Characterization of stain etched p-type silicon in aqueous HF solutions containing HNO3 or KMnO4

Stain etching of p-type silicon in hydrofluoric acid solutions containing nitric acid or potassium permanganate as an oxidizing agent has been examined. The effects of etching time, oxidizing agent and HF concentrations on the electrochemical behavior of etched silicon surfaces have been investigated by electrochemical impedance spectroscopy (EIS). An electrical equivalent circuit was used for fitting the impedance data. The morphology and the chemical composition of the etched Si surface were studied using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques, respectively. A porous silicon layer was formed on Si etched in HF solutions containing HNO3, while etching in HF solutions containing KMnO4 led to the formation of a porous layer and simultaneous deposition of K2SiF6 inside the pores. The thickness of K2SiF6 layer increases with increasing the KMnO4 concentration and decreases as the concentration of HF increases.