Effect of the annealing temperature of the seed layer on the following main layer in atomic-layer-deposited SrTiO${}_3$ thin films

SrTiO${}_3$ (STO) films are grown via atomic layer deposition at 370 °C with a two-step growth method. A 5-nm-thick seed layer is first deposited and annealed via rapid thermal annealing (RTA) at temperatures ranging from 450 to 650 °C, and the main layer is subsequently grown on the annealed seed layer for in situ crystallization. When the RTA temperature is 500 °C or lower, the seed layer remains amorphous, and the main layer is also grown in the amorphous phase. At the 550 °C seed annealing temperature, the STO film is partially crystallized, and at the higher annealing temperature, the STO main layer is fully crystallized. The oxygen diffuses through the vertically aligned grain-boundaries during the crystallized film growth, which induces the oxidation–reduction reaction of the underlying Ru substrate. This reaction causes a higher growth rate in the crystalline phase. The large growth rate difference between the amorphous and crystalline regions induces a severe roughening of the main layer. When RTA is done at 600 °C, the film is mostly crystallized, and the main layer becomes smooth again. Consequently, a 0.52 nm equivalent oxide thickness is achieved with the low leakage current of 2.5 × 10${}^{-8}$ A cm${}^{-2}$ at the 0.8 V applied bias. (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)