Effect of SiO2 buffer layers on the structure of SrTiO3 films grown on silicon by pulsed laser deposition

Thin films of SrTiO3 were grown by pulsed laser deposition on Si and SiO2/Si at 35 and 650 degrees C in a 50 mTorr oxygen discharge (300 V). The effect of introducing a SiO2 buffer layer between the Si substrate and the complex oxide on the crystallinity and microstructure of the SrTiO3 films was investigated at both deposition temperatures. All films grown at 35 degrees C were amorphous. Surface morphology examination by scanning electron microscopy (SEM) showed that these films were continuous and homogeneous when grown on Si, but were porous and had low-density noninterconnecting lines when grown on SiO2/Si. Films prepared at 650 degrees C were polycrystalline and their x-ray-diffraction patterns exhibited peaks corresponding to the (001), (110), (111), and (002) reflections of the SrTiO3 cubic phase (a=3.904 Angstrom). The films deposited on SiO2/Si were found to grow with a high degree of preferred orientation along the (110) direction. SEM studies on the surface morphology of the films grown at high temperature showed the presence of a ''rosette'' structure. The mean size of the rosettes was similar to 80 nm in 40-nm-thick films grown on Si and similar to 100 nm in films of similar thickness grown on SiO2/Si. Additional atomic force microscopy studies on the topography of these samples indicated that the rosettes were constituted by similar to 35-nm-diam grains. Typical peak-to-valley surface roughness of these films was 0.5-2 nm. (C) 1996 American Institute of Physics.