Preparation of Pt/Ru Bilayers and Their Application to the Capacitor of Memory Devices

Abstract

Pt(100 nm)/Ru(80 nm) bilayers were prepared on SiO2/Si substrates by RF magnetron sputtering. Pt films were deposited on Ru layers at temperatures ranging from 300°C to 450°C, while the deposition temperature of Ru films was fixed at 300°C. The Ru layer was found to act as a diffusion barrier as well as a glue layer. With increasing deposition temperature, the grain size of Pt increased. However, the Pt film deposited at 450°C had many voids. In the temperature range from 300°C to 400°C, the sheet resistance of Pt/Ru bilayers linearly decreased with temperature, which is ascribed to increasing crystallinity and grain size. The Pt(450°C)/Ru bilayer, however, showed much higher resistance, caused by voids. Three different capacitors with the structures of Pt/(Ba,Sr)TiO3(BST)/Pt, Pt/BST/RuO2, and Pt/BST/Pt/Ru were fabricated and their properties were characterized. The microstructures of BST films were found to be affected by those of bottom electrodes, and to have an important effect on the electrical properties of the capacitor. The electrical properties, such as dielectric constant and leakage current density, of the capacitor with Pt/Ru bottom electrodes are analogous to those with Pt bottom electrodes and better than those with RuO2 bottom electrodes.