Laser-assisted chemical etching for texturing silicon surface

Alkaline etching of silicon surfaces was studied to make anisotropic microstructures. An aqueous solution of potassium hydroxide was used as an etchant. The etching rate of silicon was heavily dependent on crystal orientation and temperature; i.e., the etching rate for the (100) surface was four times larger than that for the (111) surface, and they both increased by ten times as temperature rose from 25 to 60 degrees C. A laser beam was irradiated to a silicon surface to create a temperature distribution that realized selective etching. A pulsed green laser (532 nm) of 5 ns duration was used as a light source to enhance temperature difference between irradiated and nonirradiated portions. By passing through a photomask and an imaging lens system, the laser beam created an optical power distribution on a silicon plate dipped in an etchant. Depending upon the mask pattern, a groove array or a two-dimensional pit array was created on the silicon surface. These pits took a rectangular shape on the silicon (100) plate, while they took a triangular or hexagonal shape on the (111) plate.