ELECTRON-CYCLOTRON-RESONANCE PLASMA-ENHANCED METALORGANIC CHEMICAL-VAPOR-DEPOSITION OF TANTALUM OXIDE THIN-FILMS ON SILICON NEAR ROOM-TEMPERATURE

Films of tantalum oxide, ranging in thickness from 25 to 2000 nm, mere successfully deposited on silicon by the electron cyclotron resonance plasma-enhanced metalorganic chemical vapor deposition (ECR-MOCVD) process at deposition rates of up to 33 nm/min. The films were produced by decomposition of tantalum pentaethoxide into tantalum oxide in an oxygen ECR microwave plasma. The films mere amorphous (but fully dense) since the temperature of the substrate, which was unheated, was estimated to be 76-120 degrees C. The growth of the tantalum oxide films was accompanied by the formation of an interlayer of silicon dioxide at the silicon interface. The tantalum oxide films were oxygen rich (relative to Ta2O5). The effective relative dielectric constant of these dual-layer dielectrics ranged from epsilon(ef) = 8.5 to 24; this range was explained in terms of a bilayer consisting of a 13-nm-thick silicon dioxide layer of epsilon(sx) = 4, and a tantalum oxide overgrowth of varying thickness having epsilon(tx) approximate to 25. A maximum breakdown strength of the films was 6.9 MV/cm and the leakage current at a field of 1 MV/cm was 3.0 x 10(-8). The breakdown properties mere related to the presence of stray particles on the substrate; these properties are expected to improve considerably if the processing is carried out in a clean-room environment. The silicon dioxide layer is believed to have grown by the diffusion of oxygen through the tantalum oxide overlayer despite the low substrate temperature.