STOICHIOMETRY MEASUREMENT AND ELECTRIC CHARACTERISTICS OF THIN-FILM TA2O5 INSULATOR FOR ULTRA-LARGE-SCALE INTEGRATION

Elastic recoil detection and Rutherford backscattering were adapted to a stoichiometric study of thin Ta2O5 films deposited on Si substrates by means of the reactive sputtering (SP) and chemical-vapor-deposition (CVD) method. Before annealing the samples it was observed that (i) the atomic ratio of oxygen to tantalum in the SP films agreed with 5/2 within the experimental accuracy and (ii) the CVD films have less oxygen content than the other samples. The specimens were annealed for 30 min under the following three conditions: (a) in dry oxygen ambient at 800-degrees-C; (b) in ozone atmosphere under ultraviolet irradiation (UV ozone) at 300-degrees-C; and (c) two-step treatment of (a) after the (b) process. Each oxidizing process has shown a certain positive effect on the thin CVD samples. Among them, the two-step treatment has proven to be very effective to restore the stoichiometry of 5/2 in the CVD films. Additionally the thickness of contaminant carbon films on the surface of the samples has been reduced by annealing in the oxidizing atmosphere. The relationship between the chemical composition and the electric properties of the samples is discussed.