UV-O3 AND DRY-O2 - 2-STEP ANNEALED CHEMICAL VAPOR-DEPOSITED TA2O5 FILMS FOR STORAGE DIELECTRICS OF 64-MB DRAMS

A new capacitor fabrication technique is developed to obtain extremely thin Ta2O5 film with an effective SiO2 film thickness down to 2.8 nm (equivalent to 12fF/mu-m2) for use in low-power 64-Mb DRAM. The key process is two-step annealing after deposition of the Ta2O5 film by thermal chemical vapor deposition (CVD). The first annealing step is ozone (03) annealing with ultraviolet light irradiation, which is the most effective in reducing leakage current. A new model for explaining the effectiveness of UV-O3 annealing treatment is proposed. Excited oxygen atoms in singlet state (1D), which are generated selectively in the ozone gas irradiated by a mercury lamp, repair the oxygen vacancies existing in the as-deposited CVD-Ta2O5 film, resulting in a marked reduction of the film's leakage current. The second annealing step is dry-O2 annealing, which reduces the defect density of initial breakdown. Sufficient capacitance can be obtained while maintaining a low leakage current and sufficient step coverage for 1.5-V supply-voltage 64-Mb DRAM having a high-aspect three-dimensional memory cell.