DEPOSITION OF EXTREMELY THIN (BA,SR)TIO3 THIN-FILMS FOR ULTRA-LARGE-SCALE INTEGRATED DYNAMIC RANDOM-ACCESS MEMORY APPLICATION

(Ba,Sr)TiO3 (BST) thin films with thicknesses ranging from 15 to 50 nm are prepared by a rf magnetron sputtering on Pt/SiO2/Si substrates. T he dielectric constants of BST thin films increase with increasing dep osition temperature and thicknesses. The leakage current increases wit h increasing deposition temperature and this prevents the deposition t emperature of the 20 nm thick BST thin film from being increased to a value more than 640 degrees C. The leakage current is also critically dependent upon the postannealing temperature and atmosphere after the top electrode fabrication. The dielectric constant increases with incr easing postannealing temperature which further reduces the SiO2 equiva lent thicknesses of the BST thin films. A 20 nm thick BST thin film de posited at 640 degrees C and postannealed at 750 degrees C under N-2 a tmosphere for 30 min, shows a SiO2 equivalent thickness of 0.24 nm, di electric dissipation factor less than 1%, and leakage current of about 40 nA/cm(2) at -/+ 1.5 V. (C) 1995 American Institute of Physics.