High-accuracy alignment of the grating pattern along silicon 〈1 1 2〉 directions using a short rectangular array

Abstract

A method for the accurate alignment of the grating pattern along silicon 〈1 1 2〉 directions is developed. A short rectangular array is fabricated as an alignment pattern in silicon wafer through quick pre-anisotropic wet etching. The short rectangles can locate the {1 1 1} planes with zero error without the need to determine the crystal directions manually. The grating pattern is aligned along 〈1 1 2〉 directions by using the diffraction characteristic of the short rectangular array without a superfluous process or equipment. The alignment pattern occupies an area of less than 4 mm2 and can be fabricated through one-time wet etching in any location on the silicon wafer. The alignment error of this method is up to 0.013°. The method is used to fabricate a silicon grating with a period of 220 nm and a groove depth of 1.8 µm. The sidewalls of the grating are atomically smooth {1 1 1} planes with an RMS roughness of 0.162 nm.