ELECTRON-BEAM DIRECT WRITING SYSTEM EX-8D EMPLOYING CHARACTER PROJECTION EXPOSURE METHOD

An electron-beam direct writing system which adopts character projection methods in addition to conventional variable-shaped beam methods, has been constructed for 0.15 mum class ultra-large scale integration pattern fabrication. This system is a modified version of our variable-shaped beam machine. The electron optical system adopts a three stage octapole deflector for a 2 mm field and installs an aperture plate exchange mechanism for character projection. The objective lens system was designed so that the beam resolution is 0.04 mum. An optimization study to write a 1G-dynamic random access memory pattern with 0.15 mum design rules showed that a preferable character size and number are 2.5 mum and 48, respectively. The writing speed of this system is designed to be 110 s a chip, using the characters for memory cells as well as peripheral circuits. An advanced beam calibration method has been developed for beam current density and for character size, direction, and position. This method effectively adjusts the current density for each character to be the same on wafers. The beam position is accurately corrected by analyzing the obtained beam intensity distribution.