Epitaxial lateral overgrowth of silicon by chemical vapor deposition on ultrathin oxide layers

Abstract

Selective epitaxial growth followed by epitaxial lateral overgrowth (ELO) of silicon through windows in SiO2 in a hot-wall low-pressure chemical vapor deposition system has been used to fabricate silicon-on-insulator (SOI) structures. By careful ex situ and in situ surface cleaning and low-temperature processing, 2.5-μm-thick single-crystal silicon films have been successfully deposited over oxide layers as thin as 35 Å. Dislocation densities in these SOI films over thin oxides are higher than those found in SOI films deposited on thicker oxides. Nucleation of dislocations in the epitaxially grown film is attributed to pinhole expansion in the ultrathin oxide layers during ex situ cleaning, prebake treatment, or ELO processing. An unusual crystallographic defect with attributes of a microtwin-stacking fault complex are also observed in the ELO film appearing over thin oxide layers. A model is proposed to explain this class of defect structure and its formation mechanism.