Thin Transparent Single-Crystal Silicon Membranes MadeUsing a Silicon-on-Nitride Wafer

摘要

We have produced various transparent silicon membrane applications, such as solar cells, mi-crostructures, sensors and displays by using silicon-on-nitride (SON) wafers. We first tried to makethem by using silicon-on-insulator (SOI) wafers and a buried layer of SiO_2 as an etch-stop layer.However, during the wet-etching process, the buried SiO_2 layer did not completely block the potas-sium hydroxide (KOH) etchant. The silicon membrane eventually formed micro-cracks and themembrane broke along the line of micro-cracks. Because the etching selectivity between Si andSiO_2 is only 200 : 1 in 30 % KOH at 80 °C, the nanometer-order thickness of SiO_2 is insufficient fora 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 membranesof various thicknesses.