Effects of Annealing Environment on Interfacial Reactions and Electrical Properties of Ultrathin SrTiO3 on Si

SrTiO3 films were grown by radio-frequency magnetron sputtering and postdeposition annealing (PDA) in N-2, O-2, or NH3 atmospheres. A Sr silicate layer formed at the interface between the SrTiO3 film and Si substrate due to Si diffusion into the films during deposition. This resulted in an inhomogeneous composition of SrTiO3 films along the vertical direction, which was enhanced by PDA. While the thick SrTiO3 film was crystallized after PDA and the permittivity increased (>220), the thin SrTiO3 films remained amorphous even after PDA due to the diffused Si. TiOx in the amorphous SrTiO3 layer was easily nitrided after PDA in an NH3 atmosphere but TiOx in the crystalline SrTiO3 layer was barely nitrided. The electrical properties of the SrTiO3 films were improved by PDA.