Morphological and Optical Properties of Stain Etched Silicon in Vanadium Oxide (V2O5) / Hydrofluoric Acid (HF) Solution

In the current semiconductor industry, silicon (Si) nanostructures represent the basic material for the conception of several devices in the field of nanoelectronics,  optoelectronics, energy conversion, energy storage, and also (bio) chemical sensors.Various methods have been developed to fabricate Si nanostructures such as reactive ion etching (RIE), electrochemical etching, metal-assisted etching or stain etching. This last one is an electroless method to form porous silicon (PSi) in a mixture based on hydrofluoric acid (HF) and an oxidant.

In this work we report the fabrication of ordered macroporous silicion structures by chemical etching of silicon in vanadium oxide (V₂O₅) and hydrofluoric acid (HF) solution. The effects of the different etching parameters, including the etching time and the presence of metal catalyst film deposition (Pd, Ag), on the morphologies and the optical properties of the etched Si surfaces were studied.  Scanning Electron Microscopy (SEM) was carried out to explore the morphologies of the as etched surfaces with and without the presence of catalyst. The obtained structures were characterized by Fourier Transform Infrared Spectroscopy (FTIR). A spectrophotometer UV-Vis-NIR was used to study the reflectance of the obtained structures.

It has been found that the morphology depends on  the etching time and on the presence and the type of the catalyst. The results show that the attack of the silicon surface coated with Palladium or Silver deposit begins by creating circular pores. Moreover the pore diameter can be easily varied by changing the etching parameters such as the concentration and the etching time. In addition, long etching time leads to the formation of porous pyramidal structures at the bottom of the pore silicon. Finally,the presence of metal catalyst (Pd or Ag) does not only accelerate the etch rate but also creates pyramidal structures within the macropores.

A reflectance around 1,78% for the Ag/Si structures and about 4% for Pd/Si structures was obtained after 60 min etching. The surface hydrophobicity was also studied for the obtained structures and we observe a contact angle of 145°.