Interfacial and electrical properties of radio frequency sputtered ultra-thin TiO2 film for gate oxide applications

Abstract

The electrical responses of ultra-thin TiO2 films in the form of Al/TiO2/Si capacitors prepared by rf sputtering, have been studied in a wide frequency range as a function of post deposition annealing temperature. Thickness, interfacial and surface roughnesses of the heterostructures were extracted by fitting the specular X-ray reflectivity data. The TiO2 film annealed at 800 °C exhibited negligible hysteresis in the capacitance–voltage curve with the lowest interface trap density of 3.18 × 1011 cm−2 eV−1 extracted using Hill-Coleman method. Minimum equivalent oxide thickness (EOT) of 1.67 nm was obtained for the film annealed at annealed at 800 °C with leakage current density of 7.4 × 10−4 A/cm2 at −2 V. Space charge limited current (SCLC) conduction mechanism has been found to be dominant for the film annealed at 400 °C; however for the film annealed at 800 °C, it was found that at lower voltage (<2.5 V) the conduction mechanism is governed by SCLC with a transition to Fowler–Nordheim tunnelling at voltages higher than 2.5 V.