Insights into ALD Growth of Al-Based Dielectric Stack on 4H-SiC

An Al2O3/AlN stack deposited via Atomic Layer Deposition (ALD) methods as a gate insulator for silicon carbide (4H-SiC) has been investigated, focusing on the effects of different Al2O3 deposition processes on the nitride layer. In particular, dielectric stacks, consisting of a 10 nm AlN interface (001)-oriented layer directly grown on a 4H–SiC substrate and in 20 nm of additional amorphous Al2O3 layers were synthesized in sequential deposition runs by thermal ALD (T-ALD) or plasma-enhanced ALD (PEALD) methods. The evolution of the phenomena occurring at the Al2O3/AlN interfaces has been established by in situ ellipsometry measurements. Strong effects of the oxygen plasma because of the O-Al-N bond formation have been clearly observed and corroborated by ex situ structural and electrical characterizations, especially in the case of the plasma-enhanced Al2O3 process. In particular, the Al2O3/AlN bilayer grown by the Al2O3 T-ALD method exhibited good insulating behavior and an 8.7-high dielectric constant was measured. By contrast, the Al2O3/AlN bilayer grown by the Al2O3 PEALD method demonstrated poor insulating properties.