Preparation of high quality strontium titanate based thin films by ECR plasma sputtering

Strontium titanate based thin films were prepared using a mirror-confinement-type electron-cyclotron-resonance plasma sputtering method. Typically films were deposited Ar/O2 gas mixture with a thickness of approximately 100 nm on Si wafers and Pt/Ti/SiO2/Si multilayer substrates at floating potential and at a temperature below 473 K. Films on Si substrates were found to be amorphous-like both in the preparation of SrTiO3 (STO) films and (Ba, Sr)TiO3 (BST) ones. While on Pt-multilayer substrates STO films could be crystallized well even at as-deposited condition, but BST films were poorly crystallized. As for the post-annealing of these films, 28 GHz millimeter-wave radiation could drastically lower their crystallization temperature. STO films on Si substrates were crystallized at 673 K and BST at 923 K by the conventional method, while by the millimeter-wave method the crystallization temperature of STO films decreased to 573 K and that of BST to 673 K. The millimeter-wave irradiation to STO on Pt-multilayer substrates did not give remarkable contribution to further crystallization, since they were already crystallized well at as-deposited condition. While for BST on Pt-multilayer substrates the temperature again decreased to 673 K by the millimeter-wave irradiation. The dielectric constant of as-deposited STO films on the Pt-multilayer substrates was approximately 70, and it increased drastically to a value of approximately 260, which was comparable with the bulk value, by the millimeter-wave annealing at 573 K.