Vapor etching of ion tracks in fused silica

We have used vapor etching of ion tracks to create high aspect ratio (i.e., length much greater than diameter), isolated cylindrical holes through ∼600-nm-thick films of thermally fused silica on silicon. Samples were exposed to the vapor from water-based liquids with various HF and HF+HCl concentrations. Independent control of the temperatures of the vapor and the samples provided the means to vary separately the etching rates for the tracks and the track-free material. The very rapid etching of the small latent track zone can be explained by preferential capillary condensation. Holes with diameters of ∼24 to ∼80 nm have been documented with length/diameter ratios of up to 22. Although we have restricted this study to thin-film silica, we have evidence that such holes are also formed in bulk fused silica.