Manufacturing of porous silicon; porosity and thickness dependence on electrolyte composition

Abstract

Porous silicon (PS) layers were manufactured by the anodization of silicon (Si) wafers in hydrofluoric acid/ethanol/water (HF/EtOH/H₂O) and hydrofluoric acid/surfactant/water (HF/Decon/H₂O) electrolytes. Physical parameters such as thickness (d) and porosity (p) of the formed PS were determined as the function of concentrations of HF, EtOH, Decon ([HF], [EtOH] and [Decon], respectively). It was found that higher [HF] decreases, while higher [EtOH] increases the porosity and helps to produce both uniform anodization and PS layers. The thickness of the formed PS films were measured by profilometry and prooved to be proportional to [HF] and inversly proportional to [EtOH].

Introduction

Recently, porous silicon (PS) has been a widely studied material owing to its possible applications in optics [1], [2], optoelectronics [3], [4], sensors [5], [6] and quantum electronics [3], [7], [8]. Several detailed papers have already been published concerning the formation [9], [10], and the physical-chemical properties of PS [11]. In general, the papers have not dealt with the dependence of the process and the properties of manufactured PS upon the concentration of the components in the electrolyte. Since the most important parameters of the PS layers are its porosity and thickness, our investigations were focused on how these properties change on varying the composition of the electrolyte. In this paper, the dependence of these parameters on the concentration of the electrolyte is presented.