The Etching Mechanisms of SiO2 in Hydrofluoric Acid

Abstract

The different equilibria in HF and HF/HCI solutions are examined and the etching reaction of SiQ is investigated as a function of the different species present in the HF solution. A new model for the etching mechanism of SiO~ is developed based on the existence of the dimer of HF, (HF)~.The dissolution of SiQ in HF solutions is a fundamental step in the fabrication of integrated circuits. Mat and Looney ~ have studied the etch rate of SiO2 in HF solutions as a function of the concentration, the temperature, the oxide growth process, and the stirring of the solution. The overall chemical reaction involved is normally understood as

Initial stages of porous silicon formation: An in‐situ investigation of the electronic properties and surface morphology

“…8 shows that, compared to the 0.1 M NH 4 F (pH 4) solution, about a one order of magnitude higher charge flow is necessary to reach the oxide formation regime in the 1 M solution. This behavior can be explained by a higher etching rate of the Si oxide in the higher concentrated solutions [63,[65][66][67][68].…”

Solubility and dissolution rate of silica in acid fluoride solutions

“…The initial adsorption of the HF molecules on the silica surface results in a weakening of the surface bonds by the association of the HF protons with the adjacent lattice (terminal) oxygens. Verhaverbeke et al (1994) suggest that the etching mechanism of silica in hydrofluoric acid involves the dimers H 2 F 2 and HF 2 À . They propose that HF 2 À primarily controls the etching at very low concentrations and with increasing total fluoride concentration, the contribution of HF 2 À decreases accompanied with a corresponding increase in the contribution of H 2 F 2 .…”

“…In our subsequent discussions we will only consider the species HF, F À and HF 2 À . Verhaverbeke et al (1994) suggested that for understanding the etching process of silica by HF, the concentration range up to 1 m is the most important. HF, F À and HF 2 À are the most important species in the pH range from 0 to 6, at a F À < 1 (Fig.…”

“…Dissolution rates in pure water predicted by Rimstidt and Barnes (1980) are shown by the tic marks on the right axis. Kikuyama et al, 1992;Kline and Fogler, 1981;Knotter, 2000;Osseo-Asare, 1996;Prokopowicz-Prigogine, 1989;Proksche et al, 1992;Spierings, 1993;Spierings and van Dijk, 1987;Verhaverbeke et al, 1994) or ab initio quantum mechanics models (Hoshino and Nishioka, 1999;Kang and Musgrave, 2002;Trucks et al, 1990).…”

“…(7). Verhaverbeke et al (1994) argue that to model the etching mechanism using HF requires the simultaneous participation of four HF molecules in an elementary reaction and that is not probable. Hence, the mechanism for 22) and considering solution speciation.…”