Ultrathin (20-100 nm) polymethylmethacrylate (PMMA) films prepared by Langmuir-Blodgett (LB) techniques have been explored as high resolution electron beam resists. A Hitachi S-450 scanning electron microscope has been modified for a high resolution electron beam exposure system. The lithographic properties and exposure conditions of LB PMMA films have been investigated. 0.15 mum lines-and-spaces patterns have been achieved by using the scanning electron microscope as the exposure tool. After etching, the sample has been studied by atomic force microscopy for pinhole measurement. The results demonstrate that the etch resistance of such films is sufficiently good to allow patterning of a 100 nm aluminium film suitable for mask fabrication.