As the dimensions of metal oxide semiconductor field effect transistors (MOSFET) are shrinking, alternative high dielectric constant materials are needed to replace SiO2 (k=3.9) for low energy applications and future electronics. Lanthanide oxides, including La2O3, Sm2O3, Eu2O3, Nd2O3, Er2O3 and Ho2O3, have attracted considerable interest due to their special properties. Among lanthanide oxides, erbium oxide has been studied as an optical material due to its optical properties including high transparency from the ultraviolet to the infrared and high refractive index; some recent studies have reported that erbium oxide thin film can be synthesized as a promising dielectric material on silicon substrates. Compared to other lanthanide metal oxides, such as La2O3 and Sm2O3, erbium oxide is more thermodynamically stable as a result of the small radius of erbium and its negligible interaction/reaction with silicon substrates. In addition, erbium oxide exhibits a relatively high dielectric constant (k = 12-14) which makes it a promising dielectric material for the replacement of SiO2 in future generations of MOSFET.
Earlier studies have shown the advantages of cyclopentadienyl type precursor and ozone in atomic layer deposition (ALD). (CpMe)3Er for Er2O3 deposition using O3 as the oxidizer is the focus of this work. Based on the need for high quality nanostructures based of Er2O3, a study of the ALD of Er2O3 films from such precursor and oxidant is necessary. In this work, tris(methylcyclopentadienyl)erbium and ozone were successfully used for the ALD of carbon-free Er2O3 thin films on Si(100) under a relatively low temperature (170 °C). The effects of temperature on the deposition rate are investigated between 100 and 400 °C, and an ALD temperature window is found. The dependence of Er2O3 film thickness on the ALD cycles is also obtained. The stoichiometric ratio of as deposited Er2O3 was determined by using X-ray photoelectron spectroscopy (XPS). Further, annealing temperatures of 600-1000 °C were required in order to induce interfacial transformations of the Er2O3 thin films deposited on silicon(100) and these interfacial changes are investigated in detail using a variety of highly spatially resolved analytical techniques, including Fourier transform infrared spectroscopy (FTIR) and XPS. The crystal and surface morphology of annealed Er2O3 thin films were studied by using grazing-incidence X-ray diffraction (GIXRD) and an optical surface profiler based on phase-shifting interferometry (PSI) mode.