TANTALUM OXIDE THIN-FILMS FOR DIELECTRIC APPLICATIONS BY LOW-PRESSURECHEMICAL-VAPOR-DEPOSITION - PHYSICAL AND ELECTRICAL-PROPERTIES

High quality Ta2O5 films suitable for 64 Mb DRAM use have been deposit ed by low-pressure chemical vapor deposition (LPCVD) from Ta(OC2H5)5 ( tantalum pentaethoxide) and oxygen. The films have been deposited on s ilicon, polysilicon, and SiO2. Thickness reproducibility, across-the-w afer uniformity, and conformality and step-coverage all are excellent. As-deposited films are amorphous with smooth surfaces. Annealed films are polycrystalline, and their surfaces are characterized by 2 nm hig h, 1 mum diam nucleation centers surrounded by circular crystallizatio n fronts. The films must be annealed to get acceptable leakage current s. Leakage currents for annealed 10 to 40 nm Ta2O5 films are independe nt of film thickness and are less-than-or-equal-to 10(-9) A/cm2 at a g ate voltage of 1.5 V Effective dielectric constants decrease with Ta2O 5 film thickness. The smallest observed equivalent SiO2 thickness, t(o x,eff), is 3.5 nm for 7.5 nm Ta2O5/Si. The minimum practical t(ox,eff) for the Ta2O5/Si system is approximately 3 nm. These electrical resul ts are explained by the presence of a thin SiO2 layer at the Ta2O5/Si interface. The SiO2 layer dominates the electrical behavior of thin an nealed Ta2O5 films on Si. Effects of the surface structure and minimum t(ox,eff) on device integration are discussed.