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Carbonaceous masks for selective growth on GaAs substrates were fabricated with high resolution by anodization with an atomic force microscope (AFM). Mask deposition is made by a 15-kV accelerated electron-beam irradiation in a scanning electron microscope. The local anodization of the carbonaceous film under intense electric field is investigated and the main factors for improving resolution and reproducibility are discussed. The “edge effect” of the anodized region, revealed in the electric-field distribution at the tip–water–film interfaces is identified as the main factor responsible for the resolution degradation during patterning. Short forward bias pulse for anodizing the carbonaceous film and the subsequent reverse bias pulse for neutralizing the space charge, locally accumulated during the forward bias, are shown to be effective for the higher pattern resolution and also for deepening the patterning depth. Based on the analysis, a modulated-amplitude pulsed bias mode is proposed and is demonstrated to bring a significant improvement in the resolution and the aspect ratio of patterns made by the anodization. Carbonaceous masks ready for selective area growth of semiconductors alloys were fabricated with the pattern resolution of ∼26 nm, limited by the curvature of AFM cantilever tips. © 2000 American Institute of Physics.