(45e) Growth of Epitaxial Γ-Al2O3 Films on 4 H-Silicon Carbide

The development of epitaxial high-k gate dielectrics has the potential to improve the performance of SiC power MOSFETs by improving the interface and enabling operation at a higher electric field. Al₂O₃ (k = 10) is a promising candidate due to its large bandgap and demonstrated stability in several crystalline phases. Al₂O₃ thin films were grown on chemically mechanically polished n-type 4H-SiC (0001) by atomic layer deposition (ALD) at 200C using trimethylaluminum and water vapor. The films were stoichiometric with low carbon incorporation as evaluated by in-situ X-ray photoelectron spectroscopy (XPS). The as-deposited Al₂O₃ films were amorphous as determined by in-situ reflection high-energy electron diffraction (RHEED). Upon annealing in N₂ at 1100C, the film crystallized to the γ-Al₂O₃ phase as observed by RHEED, high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Based on the Fourier transform of the HRTEM image, an epitaxial relationship of γ-Al₂O₃ (111) on 4H-SiC (0001) was observed in which γ-Al₂O₃ (-110) was oriented with 4H-SiC (-12-10). This orientation was further confirmed by XRD analysis in which only the γ-Al₂O₃ (111) and (222) peaks were observed. An abrupt interface of both amorphous and crystalline Al₂O₃ with 4H-SiC was determined by HRTEM. Capacitance-voltage (C-V) and current-voltage (I-V) measurements of 4H-SiC MOS capacitors fabricated with 20 nm Al₂O₃ dielectric films were performed to compare the dielectric constant, fixed charge, density of interface states, and breakdown properties of epitaxial γ-Al₂O₃ films with respect to those of amorphous Al₂O₃ as well as state-of-the-art thermal silicon dioxides.