The etching of silicate glasses in aqueous hydrofluoric acid solutions is applied in many technological fields. In this review most of the aspects of the wet chemical etching process of silicate glasses are discussed. The mechanism of the dissolution reaction is governed by the adsorption of the two reactive species: HF and HF
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 and the catalytic action of H+ ions, resulting in the breakage of the siloxane bonds in the silicate network. The etch rate is determined by the composition of the etchant as well as by the glass, although the mechanism of dissolution is not influenced. In the second part of this review, diverse applications of etching glass objects in technology are described. Etching of SiO2 and doped SiO2 thin films, studied extensively for integrated circuit technology, is discussed separately.

Wet chemical etching of silicate glasses in hydrofluoric acid based solutions

When a cleaved optical fibre is immersed in hydrofluoric acid, the compositional variation within the core and the cladding results in the core-region being etched at a faster rate. This paper presents details of the experimental procedures that were used to etch SM 800 optical fibres and the characterization of the micro-cavities using a 3D surface profiler, optical and scanning electron microscopy. Two such acid-etched fibres were fusion spliced to create an intrinsic Fabry–Perot cavity. These strain sensors were surface-mounted on to fibre reinforced composite test specimens and subjected to quasi-static and cyclic loading. The intrinsic fibre Fabry–Perot sensors were interrogated using low-coherence interferometry. The output from the intrinsic Fabry–Perot sensors showed excellent correlation with surface-mounted electrical resistance strain gauges during quasi-static and cyclic loading.

Fabrication of intrinsic fibre Fabry–Perot sensors in silica fibres using hydrofluoric acid etching

The dissolution kinetics of crystalline and amorphous silica were studied as a function of time, temperature, concentration of HF, concentration of HC1, and crystallographic orientation. The results indicate that dissolution is a surface reaction-controlled process. The dissolution rate depends strongly on HF concentration and weakly on HC1 concentration. The dissolution rates depend on crystallographic direction in α-quartz and are slower than for fused silica. The rate-controlling step is thought to be a ligand exchange process at the surface.

William George Palmer

Papers

CCXVI.—The action of aqueous hydrofluoric acid on silica