X-ray mask fabrication using a subtractive process and a 30 kV acceleration voltage electron beam writer was investigated. The dose margin for delineation of fine resist patterns is increased by reducing the resist thickness. Delineation of 0.1 mu m patterns in a 0.1-mu m-thick resist has approximately the same dose margin as that of 0.2 mu m patterns in a 0.3-mu m-thick resist. Width error in SiO2 patterns used as an etching mask is decreased by reducing the thickness and adding SF6 to CF4 etching gas. Tantalum absorbers can be etched very accurately with electron cyclotron resonance ion stream etching by taking microloading effects and undercutting into account. Using the 0.1-mu m-thick resist, x-ray masks with 0.1 mu m large scale integrated circuit patterns are almost perfectly produced and have a critical dimension accuracy of 13 nm.