Polytype Stability, Microstructural Evolution, and Impurities at the Interface of Homoepitaxial 4H-SiC(1120) Thin Films Grown via Hot-Wall Chemical Vapor Deposition.

Abstract

The electronic properties of 4H-SiC make it a leading semiconductor material for high-power applications. Despite advances in SiC crystal growth, devices fabricated in 4H-SiC(0001) continue to be limited by defects like micropipes, dislocations and stacking faults. Investigations performed here on non-basal 4H-SiC have demonstrated micropipe-free, a-plane 4H-SiC films comparable with conventional 4H-SiC(0001). Improved device performance has been achieved for p-i-n rectifiers fabricated in a-plane 4H-SiC.

Hot-wall chemical vapor deposition (CVD) is the most widely used growth process employed to meet the material demands for 4H-SiC-based high-power electronics; however, the suitability of this technique for the growth of thin films (<10 μm) is not well established. A detailed analysis of the epitaxial growth of a-plane 4H-SiC thin films by vertical, hot-wall CVD has been performed in this work. Two growth regimes were identified and termed sublimation growth and precursor growth. In the former, the SiC coating decomposes and results in the in-situ (sublimation) growth of epitaxial SiC films. It is proposed that in-situ layer aids in subsequent thin film growth from reactant gases. Transmission electron microscopy revealed areas without observable defects and an indistinguishable interface between the substrate and sublimation grown layer. Aluminum impurity concentrations to 3E18 per cc. were identified near the interface with the substrate. The influence of these impurities on the cathodoluminescence spectrum of 4H-SiC was studied. A model based on boundary layer theory was developed to explain the origin and the profile of the aluminum impurities. Secondary ion mass spectrometry revealed the SiC coating to be the major source of aluminum impurities. An argon diluent reduced the concentration of aluminum at the interface to 2E17 per cc. Films deposited via precursor growth exhibited specular surfaces. Optical and structural characterization showed the films replicate the polytype of the underlying substrate exactly.

The microstructural evolution of a-plane 4H-SiC and III-nitride films was also investigated. 4H-SiC films showed evidence of step-flow growth in the sublimation-driven regime, while both step-flow and terrace nucleation and growth were observed in the precursor-driven regime. AlN initially grew via the Stranski-Krastanov mode on 4H-SiC , while the Volmer-Weber mode was observed for GaN on AlN.