IBM’s latest electron-beam mask maker, EL-4, is installed at IBM’s Advanced Mask Facility in Essex Junction, Vermont. The EL-4 system is a 75 kV variable-shaped-beam lithography system designed to produce 1X or NX masks for 0.25 mu m lithography ground rules, extendable to 0.13 mu m. It is currently producing NIST-style x-ray membrane masks with pattern sizes up to 50X50 mm(2) After a brief description of the EL-4 tool and its operating features, the article describes the recently implemented new writing subsystem, provides an overview of the tool software structure, and presents measurement data from masks recently produced on the tool.