Does Chemistry Really Matter in the Chemical Vapor Deposition of Titanium Dioxide? Precursor and Kinetic Effects on the Microstructure of Polycrystalline Films

Abstract

A side-by-side comparison of the TiO2 deposition kinetics and the corresponding microstructures was studied. The two precursors were titanium(IV) isopropoxide and anhydrous titanium(IV) nitrate, and all depositions were conducted at low pressures (<10-4 Torr) in an ultrahigh vacuum chemical vapor deposition reactor. For both precursors deposition kinetics were qualitatively similar and exhibited three distinct regimes as a function of temperature. At the lowest temperatures, growth was limited by the rate of precursor reaction on the substrate surface. At intermediate temperatures flux-limited growth was obtained, and at the highest temperatures the growth rates decreased with increasing temperatures. The overall behavior was modeled quantitatively for each precursor using a two-step mechanism involving reversible adsorption followed by irreversible reaction. Titanium(IV) nitrate exhibited a lower activation energy of reaction (E r = 98 kJ/mol) which allowed deposition at lower temperatures compared to titanium(IV) isopropoxide (E r = 135 kJ/mol). The film microstructures were examined using transmission and scanning electron microscopy and X-ray diffraction. Comparison of the microstructures of films deposited at similar temperatures revealed significant differences in the reaction rate-limited regime. As the growth rates of the two precursors converged in the flux-limited regime, the respective microstructures became indistinguishable. The importance of precursor surface coverage and diffusion on this effect is described.

Surface reconstructions in molecular beam epitaxy of SrTiO3

“…We first discuss the observed surface reconstructions seen in Figs higher TTIP/Sr at 850 °C compared to 810 °C is consistent with a higher desorption rate for TTIP at higher growth temperatures [15,25].…”

Atomic Layer Deposition, Characterization, and Dielectric Properties of HfO2/SiO2 Nanolaminates and Comparisons with Their Homogeneous Mixtures

“…The deposition chemistry used in the current study is based on previous reports of the successful application of anhydrous metal nitrates for depositing homogeneous and nanolaminate films by CVD and ALD. [7,[9][10][11][12][13][14][15][16][17][18][19] Several reports have described the value of the silica precursor, ( t BuO) 3 SiOH, for depositions of films using ALD. [7,17,[19][20][21] In this article, we demonstrate that alternating layers of hafnia and silica could also be deposited at temperatures as low as 120°C using the procedure developed for ZrO 2 / SiO 2 nanolaminates.…”

Light-Induced CVD of Titanium Dioxide Thin Films I: Kinetics of Deposition

“…The 21 kJ mol ±1 apparent activation energy found for the LICVD process is much lower than the values (between 35 kJ mol ±1 and 135 kJ mol ±1 ) reported for thermal CVD from TTIP. [3,20,21] Additionally, no influence of the laser-induced temperature rise [13] on this Arrhenius term is found. As a matter of fact, a laser-induced temperature rise dependence would mean influences of the fluence, substrate nature, and film thickness, [13] which are not observed.…”