Novel porous silicon formation technology using internal current generation

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 precious metal on the backside of a silicon wafer in a hydrofluoric acid (HF)/hydrogen peroxide (H2O2)/ethanol electrolyte is utilised 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. Besides the standard porous silicon etch solution HF (for electrochemical silicon dissolution) and ethanol (to reduce surface tension), an oxidizing agent, H2O2, is used to support the etch process and to generate a higher etch rate. Different kinds of metallization and etching solutions were investigated. nnovative technology enables to generate porous silicon layers of 10 μm without an external current. The porous structure achieved with this new technology is comparable with pores generated with anodization.