Metal-assisted chemical etching in HF/Na2S2O8 OR HF/KMnO4 produces porous silicon

A new metal-assisted chemical etching method using Na2S2O8 or KMnO4 as an oxidizing agent was proposed to form a porous silicon layer on a highly resistive p-type silicon. A thin layer of Ag or Pd is deposited on the Si(100) surface prior to immersion in a solution of HF and Na2S2O8 or HF and KMnO4. The properties of porous silicon layer formed by this method as a function of etching time were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX) and reflectance spectrometry. It shows that the surface is porous and the layer thickness is not limited by an instability as observed with electrochemical methods. In addition, reflectance measurements made with a variety of etching conditions show a lowering of the reflectance from 38 to 6%, measured with respect to the bare polished substrate. However, this result can be improved by changing the experimental conditions (concentration, time, temperature, etc.).