Atomic-layer deposition of TiO2 thin films with a thermally stable (CpMe5)Ti(OMe)3 precursor

Highlights: • An ALD process of TiO₂ films from (CpMe₅)Ti(OMe)₃ and O₃ is examined. • The high thermal stability of (CpMe₅)Ti(OMe)₃ enables the ALD window up to a high temperature of 345 °C. • Dense and high-purity TiO₂ films were grown at higher temperatures of >300 °C. • The morphology with patterns spreading radially from multiple points eventually disappears at high temperatures of >300 °C. Atomic layer deposition (ALD) of TiO₂ films from (CpMe₅)Ti(OMe)₃ as precursor and O₃ as co-reactant was examined. The high thermal stability of (CpMe₅)Ti(OMe)₃ enabled ALD reaction up to a high temperature of 345 °C. A wide temperature window from 182 to 345 °C was achieved in the ALD process, and the growth per cycle increased with increasing the temperature from 0.025 to 0.06 nm/cycle in the ALD window. The impurity content of the films decreased with increasing growth temperature. Above 291 °C, the carbon content in the films decreased to the level in a single crystalline Si substrate. The morphology with patterns spreading radially from the multiple points developed above 236 °C, and the size of the grains decreased as the growth temperature increased. Eventually, a uniform morphology with fine grains was obtained at temperatures > 300 °C. The films grown at the high temperatures exhibited superior dielectric properties. Other common metalorganic precursors of Ti usually restrict the use of high-temperature ALD because they are thermally unstable and decompose below 300 °C. Therefore, (CpMe₅)Ti(OMe)₃ is favorable for forming dense and high-purity TiO₂ films by ALD.