Metal-Assisted Chemical Etching of Multicrystalline Silicon in HF/ Na_2S_2O_8 Produces Porous Silicon

摘要

A new metal-assisted chemical etching method using Na_2S_2O_8 as an oxidant is proposed to form a porous layer on a multicrystalline silicon (mc-Si). This method does not need an external bias and enables formation of uniform porous silicon layers, more rapidly than the conventional stain etching method. A thin layer of Pd is deposited on the mc-Si surface prior to immersion in a solution of HF and Na_2S_2O_8. The characterisations of etched layer formed by this method as a function of etching time were investigated by scanning electron microscopy, X-ray diffraction (XRD), Energy-dispersive X-ray (EDX) and reflectance spectroscopy. It shows that the surface is porous and the etching is independent of grain orientation. In addition, reflectance measurements made with a variety of etching conditions show a lowering of the reflectance from 25 percent to 6 percent measured with respect to the bare as-cut substrate. However, this result can be improved by changing the experimental conditions (concentration, time, temperature, ...).