Surface-Controlled Deposition of Sc₂O₃ Thin Films by Atomic Layer Epitaxy Using β-Diketonate and Organometallic Precursors

Abstract

Scandium oxide thin film deposition by atomic layer epitaxy was studied at 175−500 °C using Sc(thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and (C5H5)3Sc as scandium precursors. A constant deposition rate of 0.125 Å (cycle)-1 was observed at 335−375 °C on Si(100) and soda lime glass substrates with Sc(thd)3 and O3. The use of H2O2 as an additional oxidizer slightly increased the deposition rate to 0.14 Å (cycle)-1. When (C5H5)3Sc and H2O were used as precursors, the growth rate of Sc2O3 was significantly higher, viz., 0.75 Å (cycle)-1 at 250−350 °C. The effects of growth parameters such as reactant pulsing times were investigated in detail to confirm the surface-controlled growth mechanism. The crystallinity and surface morphology of the films were characterized by XRD and AFM, while ion-beam analysis (time-of-flight elastic recoil detection analysis) was used to determine the stoichiometry and impurity levels. Crystalline thin films with (111) as the dominant orientation were obtained on Si(100) when depositions were carried out at 300 °C or above from Sc(thd)3 and O3 precursors, while films deposited from (C5H5)3Sc and H2O were polycrystalline regardless of the deposition temperature. When films were deposited at 300 °C onto Si(100), the preferred orientation changed from (111) to (100) when the film thickness exceeded 200 nm. Films were stoichiometric when deposited from Sc(thd)3/O3 below 450 °C or from (C5H5)3Sc/H2O at 250 °C or above. When the films were deposited from Sc(thd)3/O3, the carbon content was below 0.1 atom % regardless of the deposition temperature, whereas the hydrogen content decreased to below 0.1 atom % when the deposition temperature was increased to 375 °C. The C and H contents of the films, deposited from (C5H5)3Sc/H2O at 300−400 °C, were around 0.1 and 0.5−0.3 atom %, respectively.