Resist patterning by scanning probe microscopy is a promising method to create structures in the nanometer range beyond the resolution of conventional electron beam or photo lithography. In conventional resist processing one has to remove either the exposed or unexposed resist in a solvent by an additional step. In this article we demonstrate the possibility of directly writing nano-scaled patterns in a thin amorphous carbon layer, which can be used as an etching mask, by a scanning force microscope. Above a threshold voltage between tip and sample small trenches can be created, whereby the carbon is completely removed from the exposed areas. Evidence is given that the mechanism responsible for the trench formation is a local field-induced oxidation of the carbon layer underneath the tip. ©1997 American Institute of Physics.