The structure of the organic semiconductor is very sensitive to the electron beam and heat. You cannot fabricate a single nanoribbon OFET using the e-beam lithography or focus ion beam.

http://www.seas.ucla.edu/smrl/PDF%20files%20of%20papers/2010-Large%20Scale%20Pattern.pdf

This depends very much on the organic material. Sergei is right, most organic materials are e-beam sensitive at room temperature, although there are some exceptions. However, this sensitivity is significantly reduced with lowering down temperature. If you have an SEM cryo stage, you could probably do focused electron beam induced deposition (EBID) at lower temperature (temperature should be higher than the chosen precursor's sublimation/evaporation temperature).

Thanks Belova and Sergei