The local nanolithography oxidation technique is implemented by using an atomic force microscope (AFM) for the fabrication of nanoscale patterning structures on a silicon substrate covered whit a thin film of silicon nitride. During the fabrication process, the microscope is operated on air and contact mode utilizing a silicon tip covered whit a hard Cobalt- Chromium coat. The dependence of the oxide growth with the applied voltage was investigated varying this parameter in a range of 1 to 10V to constant scanning speed; the influence of the writing speed in the dimensions of the oxide formed is also analysed varying the speed values between 0.1 to 1μm/s. Is found that the dimensions of lines depend of scanning speed and voltages applied.