Synthesis of SrTiO3 by crystallization of SrO/TiO2 superlattices prepared by atomic layer deposition

An approach for the preparation of homogenous SrTiO3 (STO) thin films with unprecedented compositional control is presented. Nanolaminates of SrO and TiO2 were deposited at 300 °C by atomic layer deposition on bare silicon, as well as on ruthenium electrodes using metalorganic precursors [Ti(NEtMe)4 (TEMATi),Sr(iPr3Cp)2 (AbsoluteSr)]. Care was taken that the individual sublayers were grown with a number of subcycles well in the steady-state growth regime. This enabled linear composition tuning with the Sr:Ti pulse ratio, which is beneficial for process control. Still, a substrate-specific growth behavior was observed for the individual precursors leading to different cycle ratio/composition dependence for samples grown on Si as compared to Ru substrates. This could be attributed to specific nucleation conditions, which are most pronounced for the initial cycle, but also prevail throughout the film. The as-deposited layers are well separated and the sublayers are amorphous. Subsequent furnace-annealing generated polycrystalline cubic STO films, but also caused a severe distortion of the metal electrode/STO stack, due to interdiffusion. The latter was suppressed by optimized rapid thermal crystallization anneals.