UV-O/sub 3/ and dry-O/sub 2/: Two-step-annealed chemical vapor-deposited Ta/sub 2/O/sub 5/ films for storage dielectrics of 64-Mb DRAMs

A capacitor fabrication technique is developed to obtain an extremely thin Ta/sub 2/O/sub 5/ film with an effective SiO/sub 2/ film thickness of 2.8 nm (equivalent to 12 fF/ mu m/sup 2/) for use in a low-power 64-Mb DRAM. A two-step annealing process is used after deposition of the Ta/sub 2/O/sub 5/ film by thermal chemical vapor deposition (CVD). The first step is ozone (O/sub 3/) annealing with ultraviolet light irradiation, which is the most effective means of reducing leakage current. A model for explaining the effectiveness of the UV-O/sub 3/ annealing treatment is proposed. Excited oxygen atoms in the singlet state (/sup 1/D), which are generated selectively in the ozone gas irradiated by a mercury lamp, repair the oxygen vacancies existing in the as-deposited CVD-Ta/sub 2/O/sub 5/ film, resulting in a marked reduction of the film's leakage current. The second step is dry-O/sub 2/ 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 a 1.5-V supply-voltage 64-Mb DRAM having a high-aspect three-dimensional memory cell.<
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