Similar to Photolithography, but instead of light the focused electron beam of a scanning electron microscope is used to modify a sensitive layer (resist) which was casted on a silicon wafer for example. A mask is not involved since the impact or dose of the electron beam can be adjust, e.g. Areas to be structured receive a higher dose.

Source

A method of fabricating sub-micron and nanoscale features by exposing electrically sensitive surfaces to an electron beam.

Source