DIELECTRIC-PROPERTIES AND MICROSTRUCTURE OF THIN BST FILMS

(Ba,Sr)TiO3 (BST) has emerged as the preferred high permittivity thin film material for future generations of high-density DRAM products. Li quid delivery metalorganic chemical vapor deposition (MOCVD) has been used to deposit thin films of BST on Pt/SiO2/Si in a systematic study of thickness and composition effects on microstructure; film orientati on and electrical properties. We have found that smooth, thin films (3 0 nm) with storage densities > 80 fF/mu m(2), low leakage currents (< 10(-7) A/cm(2)), and low dielectric losses (tan delta similar to 0.002 ) can be deposited with high reproducibility when composition is maint ained between 1 - 2 at% excess Ti. Dielectric loss is strongly correla ted to roughness, both of which generally increased with increasing th ickness. For compositions closer to stoichiometry, larger grains forme d at Pt grain boundaries grew faster than the surrounding grains, resu lting in higher variability in dielectric loss.