Precise thickness controlled growth of Al2O3 thin film using ecofriendly direct liquid injection-based low pressure chemical vapor deposition (DLI-LPCVD)

Abstract

Al2O3 thin films are fabricated on Si wafer substrates using direct liquid injection-low pressure chemical vapor deposition (DLI-LPCVD). In DLI-LPCVD, a vaporization chamber supplies vaporized precursors separated from solvents to the deposition chamber, preventing undesired decomposition or premature reactions. DLI-LPCVD is an eco-friendly process that does not require ozone or toxic oxidizing gases; additionally, it is a simple process that eliminates the necessity for precursor injection and purging cycles. Al2O3 thin films are prepared by controlling key process variables, such as substrate temperature and Al(acac)3 solution concentration, which is used as a safe, non-toxic precursor. Their physical and chemical properties are characterized by X-ray reflectivity and grazing incidence X-ray diffraction (GIXRD). Uniform and flat thin films with a surface roughness of 1.9–2.1 nm are fabricated. GIXRD analysis shows that the film fabricated at 550 °C is amorphous. In contrast, a log-scale GIXRD pattern reveals that most of the 800 °C sample is predominantly amorphous, with some cubic γ-Al2O3 present, as confirmed through TEM analysis. Based on XPS results, the ratio of O to Al in thin films fabricated via DLI-LPCVD is 1.43–1.67, close to the stoichiometric ratio of Al2O3. Furthermore, the growth rate controllability of Al2O3 thin film deposition using DLI-LPCVD is 1.9–28 Å/min, depending on the substrate temperature and precursor solution concentration. This study demonstrates the potential of introducing DLI-LPCVD with a vaporization chamber as a new metal oxide thin film deposition process, confirming its ability to control the growth rate precisely. © 2025 Elsevier Ltd and Techna Group S.r.l.