Band Engineering of Rutile TiO2 by Cobalt Doping in Ru/Rutile-TiO2/Ru Capacitor aiming 40-nm DRAM and Beyond

Ru/Rutile-TiO2/Ru Capacitor aiming 40-nm DRAM and Beyond Osamu Tonomura, Tomoko Sekiguchi, Naomi Inada, Tomoyuki Hamada*, Hiroshi Miki, and Kazuyoshi Torii Hitachi Ltd., Central Research Laboratory, 1-280 HigashiKoigakubo, Kokubunji, Tokyo, Japan, *Hitachi Ltd., Advanced Research Laboratory, Hitachi America Ltd. Phone: +81-42-323-1111, FAX: +81-42-327-7682, Email: osamu.tonomura.mz@hitachi.com Abstract We fabricated Ru/rutile-Co-doped TiO2/Ru capacitor for 40-nm DRAM and beyond having relative permittivity of 90. Doping of Co turned out to increase Schottky barrier leading to decrease in leakage current. Optimum percentage of Co is estimated as 0.3-0.8 % to achieve a sufficiently low leakage-current. Introduction 40 nm-DRAM (Dynamic Random Access Memory) requires capacitor dielectrics with EOT (Equivalent Oxide Thickness) and physical thickness less than 0.5 and 10 nm, respectively (i.e., relative permittivity must be larger than 78), and leakage current less than 10 7 A/cm@1.0 V [1]. A combination of crystallized rutileTiO2 insulator and Ru electrode is one of the promising candidates owing to its large permittivity and large work function, respectively. However, post deposition annealing (PDA) at >800 oC is required to crystallize TiO2 into rutile [2], which is unacceptable for DRAM. [1] It was reported that the rutile-TiO2 can be obtained without high temperature PDA when it is deposited on a rutileRuO2 [3]. In this study, we developed a fabrication process of the rutil-TiO2 directly on Ru electrode without intentional oxidation of Ru. Co doping to TiO2 is also examined to suppress leakage current. Fabrication process Capacitor test structure as shown in Fig. 2 was fabricated. On a SiO2/TiO2 adhesion layer, a 30 nm-Ru is sputtered as a lower electrode. After isolation is formed with SiO2 on Ru, Co-doped TiO2 and Ru upper electrode is sputtered and patterned.