Texture Etching of Monocristalline Silicon in Sodium Hypochlorite Solution

Abstract

Alkaline etching has been widely used in silicon technology and applied for different purposes such as damaged layer removal from silicon surfaces, micro-membrane and complex micro-device fabrication for micro-sensor [1] and for micro-optical elements [2]. In the fabrication of solar cells, silicon wafers are generally etched in an anisotropic alkaline solution. It leads to formation of pyramid structure on the surface of the wafer to reduce the reflection loss from the front surface [3]. Different etching solutions have been reported in the literature to texture the silicon surface. In the case of monocristalline silicon, mixed alkaline solutions of sodium hydroxide (NaOH) or potassium hydroxide (KOH) with higher concentrations of isopropyl alcohol (IPA) are the most used solutions to texture the silicon surface [4, 5]. Recently, a strong oxidizing reagent NaOCl has been used successfully by several authors to texture the silicon surface [6, 7]. Moreover, NaOCl is cheaper than other etchants and is also largely used in industry. However, the most important inconvenient of NaOCl is its instability, it decomposes in solution. In this work, the effect of the etching parameters such as solution composition, solution temperature on the silicon surface morphology is studied. The surface of etched samples was characterized by Scanning Electron Microscopy (SEM) and Spectrophotometry. The results clearly show a formation of a homogeneous pyramidal structure and an optimal size of pyramids on the silicon surface. The textured silicon surface exhibits a lower average reflectivity (about 9%) in the main range of solar spectrum (500- 1000nm)