A comparative study on lanthanide oxide thin films grown by atomic layer deposition

Lanthanide oxide (Ln=Nd, Sm, Eu, Gd, Dy, Ho, Er and Tm) thin films were grown onto silicon (100) substrates by atomic layer deposition (ALD) using volatile β-diketonate-type Ln(thd)3 (thd=2,2,6,6-tetramethyl-3,5-heptanedione) compounds and ozone as precursors. The depositions were carried out at approximately 300 °C under a reduced pressure of 2-3 mbar. X-ray diffraction studies showed all Ln2O3 films to be cubic (C-type) and polycrystalline. Nd2O3 was observed to contain hexagonal phase as well. Compositional studies by time-of-flight elastic recoil detection analysis (TOF-ERDA) revealed the films to be nearly stoichiometric having carbon, fluorine and hydrogen as impurities. According to the infrared spectroscopy measurements, the carbon contamination in the films was mainly caused by a carbonate-type impurity. Electrical characterization showed that thin films were resistive having relative permittivities between 8.4 and 11.1. Leakage current densities through ca. 50 nm thick Ln2O3 were in the order of 10−9-10−7 A/cm2 and breakdown field strengths were in the range of 0.4-2.1 MV/cm.