Thin transparent single-crystal silicon membranes made using a silicon-on-nitride wafer

Abstract

We have produced various transparent silicon membrane applications, such as solar cells, microstructures, sensors and displays by using silicon-on-nitride (SON) wafers. We first tried to make them by using silicon-on-insulator (SOI) wafers and a buried layer Of SiO2 as an etch-stop layer. However, during the wet-etching process, the buried SiO2 layer did not completely block the potassium hydroxide (KOH) etchant. The silicon membrane eventually formed micro-cracks and the membrane broke along the line of micro-cracks. Because the etching selectivity between Si and SiO2 is only 200 : 1 in 30 % KOH at 80 degrees C, the nanometer-order thickness Of SiO2 is insufficient for a suitable etch-stop layer. We have, therefore, developed a wafer that combines a dielectric etch-stop layer with a SOI wafer and that makes it possible to produce transparent silicon membranes of various thicknesses.