Growth and phase stabilization of HfO2 thin films by ALD using novel precursors

HfO2 thin films were grown at temperatures between 250 and 400 °C by atomic layer deposition using novel cyclopentadienyl-alkylamido precursors, namely CpHf(NMe2)3 and (CpMe)Hf(NMe2)3 (Cp, cyclopentadienyl=C5H5). Ozone was used as the oxygen source. The self-limiting growth mode was verified at 300 °C with a growth rate of 0.7-0.8 Å/cycle, depending on the precursor. Thermal decomposition started to have an effect on the growth mechanism at temperatures near 350 °C. As compared to the widely applied Hf(NEtMe)4 precursor, these novel precursors with higher thermal stability resulted in HfO2 films with lower impurity contents. The carbon and hydrogen contents below 0.5 and 1.0 at.%, respectively, were characterized for films deposited at 300 °C from both novel precursors. The 50-nm-thick HfO2 films deposited at 300 °C or above were crystallized in mixture of monoclinic and cubic or tetragonal phases. Doping with low amounts of yttrium and subsequent annealing of 7-nm-thick film on TiN stabilized the preferred high-permittivity cubic or tetragonal phases, resulting in low capacitance equivalent thickness and leakage current density.