One of the keys for ULSI lithography at a feature size ranging from 180 nm to 150 nm is a stable supply of ultra high precision reticle masks. To meet this demand, we have developed a new electron beam lithography system for reticle masks which offers an exposure accuracy of 20 to 30 nm. The system features a variable shaped beam, 50 kV accelerating voltage, a step-and-repeat stage, nd incorporates new technologies. These include a high resolution-high current density electron optical system, a per-shot focus and shot time correction unit, a high precision beam measurement system utilizing the fitting function method, a single-stage 20 bit electrostatic beam deflection unit and beam-shot smoothing technology. The system achieves a minimum line width of 100 nm or less, a pattern size uniformity of 16 nm (3 sigma) within a field, a field stitching accuracy of plus or minus 19 nm or smaller, and a pattern placement accuracy of plus or minus 29 nm or smaller, resulting in an exposure speed of 3 to 5 times faster than the existing model.