Chemical Vapor Deposition of Ru and RuO2 for Gate Electrode Applications

In this work, Ru and RuO2 films have been investigated for potential applications in emerging CMOS gate electrode and memory capacitor bottom electrode applications. Films were deposited on SiO2 using chemical vapor deposition (CVD) and low power plasma assisted CVD (PACVD) in a 200-mm wafer deposition cluster tool using a metal beta-diketonate precursor [Bis (2,2,6,6-tetramethyl-3,5-heptanedionato) (1,5-cyclooctadiene) ruthenium (II)]. Hydrogen and oxygen were employed as the reactive gases to deposit, respectively, Ru and RuO2, over a wafer temperature range from 320°C to 480°C. The resulting film properties were analyzed using cross-sectional scanning electron microscopy (CS-SEM), four point resistance probe, x-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Both Ru and RuO2 films could be deposited with minimal carbon concentration (∼5 at. %). The purity of the films was also reflected in the as-deposited resistivity of the films, which was as low as 47 μΩ-cm, and was strongly dependent on processing conditions. In order to assess thermal stability, the films were subsequently annealed in forming gas and oxygen ambients for 60 min at 650°C. It was observed that, generally speaking, CVD RuO2 films were stable, with respect to resistivity, in oxidizing ambients, while annealing in a reducing ambient resulted in significant film densification and reduction of the film resistivities to as low as 43 μΩ-cm. Ru films demonstrated good adhesion after anneals in oxidizing, but not in reducing ambients.