On The Mechanism of the Anisotropic Dissolution of Silicon in Chlorine Containing Hydrofluoric Acid Solutions

Abstract

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.

Synthesis and Reactivity of an Anti-van’t Hoff/Le Bel Compound with a Planar Tetracoordinate Silicon(II) Atom

“…The 29 Si NMR chemical shifts of δ −33.8 and −233.2 ppm in CD 3 CN relate to the ligand Si nuclei and the central Si(IV) atom, respectively. The latter is in good agreement with the calculated resonance (δ −232.4 ppm, Figure S26) but differs much from that of [SiF 6 ] 2– (δ −188.2 ppm), with six electron-withdrawing F – ligands . The molecular structure established by a single-crystal X-ray diffraction (SC-XRD) analysis revealed a hexacoordinate Si(IV) center adopting a slightly distorted octahedral geometry, with an almost linear I–Si–I arrangement (175.39(7)°) perpendicular to the Si 3 N 2 plane (∑Si = 359.76° within this plane, Figure ).…”

“…The latter is in good agreement with the calculated resonance (δ −232.4 ppm, Figure S26) but differs much from that of [SiF 6 ] 2− (δ −188.2 ppm), with six electron-withdrawing F − ligands. 19 The molecular structure established by a singlecrystal X-ray diffraction (SC-XRD) analysis revealed a hexacoordinate Si(IV) center adopting a slightly distorted octahedral geometry, with an almost linear I−Si−I arrangement (175.39(7)°) perpendicular to the Si 3 N 2 plane (∑Si = 359.76°within this plane, Figure 1). The hypercoordinate Si(IV) center has 3c-4e bonds and thus obeys the octet rule, similar to [SiF 6 ] 2− and a recently reported hexacoordinate organosilane.…”

Morphological and Structural Modifications of Si-Based Nanostructures Synthesized from Metal Silicide Templates in IP6, Acid and Metal Chloride Solutions

“…In addition, a facile solvothermal exfoliation of CaSi 2 to produce partly oxidized ultra-thin Si layers (namely SiOx (0<x<2) of several nanometers thickness was reported in the presence of the ionic liquid butyl-3-methylimidazolium chloride and NH 4 Cl [15]. The oxidation of the Si caused by the presence of Cl in aqueous solution was also reported [16,17], and the extraction of Ca atoms and oxidation of the remaining Si atoms took place in the solutions.…”

Optical Design of Inverted Pyramid Textured PERC Solar Cells

“…There are a variety of structures for surface texturization. − The upright pyramid texture has been widely used in monocrystalline passivated emitter and rear cell (PERC) solar cells, which is commonly obtained by etching (100)-oriented monocrystal silicon wafers in an aqueous alkali such as KOH, NaOH, or TMAH. , The inverted pyramid structure has superior optical properties compared to the upright pyramid structure, which has been suggested by several reports. , With the metal catalysis chemical etching (MCCE) technology or specific chlorine-containing mixtures, a random inverted pyramid structure on the micrometer scale can be fabricated in a low-cost and efficient way. − …”