Electrical, optical, structural and chemical properties of Al2TiO5 films for high-к gate dielectric applications

Abstract

In search of alternate gate dielectrics for electronic applications, aluminum titanate (Al2TiO5) thin films were deposited at room temperature by DC reactive magnetron sputtering and characterized for their structural, chemical, optical and dielectric properties. To realize the potentiality of these films for gate dielectric applications, we investigated the influence of annealing temperature on these properties. From X-ray photoelectron spectroscopic studies, it has been observed in the as-deposited films that the presence of Al3+ and Ti4+ oxidation states which correspond to Al2O3 and TiO2 respectively. After annealing at 400°C in oxygen ambient, the binding energies of Al 2p, Ti 2p and O 1s were shifted by ~1eV and it remains constant with further increase of annealing temperature from 400 to 800°C. This indicates the formation of an intermediate compound of Al2O3 and TiO2. The extracted Al, Ti and O ratio was 2:1:5 which confirms the formation of Al2TiO5. XRD studies indicate that the as-deposited films were amorphous. After annealing at 400°C, a diffraction peak (200) corresponds to aluminum titanate (Al2TiO5) started appearing, and its intensity increases with increase of annealing temperature. Metal-Oxide-Semiconductor (MOS) capacitors were fabricated and characterized to estimate the dielectric properties of the films. The as-deposited films shows high dielectric constant (к=27.0 at 100kHz) and high leakage current density values (J=0.33A/cm2 at 1MV/cm), high oxide traps (5.5×1013cm−2) and high interface state density (1.5×1013cm−2eV−1). After annealing the films show improved dielectric constant and leakage current density values. The films annealed at 600°C in oxygen ambient show better dielectric constant (к=11.2 at 100kHz) and leakage current density values (J=2.23×10−9A/cm2 at 1MV/cm), low oxide traps (1.4×1012cm−2) and low interface state density (7.1×1011cm−2eV−1) compared with the other films. This suggests that the optimum annealing temperature is required to achieve better device properties.