Variation in the density, optical polarizabilities, and crystallinity of TiO2 thin films deposited via atomic layer deposition from 38 to 150 °C using the titanium tetrachloride-water reaction

Abstract

Refractive index, density, and optical polarizabilities as a function of atomic layer deposition (ALD) growth temperature for titanium dioxide (TiO2) thin films are reported for the first time between 38 and 150 °C using the titanium tetrachloride-water reaction. Consistent with prior reports, Raman spectroscopy and x-ray diffraction indicate that the films are amorphous below 150 °C and form the crystalline anatase phase at deposition temperatures at or above 150 °C. Despite this change in atomic structure, mass densities of the TiO2 films are found to increase smoothly between 38 and 125 °C (3.25–3.68 g cm−3), as measured by both x-ray reflectometry (XRR) and optical ellipsometry. Molecular polarizabilities were calculated from the XRR mass densities, and ellipsometric refractive indices and were found to vary from 5.26–5.83 × 10−24 cm−3, which is consistent with prior reports of chemical vapor deposition of amorphous TiO2 thin films. Here, the authors demonstrate that the greater precision of ALD provides better control over the atomic structure and molecular polarizability of amorphous TiO2 thin films than other growth approaches, providing new opportunities for precisely studying the structure of amorphous oxides.