Tri-pyramids in silicon epitaxial layers

The external shapes of tri-pyramid defects are summarized and typical shapes, deviations from the typical, and the interactions between tri-pyramids and stacking faults are described. Two basic types of typical tri-pyramids were observed, one with a single peak, and the other with three peaks. The symmetry of the typical tri-pyramids is three-fold. The angle between the apexes of the three pyramids composing the tri-pyramid is 120 °. Each of the pyramids composing the tri-pyramid is a single crystal but with crystallographic orientation different from that of the rest of the layer. The deviations consist of amputated tri-pyramids, bi-pyramids and mono-pyramids, none of which are symmetrical. The layer surface nearest the tri-pyramid is not planar, but distorted. Dash etch was used to reveal stacking faults interacting concentrically with typical tri-pyramids. The dimensions of the tri-pyramid and the stacking fault are proportional to the epitaxial layer thickness. Photographs of interactions among tri-pyramids and stacking faults are obtained by using S.E.M. to obtain high resolution, which reveals finer details in higher magnifications. Traces of SiC or SiO₂ or other foreign materials, together with some basic mechanism, are probably responsible for tri-pyramid formation. They can be prevented by proper treatment of the silicon substrate prior to the layer growth.