The electrical degradation of (Ba, Sr)TiO3 [BST] thin films as a function of the film thickness was investigated. BST thin films with various thickness were deposited on Pt/Ti/SiO2/Si substrates by in-situ RF magnetron sputtering. It was found that the electrical properties degraded markedly as the thickness of the films decreased. Electrical properties such as the leakage current and the dielectric constant are closely related to the surface morphology, in particular, the grain size of the films. The existence of an interfacial layer between the BST film and the Pt bottom electrode was confirmed by HRTEM. The interfacial layer appeared to have crystallinity different from both the BST thin film and the Pt bottom electrode which resulted in variation of the interfacial states between BST and Pt. As the thickness of the BST films decreased from 300 nm to 50 nm, the thickness of the interfacial layer increased from 9.5 nm to 11 nm. The dielectric constant of the interfacial layer calculated from its measured overall capacitance and thickness, confirmed by HRTEM, was about 30. This low-dielectric-constant interfacial layer has been shown to affect the electrical degradation of BST thin films with decreasing thickness.
(Ba, Sr)TiO3 (BST) films are deposited on 8-inch wafers by the metal organic chemical vapor deposition
(MOCVD) technique at a temperature as low as 400°C to obtain conformal step coverage and prevent
oxidation of the diffusion barrier of simple stacked capacitors. The problems of low temperature process
(formation of protrusions, titanium deficiency, severe thickness deviation) could be successfully
overcome by proper modification of the CVD system and process conditions. Retrofitting the vaporizer to
obtain flash evaporation of the liquid chemical source and introducing N2O gas as an oxidant were highly
effective for reducing the thickness deviation and titanium deficiency. The Pt/BST/Pt capacitor with BST
films deposited at 400°C and post-annealed at 700°C for 30 min under nitrogen ambient shows excellent
electrical properties (T
o
x∼6.6 Å, J∼1×10-7 A/cm2 @±1 V), which are satisfactory for application to high
density dynamic random access memory (DRAM) capacitors beyond 256 Mbit generation.
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