Improved Deposition Process of CVD-(Ba,Sr)TiO 3 on Ru
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IMPROVED DEPOSITION PROCESS OF CVD-(Ba,Sr)TiO3 ON Ru M. Tarutani, T. Sato, M. Yamamuka, T. Kawahara, T. Horikawa, T. Takenaga, Y. Yoneda, T. Kuroiwa, S. Matsuno and T. Shibano Advanced Technology R&D Center, Mitsubishi Electric Corp., Hyogo, JAPAN ABSTRACT (Ba,Sr)TiO3 [BST] films were deposited by the flash vaporization CVD method with a unique liquid delivery system. An inductively coupled plasma mass spectrometry [ICP-MS] analysis revealed the decline of (Ba+Sr)/Ti molar ratio of the initial BST-layer on Ru. By readjusting the flow ratio of liquid sources and using a two-step deposition method, we obtained 30-nm-thick BST films with uniform composition profile, exhibiting good electrical properties. The leakage property, however, was severely deteriorated in BST films less than 24 nm thick. A SEM observation showed the presence of micro-roughness or micro-hillocks in these films, which were confirmed to be caused by Ru oxidation. Therefore, an annealing process of the Ru electrode was added for its planarization, and the CVD process was also improved. As a result, we obtained smooth and finely crystallized ~ 20-nm-thick BST films with good electrical properties of equivalent SiO2 thickness (teq) ~ 0.45 nm and leakage current < 1 x 10-7 A/cm2. We also measured properties of BST films deposited on the 3-D Ru electrode. The results are briefly discussed. INTRODUCTION Metal/insulator/metal [MIM] (Ba,Sr)TiO3 [BST] capacitor has attracted much attention for applications in future high-density memories [1-4]. Ruthenium is promising as the electrode material, because of its feasibility in micromachining via dry etching. The minimum feature size of the future memories is approaching less than 0.15 µm. To meet with such severe design rules, the thickness of BST needs to be limited to less than ~ 30 nm. As the film thickness decreases, it becomes more difficult to minimize leakage current, because the electrical properties of such thin BST films depend particularly on BST/Ru interface characteristics like roughness. In addition, as shown in the following, there is some peculiar property in the initial stage of BST-CVD growth on Ru that influences the BST films severely. Therefore it is necessary to improve the film formation process of CVD-BST films specially optimized for thin BST on Ru, to achieve an MIM-BST capacitor suitable for future high-density memories. In the present paper, we report an improved formation process of CVD-BST on Ru including the control of source flow-ratio, the planarization by Ru annealing and the optimization of CVD process, which enables thin BST films of high-permittivity with low leakage. We also report on properties of BST films deposited on the 3-D Ru electrode. EXPERIMENTAL BST films were deposited by MOCVD method, employing a heated flash-vaporizer and a unique liquid delivery system with a mixture of source liquids and N2 carrier gas [4, 5]. Ba(DPM)2, Sr(DPM)2 and Ti(i-PrO)2(DPM)2 were used as the liquid metal organic sources. THF was used as their solvent. O2 was used as a reactant gas fo
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