Fabrication of bonded GeOI substrates with thin Al2O3/SiO2 buried oxide layers

Abstract

Fabrication of bonded Germanium on insulator (GeOI) substrates with thin Al2O3/SiO2 buried oxide layers was demonstrated for the first time. Thin Al2O3 layers grown by an atomic-layer deposition method, which have hydroxyl groups on their surfaces, were inserted to Ge/SiO2 interfaces to strengthen the adhesion between them. The interface bonded in the atmosphere at room temperature without post-anneal processes is flat and exhibits no additional interface. After the wafer bonding, thick GeOI layers were thinned by mechanical polishing, chemical mechanical polishing and O3 water etching. The flatness of the surface is equivalent to that of commercially available Ge substrates. The interface state density (Dit) of the Ge/Al2O3 interface is estimated with low-temperature conductance technique and the Dit of as low as 3.9×1011eV−1cm−2 at the interface is obtained. This value is almost one order of magnitude lower than previously reported Dit of Ge/SiO2 interfaces. These results suggest that negligible negative impact on carrier mobility and sub-threshold characteristics is expected for the back-side interface in the GeOI substrate with thin Al2O3/SiO2 BOX layers.