<title>Novel porous silicon formation without external contact</title>

Abstract

Presently two porous silicon formation technologies are published: the anodization into an electro chemical cell and stain etch without external current into a hydrofluoric acid/nitride acid solution. For anodization an external current is necessary in order to achieve porous silicon thicknesses up to 100 micrometers . Stain etch is an electroless process, and the porous layer thickness sis limited to a few micrometers. A novel porous silicon formation technique that combines the advantages of thick layer anodization and electroless stain etch will be shown. A current generated by a galvanic element of silicon and a precision metal on the backside of a silicon wafer in a hydrofluoric acid (HF)/hydrogen peroxide (H2O2)/ethanol electrolyte is utilized in order to generate porous silicon. In this case the silicon operates as anode and the metal as cathode for current generation. This current is similar to the external current needed for anodization. Beside the standard porous silicon etch solution HF and ethanol to oxidizing agent H2O2 is used to support the etch process and to generate a higher etch rate. Etch rate control is given by concentration of etching solution and metalization. Different kinds of metalizations and etching solutions were investigated. This novel technology enables to generate stable porous silicon layers of e.g. 80 micrometers within 10 minutes without an external current. This can be the first efficient way for porous silicon batch processing. Detailed process parameters and characterization will be presented.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.