Tantalum Oxide Thin Films Sputter-Deposited by Oxygen Gas Pulsing

Tantalum oxide thin films are deposited by DC reactive magnetron sputtering from a tantalum metallic target and argon + oxygen. The oxygen gas is pulsed during the deposition with a constant pulsing period T = 10 s, whereas the introduction time of the reactive gas, namely the t(ON) injection time, is systematically changed from 0 to 100% of T. Therefore, composition of as-deposited TaOx films is continuously changed from pure metallic tantalum to the over-stoichiometric Ta2O5 material. Films adopt the body-centered cubic structure (metallic Ta) for the lowest t(ON) injection time values (oxygen stoichiometry x < 1.0) and become amorphous for the longest ones. It is shown that the t(ON) injection time is a key parameter to deposit either homogeneous tantalum oxides, or periodic Ta/TaOx multilayers with alternations close to 3 nm. Optical transmittance in the visible region of the film/glass substrate system and electrical conductivity vs. temperature both exhibit a gradual evolution from metallic (sigma(300K) = 8.17 x 10(5) S m(-1) with an opaque behavior) to semiconducting (sigma(300K) = 1.97 x 10(3) S m(-1) with a semi-transparent transmittance) and finally to dielectric properties (sigma(300K) < 10(-5) S m(-1) for interferential films) as a function of the oxygen concentration in the films.