Reactively sputtered tantalum pentoxide thin films for integrated capacitors

The aim of this work was to develop a deposition process for a high-dielectric constant tantalum pentoxide for integrated capacitors. Thin films were deposited reactively on glass wafers using a radio-frequency magnetron sputtering cluster tool at various O₂/Ar flow ratios. By using 2 MeV ⁴He⁺ backscattering spectroscopy and X-ray diffraction, the films obtained showed a stoichiometric orthorhombic β-Ta₂O₅ phase at 20% O₂ in the sputtering gas flow. With low-frequency measurements (f=100 kHz), a 200×200-μm² square metal–insulator–metal (MIM) capacitor with copper electrodes and a 340-nm thick dielectric gave a capacitance density of 0.066 μF/cm², with a quality factor (Q) of 650. The value of the relative permittivity (_r) was approximately 25 determined from MIM capacitors of various sizes. The surface roughness of the 376-nm thick oxide film was found to be small: 0.255 nm. The largest measured capacitor (200×200 μm²) gave reasonable results at low frequencies. When the frequency was increased (100 kHz–20 GHz) only for the smaller capacitors (30×30 μm²) the capacitance remained constant. However, the Q values decreased of the smaller capacitors as a function of frequency. Processed tantalum pentoxide MIM capacitors possessed reasonable electrical properties below 2 GHz and good potential for further improvement.