La2O3 gate insulators prepared by atomic layer deposition: Optimal growth conditions and MgO/La2O3 stacks for improved metal-oxide-semiconductor characteristics

Abstract

The authors investigated the optimal growth conditions for atomic layer deposition of La2O3 using tris(iso-propylcyclopentadienyl) lanthanum, La(iPrCp)3, and H2O, and identified two necessary conditions for achieving self-limiting growth: A low growth temperature (Ts) of 150 °C–175 °C and an extremely long purging after the H2O feed. Low Ts was also preferable for improving the electrical properties of the metal-oxide-semiconductor devices such as the dielectric constant (k), leakage current, and effective mobility. As for the H2O feed time, a long feed resulted in increased interface-trap density, while a short feed resulted in increased leakage. An H2-plasma treatment inserted after the thin-La2O3 (0.5 nm) film growth reduced the leakage current by 3 orders of magnitude compared to the control sample. An MgO capping on the La2O3 remarkably increased the effective k value; however, it degraded the effective mobility. Transmission electron microscopy indicated that the k-value improvement by the MgO capping is due to suppression of La-silicate formation.