Chemical Vapor Deposition Technology of (Ba,Sr)TiO3 Thin Films for Gbit-Scale Dynamic Random Access Memories

Abstract

AbstractThe current status of (Ba,Sr)TiO3 [BST] capacitor technology using a liquid source chemical vapor deposition (CVD) method is reviewed, focusing on the CVD techniques and the physical, electrical and process-integration-related properties of Ru/BST/Ru capacitors. The use of a new titanium metalorganic (MO) source, titanium bis(tert-butoxy) bis(dipivaloylmethanato) [Ti(tertBuO)2 (DPM)2] dissolved in tetrahydrofuran (THF) turned out to enable highly conformal deposition of BST films with a coverage ratio of ∼ 70 % for a trench with an aspect ratio of ∼ 5. Electrical properties of a 24-nm-thick BST film, deposited on a Pt substrate at a low substrate temperature of 480 °C, were also confirmed to be equivalent SiO2 thickness (teq) of ∼ 0.5 nm and leakage current of ∼ 1 ×10-7 A/cm2 at 1 V. As for the Ru/BST/Ru capacitors, no deteriorations of Ru electrode and BST/Ru interface were observed after 750 °C post-annealing experiment, showing good thermal stability of Ru as a practical electrode material. Although current leak through Ru/BST/Ru capacitors slightly increased after the H2 annealing, such degradation in the leakage properties was restored by post-annealing in N2 ambience. Integrated Ru/BST/Ru capacitors with a 30-nm-thick CVD-BST film were fabricated by 0.5 μm ULSI technology, and low leakage current was confirmed for the stacked capacitors. Regarding the reproducibility of BST deposition by the liquid source CVD method, the deviation ratio of ∼ ± 2.3 % in film thickness was obtained for ∼ 100 successive depositions, thickness uniformity across the wafers was ∼ ± 1.1 %. The above results imply the potential applicability of BST capacitor technology using a liquid source CVD method for Gbit-scale DRAMs.