Engineering high dielectric constant materials on silicon carbide

The high dielectric constant (high-kappa) materials of hafnium oxide (HfO2) and aluminum oxide (Al2O3) were grown by atomic layer deposition (ALD) and investigated for integration as gate dielectrics in silicon carbide (SiC) power metal-oxide-semiconductor field-effect transistors (MOSFETs).; Smooth HfO2 films were grown on 4H-SiC at temperatures of 200-300°C at a deposition rate of 1-2 A/cycle. A temperature-dependent phase transition from amorphous layer-by-layer growth to polycrystalline three-dimensional island growth was observed by in-situ reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). No interfacial layer formation was observed by in-situ X-ray photoelectron spectroscopy (XPS) and an abrupt interface was confirmed by high-resolution transmission electron microscopy (HRTEM). An asymmetric band alignment at the HfO2/4H-SiC interface was determined by XPS and supported by density functional theory calculations. As a result, a high leakage current density of 10-3 A/cm2 at 3 MV/cm was observed in MOS capacitors.; Al2O3 was studied due to its larger bandgap and potential to form a crystalline oxide film. Epitaxial gamma-Al2O 3 thin films were engineered by post-deposition rapid thermal annealing of amorphous Al2O3 films grown by ALD. An epitaxial relationship of gamma-Al2O3 (111) || 4H-SiC (0001) and gamma-Al2O3 (44¯0) || 4H-SiC (112¯0) was determined by selected area electron diffraction and synchrotron X-ray scattering. An abrupt crystalline interface was observed by HRTEM in films up to 200 A thick. The in-plane alignment between the film and the substrate was nearly complete for gamma-Al2O3 films up to 115 A in thickness, but quickly diminished in thicker films. Mixed amorphous and polycrystalline regions were observed in Al2O3 films thicker than 225 A, and negligible crystallization was observed in films thicker than 500 A. Twinning around the [111] axis was observed in all of the films. Larger barrier heights were determined for the Al2O 3/4H-SiC interface compared to the HfO2/4H-SiC interface and as a result, low leakage current of 10-3 A/cm2 was measured for amorphous Al2O3 films up to an electric field of 8 MV/cm. This state-of-the-art electric field strength is promising for the integration of these materials in SiC power MOSFETs. However, higher leakage current was measured for crystalline Al2O3 films due to conduction along the twin boundaries. Further work is proposed to optimize the quality of the epitaxial Al2O3 films for these applications.