Impact of Growth Conditions on the Phase Selectivity and Epitaxial Quality of TiO2 Films Grown by the Plasma-Assisted Atomic Layer Deposition
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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Plasma-enhanced atomic layer deposition PE-ALD is a promising method to grow conformal, epitaxial films at low temperatures 300 degrees C. In this study, PE-ALD was used to deposit high-quality, epitaxial anatase and rutile TiO2 thin films on sapphire substrates with various orientations c-, m-, and a-Al2O3. For all substrate orientations, the influence of ALD growth temperature and plasma gas chemistry on the film morphology, phase, and crystallinity was investigated. On c-Al2O3, using a mixed Ar-O-2 plasma, the phase selectivity between anatase and rutile TiO2 could be achieved by simply controlling the growth temperature from 150 to 350 degrees C. By using a pure O-2 plasma, single-phase rutile TiO2 was grown independent of temperature or substrate orientation. Additionally, using a pure O-2 plasma resulted in higher crystalline quality films as growth temperatures were reduced, resulting in single-phase crystalline films at 150 degrees C. Although high-quality rutile films were attained on c- and m-Al2O3, only low-quality crystalline rutile films were produced on a-Al2O3. These results demonstrate the benefits of a PE-ALD approach toward depositing epitaxial TiO2 under low-temperature conditions that is of high quality, phase and strain selective.