We have investigated the potential use of AlF3thin films (50 nm thick) as negative inorganic resist layers for focused ion beam nanolithography. We demonstrate that 10 nm-wide lines can be fabricated using a Ga+beam of 30 keV incident energy. The resist sensitivity of 1010Ga+/cm is two orders of magnitude lower than for polymethylmethacrylate organic resist. We emphasize that this low sensitivity associated with the exposure mechanism of the resist minimize the influence of the tails of the current distribution within the ion spot. ©1997 American Institute of Physics.