High angle close to 90° tilt Si boundary created by direct wafer bonding (DWB) using SmartCut® technology is studied in this work. Experimental identification of defects and morphologies at the interface is realized using conventional transmission electron microscopy (TEM) and geometric phase analysis (GPA) of high-resolution TEM images. Atom reconstruction of the interface along the direction is carried out within the frame of the O-lattice theory. We demonstrate that to preserve covalent bonding across the interface it should consist of facets intersected by a maximum of six planes with three 90° Shockley dislocations per facet. For a long enough interface the formation of Frank dislocations is predicted with a period equal 6 times that of Shockley dislocations. Long range undulations of the interface are shown to be related directly to a deviation from exact 90° tilt of the layer with respect to the substrate.