Characteristics of rf Sputtered Barium Titanate Films on Silicon

Abstract

The physical and electrical properties of barium titanate films approximately 1 μm thick, prepared by rf sputtering onto silicon substrates in both pure argon and 95% argon–5% oxygen glow discharges were investigated. The argon-oxygen mixture was used to minimize oxygen deficiencies in the films resulting from the possible decomposition of the barium titanate in the glow discharge. Sputtering was carried out in a standard diode system with a water-cooled target of ceramic BaTiO3 at power densities of up to 1.6 W/cm2, at a gas pressure of 7–8×10−3 Torr, and in a magnetic field of 20 G. The substrate holder could be heated to about 650°C during deposition. The deposition rate was typically 100 Å/min and was dependent on the sputtering power density and the substrate temperature. The films were deposited on clean n-type silicon wafers of approximately 5 and 0.01 Ω⋅cm resistivity. Some samples were subjected to a post-deposition heat treatment in nitrogen or oxygen ambients at 1000°C. The deposition rate, crystal structure, and refractive index of the films were investigated as a function of deposition temperature and sputtering gas. The electrical characteristics of the films, including the dielectric constant, loss tangent, conductivity, insulator bulk charge, charge storage at the BaTiO3–SiO2 interface, and ferroelectricity were also investigated.