An advanced mechanical system has been developed for the EX-11 electron beam mask writer. In particular, a new XY stage was designed so as to improve CD uniformity and image placement by reduction of vibration and heat generation, and by stabilization of the stage temperature. A direct-drive friction-drive unit and crossed-roller guides enable the stage to obtain low position fluctuation less than +/-1.2 nm over I kHz. The active thermal control system of the XY stage using the thermal control plate whose temperature is controlled within 0.001 degreesC can stabilize that of the top plate of the XY stage. The improved EX-11 is expected to satisfy the requirements for 100 nm C generation lithography.