UV-O)3) and dry-O)2): Two-step-annealed chemicalvapor-deposited Ta)2)O)5) films for storagedielectrics of 64-Mb DRAMs

• Published in: IEEE transactions on electron devices Vol. 38; no. 3; pp. 455 - 462
• Main Authors: Shinriki, H, Nakata, M
• Format: Journal Article
• Language: English
• Published: 01-03-1991
• ISSN: 0018-9383
• DOI: 10.1109/16.75185

A capacitor fabrication technique is developed to obtain an extremely thin Ta)2)O)5) film with an effective SiO )2) film thickness of 2.8 nm (equivalent to 12 fF/mum(2 )) for use in a low-power 64-Mb DRAM. A two-step annealing process is used after deposition of the Ta)2)O)5) film by thermal chemical vapor deposition (CVD). The first step is ozone (O)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)3) annealing treatment is proposed. Excited oxygen atoms in the singlet state ((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 )2)O)5) film, resulting in a marked reduction of the film's leakage current. The second step is dry-O)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