PROPERTIES OF TANTALUM OXIDE THIN-FILMS GROWN BY ATOMIC LAYER DEPOSITION

Thin tantalum oxide films were deposited using atomic layer deposition from TaCl5 and H2O at temperatures in the range 80-500 degrees C. The films deposited at temperatures below 300 degrees C were predominantly amorphous, whereas those grown at higher temperatures were polycrystalline containing the phases TaO2 and Ta2O5. The oxygen to tantalum mass concentration ratio corresponded to that of TaO2 at all growth temperatures. The optical band gap was close to 4.2 eV for amorphous films and ranged from 3.9 to 4.5 eV for polycrystalline films. The refractive index measured at lambda = 550 nm increased from 1.97 to 2.20 with an increase in growth temperature from 80 to 300 degrees C. The films deposited at 80 degrees C showed low absorption with absorption coefficients of less than 100 cm(-1) in the visible region.