Nucleation and growth of thin (Ba,Sr)TiO₃ films in a MOCVD reactor

(Ba_xSr_1-x)TiO₃ thin films were deposited on Pt electrodes in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system. The nucleation behavior and the size of the stable nuclei were investigated by different SPM techniques and by XPS. Characteristic differences were observed between deposition temperatures of 565 °C and 655 °C, i.e. a homogeneous nucleation of small BST grains on the larger Pt grains (100 - 200 nm in-plane size) at low temperatures and a dominating nucleation at the grain boundaries at high temperatures. Further film growth was investigated for nominal film thickness between 5 and 100 nm and details of the grain structure are revealed by HRTEM, e.g., randomly oriented grains (typical in-plane size 10-20 nm) with a high density of twins at 565 °C and (100)-oriented defect free grains of slightly increased size at 655°C. As the electrical properties like permittivity and also leakage current depend on film thickness the final discussions of the electrical properties are based on thickness series and evaluated within the phenomenological dead layer model.