Effects of Post-Annealing on Dielectric Properties of (Ba, Sr)TiO₃ Thin Films Prepared by Liquid Source Chemical Vapor Deposition

Tsuyoshi HORIKAWA, Junji TANIMURA, Takaaki KAWAHARA, Mikio YAMAMUKA, Masayoshi TARUTANI, Kouichi ONO

Summary :

The post-annealing process has been investigated for (Ba, Sr)TiO₃ [BST] thin films employed as a capacitor dielectric in 1 Gbit dynamic random access memories (DRAMs). The effects of post-annealing on morphology, crystallinity, and dielectric properties were examined for thin film capacitors with BST prepared on Pt electrodes by liquid source chemical vapor deposition (CVD). The direct annealing of BST capacitors caused a roughening in surface morphology of the upper Pt electrodes and BST films. However, the post-annealing of capacitors with a silicon dioxide passivation layer was found to cause little change in surface morphology of Pt and BST, and also no significant deterioration in leakage current. The improvement in crystallinity of BST films through post-annealing was confirmed at a temperature in the range 700-850 by X-ray diffraction (XRD) and transmission electron microscope (TEM). Moreover, the post-annealing experiments for BST films with different compositions showed that the post-annealing greatly increases the dielectric constant of BST films having approximately stoichiometric composition. The leakage and breakdown properties of BST films were also examined, indicating that excess Ti ions result in an increase of the turn-on voltage and the breakdown time. Based on these investigations, the electrical properties of dielectric constant ε 260, equivalent silicon dioxide thickness t_eq 0. 44 nm, and leakage current J_L110^-7 A/cm² at 1. 9 V were successfully obtained for stoichiometric 30-nm-thick BST films post-annealed at 750. Hence, it can be concluded that the post-annealing is a promising technique to enhance the applicability of CVD-deposited BST films with conformal coverage to memory cell capacitors of 1 Gbit DRAMs.

• Publication: IEICE TRANSACTIONS on Electronics Vol.E81-C No.4 pp.497-504
• Publication Date: 1998/04/25
• Type of Manuscript: Special Section PAPER (Special Issue on Advanced Memory Devices Using High-Dielectric-Constant and Ferroelectric Thin Films)

Authors

Tsuyoshi HORIKAWA
Junji TANIMURA
Takaaki KAWAHARA
Mikio YAMAMUKA
Masayoshi TARUTANI
Kouichi ONO

Keyword

chemical vapor deposition,  (Ba,Sr)TiO₃,  annealing,  dielectric constant,  dielectric breakdown