Atomic Layer Deposition, Characterization, and Growth Mechanistic Studies of TiO₂ Thin Films

Abstract

Two heteroleptic titanium precursors were investigated for the atomic layer deposition (ALD) of titanium dioxide using ozone as the oxygen source. The precursors, titanium (N,N'-diisopropylacetamidinate)tris(isopropoxide) (Ti(O(i)Pr)3(N(i)Pr-Me-amd)) and titanium bis(dimethylamide)bis(isopropoxide) (Ti(NMe2)2(O(i)Pr)2), exhibit self-limiting growth behavior up to a maximum temperature of 325 °C. Ti(NMe2)2(O(i)Pr)2 displays an excellent growth rate of 0.9 Å/cycle at 325 °C while the growth rate of Ti(O(i)Pr)3(N(i)Pr-Me-amd) is 0.3 Å/cycle at the same temperature. In the temperature range of 275-325 °C, both precursors deposit titanium dioxide in the anatase phase. In the case of Ti(NMe2)2(O(i)Pr)2, high-temperature X-ray diffraction (HTXRD) studies reveal a thickness-dependent phase change from anatase to rutile at 875-975 °C. X-ray photoelectron spectroscopy (XPS) indicates that the films have high purity and are close to the stoichiometric composition. Reaction mechanisms taking place during the ALD process were studied in situ with quadrupole mass spectrometry (QMS) and quartz crystal microbalance (QCM).

Ozone‐Based Atomic Layer Deposition of Gd2O3 from Tris(isopropyl‐cyclopentadienyl)gadolinium: Growth Characteristics and Surface Chemistry

“…The absence of the parasitic CVD reaction (and the much improved WiWNU) also suggests the suppression of non‐uniform sorption reactions with H 2 O generated during combustion. While the impact of the presence of NO x as an admixture in O 3 in the gas phase on the surface chemistry of metal oxides has not been studied in detail before, it is instructive to compare the above results to reports on O 3 ‐based ALD using N‐containing precursors, such as amides or amidinates . In such processes, NO x is formed as a reaction product of the precursor combustion during the O 3 exposure .…”

Titanium dioxide thin films by atomic layer deposition: a review

“…For the Ti(Cp)(CHT)/O3 process, the rutile content progressively increases starting from 300 o C being higher than the anatase content above 325 o C [791]. For amidinate-based processes the crystallization onset is similar such that the films fabricated using Ti(O i Pr)3(N i Pr-Me-amd) and H2O reactants crystallize in the anatase phase at 250-375 o C [776], while use of O3 as the oxygen source increases the onset of the crystallization slightly to 275 o C [777]. For guanidinate precursors the film crystallization takes place at slightly higher temperatures, at 275 o C for the O3-based process and at 300 o C for the H2O-based process, when Ti(NEtMe)3(guan-NEtMe) is used as the Ti precursor [790].…”

“…The films had anatase structure at 275 o C and above, and the carbon impurities were reported to be below the detection limit. Film purity was good and the films were stoichiometric regardless of the decomposition at 375 o C [777]. Ti(O i Pr)3(N i Pr-Me-amd) has the benefit of being liquid, hence avoiding particle incorporation into the films [776].…”

Stability and Surface Reactivity of Anatase TiO2Films

“…27 It is apparent that the preparation method plays an important role in the prevalence and stability of the various TiO 2 phases. As anatase TiO 2 is the desirable phase for a number of applications, a reproducible formation technique for stable anatase phase is very valuable.…”