A method for the preparation of scanning force microscopy (SFM) tips with spherically shaped tip apexes and known tip radii by exposing commercially available silicon cantilevers to the electron beam of a transmission electron microscope is presented. The spherical shape of the tip apexes was achieved by growth of a contamination layer at the end of the tip using the electron-beam deposition process. Well-defined radii between 7 and 120 nm could be produced. The importance of such tips for quantitative SFM measurements is discussed. Topographical measurements on a special test sample are shown as well as measurements of the frictional force as a function of the loading force as an example for quantitative spectroscopical measurements.