Role of Interfacial Reaction in Atomic Layer Deposition of TiO2 Thin Films Using Ti(O-iPr)2(tmhd)2 on Ru or RuO2 Substrates

The role of the interfacial reactions in the atomic layer deposition of TiO 2 films was examined using titanium diisopropoxide bis(tetramethylheptadionate) (Ti(O- i Pr) 2 (tmhd) 2 ) as the titanium precursor, and H 2 O or O 3 as the oxygen sources when the films were grown on ruthenium (Ru) or ruthenium dioxide (RuO 2 ) substrate at a growth temperature of 370 °C. Anatase-TiO 2 films with a dielectric constant of 32 were grown on ruthenium substrates when H 2 O was used, whereas rutile-TiO 2 films with a much higher dielectric constant (89) were grown when O 3 was used as the oxygen source. The rutile-TiO 2 film was grown with the aid of an in-situ-formed thin RuO 2 layer on the surface by the strong oxidation power of O 3, which has structural similarity to the rutile-TiO 2 film, as has been reported previously with different precursor and growth temperature [S. K. Kim et al. Appl. Phys. Lett. 2004, 85, 4112]. The initial and steady-state growth rates of the TiO 2 films were strongly dependent on the oxygen source. O 3 induced a substrate-enhanced growth mode at the initial growth step (<25 cycles), whereas H 2 O resulted in a linear growth mode, regardless of the number of cycles, and a lower growth rate at the steady regime, because of its lower reactivity toward tmhd ligands. A substrate-enhanced growth mode was also observed on the RuO 2 substrate, regardless of the oxygen source. Interestingly, RuO 2 was reduced completely to metallic Ru during TiO 2 film growth. Oxygen atoms that come from the reduction of the RuO 2 substrate induced substrate-enhanced growth, and the reduction process was limited kinetically by the growth temperature. Reduction of the RuO 2 substrate occurred at the early stages of TiO 2 film growth. Therefore, it played a key role in determining the phase of the growing TiO 2 films. Reoxidation of the reduced Ru substrate during the O 3 pulse step promoted the formation of rutile TiO 2 .