Paper TF-ThP2
(Dual) Ion Beam Deposition of Tantalum Pentoxide Thin Film at Room Temperature

Thursday, October 18, 2007, 5:30 pm, Room 4C

Tantalum pentoxide is a material with outstanding optical (high refractive index, high transparency) and electrical properties (high dielectric constant), rendering it a promising candidate for applications in rapidly developing fields such as optics, microelectronics, and sensorics. Many modern application are based on plastic substrates such as PMMA, which in turn requires deposition at low or even room temperature. To meet this end, the deposition of Ta₂O₅ films by means of (dual) ion beam deposition at room temperature on Si, glass and plastic substrates has been investigated. A tantalum target was sputtered by Ar ions from a Kaufman source in the presence of oxygen, while the growing film was simultaneously bombarded with Ar or O ions from a plasma beam source. Films have been characterized with respect to their morphology, thickness, composition, bonding structure, and optical properties by techniques such as atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), variable angle spectroscopic ellipsometry (VASE) and UV-VIS spectroscopy. In a first step, the influence of the oxygen partial pressure on the properties of single ion beam sputtering was investigated. It turned out that the oxygen content in the films increased with the oxygen partial pressure until saturation at the stoichiometric value is reached. These films are extremely smooth (rms roughness < 0.15 nm), possess refractive indices of 2.1 or even higher and extinction coefficients lower than the detection limit of the ellipsometer (ca. 10^-3). In a second step, the influence of a densification of the growing films by simultaneous bombardment with either oxygen or argon ions was studied. The parameters investigated were the ion current density and the ion energy. A major aim of this study was to establish a correlation of the basic film properties, especially the bonding environment as revealed by XPS and FTIR, one the one hand, and the optical properties, on the other hand.