Titanium diboride thin films by low-temperature chemical vapor deposition from the single source precursor Ti(BH ₄) ₃(1,2- dimethoxyethane)

Titanium diboride is a technologically important refractory conductor with a melting point of 3220 °C, a high electrical conductivity, and good wear and corrosion resistance. Thin films of TiB ₂ have been obtained at temperatures as low as 170°C by thermal chemical vapor deposition from the halogen-free single-source precursor Ti(BH ₄) ₃(CH ₃OCH ₂CH ₂OCH ₃). Films deposited at temperatures below 200°C are near stoichiometric, free of impurities, and amorphous as judged by X-ray diffraction. These films exhibit dense nucleation, including on SiO ₂ substrates, and have root-mean-square roughness, as measured by atomic force microscopy, of less than 1 nm for films 5-60 nm thick. At growth temperatures between 200 and 600°C, the films are still amorphous but contain 12-15 atomic % oxygen and 15-20 atomic % carbon; these impurities are incorporated at the expense of boron. For growth at 800°C and above, the films are crystalline, stoichiometric, and free of impurities. These high-temperature films are oriented in a preferred fashion with respect to the substrate: on Si(100) the films have a (101) orientation when grown at 800°C but a (001) orientation when the films are grown at 900°C. An amorphous TiB ₂ film, grown at 175°C to a thickness of 7 nm, performs well as a diffusion barrier: no Cu diffuses across the TiB2 after thermal annealing at 600°C for 30 min.