We report on a silicon-based microfabrication process to generate apertures with dimensions of less than 100 nm at the apex of hollow silicon dioxide tips. The fabrication process is self-adjusting and leads to highly reproducible aperture dimensions. It relies substantially on the inhomogeneous thickness distribution and modified etch rate of a silicon dioxide layer thermally grown on structured (001) oriented silicon wafers at relatively low temperatures of about 900-950 degrees C. Process parameters are presented to obtain single or double aperture tips. Once the apertures are fabricated, a further reduction of aperture size below 80 nm is achieved by thin film deposition of, e.g., metal layers or other materials. The possibility of fabricating apertures reliably and reproducibly on large areas, e.g., complete silicon wafers, is emphasized.