The wet-chemical treatment of silicon wafers is an important production step in photovoltaic and semiconductor industries. Solutions containing hydrofluoric acid, ammonium peroxodisulfate, and hydrochloric acid were investigated as novel acidic, NOx-free etching mixtures for texturization and polishing of monocrystalline silicon wafers. Etching rates as well as generated surface morphologies and properties are discussed in terms of the composition of the etching mixture. The solutions were analyzed with Raman and UV/vis spectroscopy as well as ion chromatography (IC). The silicon surfaces were investigated by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), diffuse reflection infrared spectroscopy (DRIFT), and X-ray photoelectron spectroscopy (XPS). Surprisingly, pyramidal surface structures were found after etching SiC-slurry as well as diamond wire-sawn monocrystalline Si(100) wafers with hydrochloric acid-rich HF-(NH4)2S2O8-HCl mixtures. Acidic etching solutions are generally not known for anisotropic etching. Thus, the HNO3-free mixtures might allow to replace KOH/i-propanol and similar alkaline solutions for texturization of monosilicon wafers at room temperature with less surface contamination. Besides, common HNO3-based etching mixtures may be replaced by the nitrate-free system, leading to significant economic and ecological advantages.
Aqueous acidic ozone (O 3 )-containing solutions are increasingly used for silicon treatment in photovoltaic and semiconductor industries. We studied the behavior of aqueous hydrofluoric acid (HF)-containing solutions (i.e., HF−O 3 , HF−H 2 SO 4 −O 3 , and HF−HCl−O 3 mixtures) toward boron-doped solar-grade (100) silicon wafers. The solubility of O 3 and etching rates at 20 °C were investigated. The mixtures were analyzed for the potential oxidizing species by UV−vis and Raman spectroscopy. Concentrations of O 3 (aq) , O 3 (g) , and Cl 2 (aq) were determined by titrimetric volumetric analysis. F − , Cl − , and SO 4 2− ion contents were determined by ion chromatography. Model experiments were performed to investigate the oxidation of Hterminated silicon surfaces by H 2 O−O 2 , H 2 O−O 3 , H 2 O−H 2 SO 4 −O 3 , and H 2 O−HCl−O 3 mixtures. The oxidation was monitored by diffuse reflection infrared Fourier transformation (DRIFT) spectroscopy. The resulting surfaces were examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). HF−H 2 O−O 3 mixtures show a polishing etching behavior, whereas HF−HCl−H 2 O−O 3 mixtures exhibit slight anisotropic etching. Formation of pyramidal-like morphologies on (100) silicon surfaces was observed. In all cases, cleaned and H-terminated silicon surfaces are obtained. The results were used to draw conclusions about the dissolution mechanism of silicon in the respective solutions. In HF−H 2 O−O 3 mixtures, silicon is dissolved by an O 3(aq) -diffusion-controlled tetravalent etching mechanism. Interestingly, in H 2 SO 4 -rich aqueous HF−H 2 SO 4 −O 3 solutions, only the native oxide is removed, whereas silicon is not attacked and dissolved. In HCl-containing solutions, Cl 2 or Cl 3− are responsible for silicon oxidation. HCl can be considered as a catalyst resulting in a divalent silicon dissolution mechanism similar to the etching in alkaline solutions.
The wet-chemical acidic treatment of silicon wafer surfaces is very important in photovoltaic, microelectronic and further industries. Recent works report on new mixtures for acidic anisotropic etching mixtures based on hydrofluoric acid HF and hydrochloric acid HCl with an added oxidant. The aim of this work was to get an insight into the reactions during the etching process of silicon in the system HF-HCl-Cl 2 . The etching mixtures, gaseous reaction products, as well as the generated silicon surfaces were investigated by 19 F, 29 Si, and 35 Cl NMR, ion chromatography (IC), iodometric titration, FT-IR spectroscopy, diffuse reflectance FT-IR spectroscopy (DRIFT) as well as scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX). A reaction scheme for the anisotropic dissolution of silicon in chlorine containing aqueous HF-solutions is proposed, which involves dissolved Cl 2 as the oxidizing agent, coordination of fluoride/chloride ions and formation of a hydrophilic surface. These steps are similar to the well known alkaline anisotropic etching of silicon.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.