Stoichiometry variation for the atomic layer deposition of Sr_xTi_yO_z from Sr(ⁱPr₃Cp)₂, Ti[N(CH₃)₂]₄ and H₂O

The atomic layer deposition (ALD) of stoichiometric SrTiO₃ as well as layers with either Sr or Ti excess from the commercial precursors Bis(tri-isopropylcyclopentadienyl)-strontium Sr(ⁱPr₃Cp)₂, Tetrakis-(dimethylamido)titanium(IV) Ti[N(CH₃)₂]₄ and H₂O on a commercial ALD system is demonstrated. The influence of the stoichiometry on the optical layer properties was investigated. Spectroscopic ellipsometry shows that all Sr_xTi_yO_z layers are transparent up to the optical gap energy, which amounts to 3.87 eV for stoichiometric SrTiO₃. A direct correlation between the Sr content, optical properties, layer density and the growth per cycle value was determined. X-ray photoelectron spectroscopy after Ar ion cluster sputtering indicates that the layers are free of carbon. After ex situ annealing under atmospheric conditions we observed a change in microstructure from amorphous to polycrystalline starting at 545 °C by atomic force microscopy and grazing incidence X-ray diffraction. Electrical I–V measurements show very small leakage currents confirming the insulating character of the Sr_xTi_yO_z layers. - Highlights: • Sr_xTi_yO_z layers were grown from commercial precursors at a commercial ALD device. • Stoichiometric as well as layers with Sr or Ti excess can be deposited. • At a deposition temperature of 320 °C the layers are free of carbon. • A direct correlation between Sr content, optical properties and GPC was determined. • Ex situ annealing at 600 °C yields completely crystallized SrTiO₃ layers