Silicon waveguide on bulk silicon substrate and methods of forming

摘要

Various methods include: forming a first set of trenches in a precursor structure having: a silicon substrate having a crystal direction, the silicon substrate substantially abutted by a first oxide; a silicon germanium (SiGe) layer overlying the silicon substrate; a silicon layer overlying the SiGe layer; a second oxide overlying the silicon layer; and a sacrificial layer overlying the second oxide, wherein the first set of trenches each expose the silicon substrate and internal sidewalls of the first oxide; undercut etching the silicon substrate in a direction perpendicular to the crystal direction of the silicon substrate to form a cavity corresponding with each of the first set of trenches; and partially filling each cavity with a dielectric, leaving an air gap within each cavity connected with an air gap in an adjacent cavity.