Dry etch fabrication of ultra-thin porous silicon membranes

Porous silicon is a well-known material with interesting properties for a wide variety of applications in electronics, photonics, medicine, and informatics. We demonstrate fabrication of porous silicon using a dry etching technique. We demonstrate free standing porous silicon membranes that are only few microns thick. Free standing porous silicon membranes have the ability to behave as a size-selective permeable membrane by allowing specific sized molecules to pass through while retaining others. Here, we employ the XeF2 to develop few micrometers thick suspended porous silicon membranes. The flexibility of XeF2 etching process allows the production of mechanically stable membranes of different thicknesses. By choosing the appropriate etching parameters and conditions, pore size can be tuned to produce porous silicon with optically attractive features and desired optical behaviors. The pore size, porosity and thickness of the various developed ultra-thin free-standing porous silicon membranes were characterized with scanning electron microscopy and optical transmittance measurements. The fabricated free-standing porous membrane has a typical transmission spectrum of regular silicon modulated by Fabry-Perot fringes. Porous silicon thin membranes that combine the properties of a mechanically and chemically stable high surface area matrix with the function of an optical transducer may find many used in biomedical microdevices.