Processes for making nanoporous SiO2 layers on Si via the irradiation of thermally oxidized silicon wafers with fast ions followed by chemical treatment in a solution or vapor of hydrofluoric acid are presented. It is shown that the density, shape, diameter, and length-to-diameter ratio of channels etched in silicon dioxide can be controlled by varying the regimes of fast ion irradiation or chemical treatment of SiO2/Si structures. Track parameters calculated using the thermal spike model are compared with the chemical etching dat