Selective Atomic Layer Deposition Mechanism for Titanium Dioxide Films with (EtCp)Ti(NMe₂)₃: Ozone versus Water

Abstract

The need for the conformal deposition of TiO 2 thin films in device fabrication has motivated a search for thermally robust titania precursors with noncorrosive byproducts. Alkylamido-cyclopentadienyl precursors are attractive because they are readily oxidized, yet stable, and afford environmentally mild byproducts. We have explored the deposition of TiO 2 films on OH-terminated SiO 2 surfaces by in situ Fourier transform infrared spectroscopy using a novel titanium precursor [(EtCp)-Ti(NMe 2 ) 3 (1), Et = CH 2 CH 3 ] with either ozone or water. This precursor initially reacts with surface hydroxyl groups at ≥150 °C through the loss of its NMe 2 groups. However, once the precursor is chemisorbed, its subsequent reactivities toward ozone and water are very different. There is a clear reaction with ozone, characterized by the formation of monodentate formate and/or chelate bidentate carbonate surface species; in contrast, there is no detectable reaction with water. For the ozone-based ALD process, the surface formate/carbonate species react with the NMe 2 groups during the subsequent pulse of 1, forming TiOTi bonds. Ligand exchange is observed within the 250−300 °C ALD window. X-ray photoelectron spectroscopy confirms the deposition of stoichiometric TiO 2 films with no detectable impurities. For the water-based process, ligand exchange is not observed. Once 1 is adsorbed, there is no spectroscopic evidence for further reaction. However, there is still TiO 2 deposition under typical ALD conditions. Co-adsorption experiments with controlled vapor pressures of water and 1 indicate that deposition arises solely from 1/water gas-phase reactions. This striking lack of reactivity between chemisorbed 1 and water is attributed to the electronic and steric effects of the EtCp group and facilitates the observation of gas-phase reactions.

Chemical Analysis of the Interface between Hybrid Organic–Inorganic Perovskite and Atomic Layer Deposited Al2O3

“…Recently, Klesko et al utilized a similar approach with XPS to calculate the thickness of ALD TiO 2 grown selectively on top of a Si substrate. 66 The thickness of ALD Al 2 O 3 is first inferred in the case of growth on c-Si and is presented in Figure 9a. As expected, the growth behavior of Al 2 O 3 is linear with increasing ALD cycles.…”

Precise Definition of a “Monolayer Point” in Polymer Brush Films for Fabricating Highly Coherent TiO2 Thin Films by Vapor-Phase Infiltration

“…Titanium is an attractive model species for vapor phase brush infiltration given its use in a variety of far reaching applications e.g. TiO2 films are routinely fabricated by solgel 60 , pulsed laser deposition 61 , chemical vapor deposition 62 and ALD 63,64 . TiO2 coatings are widely used in self-cleaning technologies 65 , as an electrode support 66 , as a dielectric medium 67 , and in photocatalysis 68 .…”

“…Moreover, achieving dense inorganic films in a simple one-step inclusion method at low temperatures is very appealing for industrial demands. TiO 2 films are routinely fabricated by sol–gel, pulsed laser deposition (PVD), chemical vapor deposition (CVD), and ALD. , Significantly, a vapor-phase inclusion technique can deposit uniform ultrathin films compared to relatively high-temperature routes such as CVD and PVD. Evaporation and CVD-based techniques cannot achieve high-quality two-dimensional nanofilms with precise thickness control over large areas …”

Atomic Layer Deposited Ti2O3 Thin Films

“…[36] In addition, some groups have reported the preparation of TiO 2 thin films by the ALD technique. [37][38][39][40][41][42] In this work, we have used this technique to prepare TiO 2 thin films of different thicknesses and reduced them into Ti 2 O 3 films by purging pure hydrogen gas at high temperatures. In this report, preparation, characterization, and electrical properties are discussed.…”

“…By using ALD, thin films of TiO 2 have been recently reported by our group [36] . In addition, some groups have reported the preparation of TiO 2 thin films by the ALD technique [37–42] . In this work, we have used this technique to prepare TiO 2 thin films of different thicknesses and reduced them into Ti 2 O 3 films by purging pure hydrogen gas at high temperatures.…”