest crystallization temperature and have no detectable C impurities. In situ X-ray diffraction measurements were used to test the diffusion barrier properties of the TiO 2 layers and proved that all TiO 2 films grown using either H 2 O or O 2 plasma are dense and continuous.

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Vanadium pentoxide was deposited by atomic layer deposition (ALD) from vanadyl-tri-isopropoxide (VTIP). Water or oxygen was used as a reactive gas in thermal and plasma-enhanced (PE) processes. For PE ALD, there was a wide ALD temperature window from 50 to 200°C . Above 200°C , VTIP decomposed thermally, resulting in the chemical vapor deposition (CVD) of vanadium pentoxide. The PE ALD reactions saturated much faster than during thermal ALD, leading to a growth rate of approximately 0.7 Å/cycle during PE ALD using normalH2O or normalO2 . Optical emission spectroscopy showed combustion-like reactions during the plasma step. X-ray diffraction was performed to determine the crystallinity of the films after deposition and after postannealing under He or normalO2 atmosphere. Films grown with CVD at 300°C and PE normalO2 ALD at 150°C were (001)-oriented normalV2normalO5 as deposited, while thermal and PE normalH2O ALD films grown at 150°C were amorphous as deposited. The crystallinity of the PE normalO2 ALD could be correlated to its high purity, while the other films had significant carbon contamination, as shown by X-ray photoelectron spectroscopy. Annealing under He led to oxygen-deficient films, while all samples eventually crystallized into normalV2normalO5 under normalO2 .