Edge effect in the oxidation of three-dimensional nano-structured silicon

Understanding and controlling the oxidation of 3D nano-structured Si is important for the three-dimensional (3D) nano-structured vertical metal–oxide–semiconductor (MOS) field-effect transistor. The retarded oxidation of Si in a corner (edge) has been widely considered since the 1980s to be due to the compressive stress from oxide and/or the slow diffusion of the oxidant in the oxide caused by compressive stress, although some problems remain unresolved. In the current work, a sharp angle in a simultaneously oxidized concave-structured adjacent two-dimensional planar surface was observed for the first time by using transmission electron microscope, for which the traditional consideration is difficult to interpret. We also found that the oxidation of Si near the edge is delayed (edge effect) irrespective of whether the edge is non-oxidized Si ₃ N ₄ or a simultaneously oxidized convex- or concave-structured adjacent two-dimensional planar surface, widely exists in different Si planar surface of the observed 3D nano-structures (pillar, fin, and terrace) independent of grain orientation. We further developed a model for the formation of the edge effect and discussed its mechanism. The edge effect completely explains the residual Si and formed SiO ₂ in all Si nano-structures and also contributes in intrinsically understanding and precisely controlling the oxidation of 3D nano-structured Si for future device fabrications.