Silicon dissolution regimes from chemical vapour etching: from porous structures to silicon grooving A. Ben Jaballah, M. Saadoun, M. Hajji, H. Ezzaouia, B. Bessaı ¨s * Institut National de Recherche Scientifique et Technique, Laboratoire de Photovoltaique et des Semiconducteurs, BP. 95, 2050 Hammam-Lif, Tunisia Available online 10 July 2004 Abstract A new method of silicon grooving is developed based on chemical vapour etching (CVE) of silicon substrates. The CVE consists of exposing silicon wafers to acid vapours issued from a mixture of HF and HNO 3 . It was found that CVE of silicon results in the formation of Porous Silicon (PS). However, we noticed that, depending on the volume ratio of HF/HNO 3 , PS may transform in a white powder essentially composed of (NH 4 ) 2 SiF 6 . It was shown that PS is a major phase above a volume ratio of 9:1, while the (NH 4 ) 2 SiF 6 phase becomes major at HF/HNO 3 ranging between 2:1 and 4:1. The structural differences between PS and the (NH 4 ) 2 SiF 6 white powder was investigated by Fourier transformation infrared (FTIR) spectroscopy. The formation kinetics of the (NH 4 ) 2 SiF 6 white powder was found to depend on both acid mixture and silicon substrate temperatures. The high solubility of the (NH 4 ) 2 SiF 6 white powder enables us to groove silicon at different depth, with an accuracy of 0.2 mm. This grooving technique could be introduced in microelectronic engineering as well as for buried metal contact in solar cells processing. # 2004 Elsevier B.V. All rights reserved. PACS: 81.05.Rm; 68.37.Hk; 78.30Hv Keywords: Porous silicon; Etching; Grooving 1. Introduction The large development in electronic and photovol- taic systems requires low-cost and efficient technol- ogy. In silicon-based industry, the implementation of electronic devices, buried metal contacts and fiber joints to fiber alignment involve grooves [1,2]. Many techniques were used for silicon grooving [3–5]. These grooves may be obtained by using localized formation of porous silicon together with other phases on silicon substrates. Here, we present a novel groov- ing technology based on chemical vapour etching (CVE) of silicon [6,7]. The CVE technique allows different etch rates and leads to the formation of thick and uniform macro-porous layers when a silicon sub- strate is exposed to an acid vapour flux. The etch mechanism including, the appearance of other phases beside the pore formation processes is still not fully understood. The aim of this work is to study whether it is possible to produce simple and low cost crystalline silicon grooves. Applied Surface Science 238 (2004) 199–203 * Corresponding author. Tel.: þ216 1 430 160; fax: þ216 1 430 934. E-mail address: brahim.bessais@inrst.rnrt.tn (B. Bessaı ¨s). 0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.05.210