Continuously writing electron beam stitched pattern exposure system

Abstract

A large lithographic pattern is written as quickly as possible by writing successive subpatterns in a vector scan mode of operation without any interruption between successive subpatterns. This is made possible by arranging the subpatterns so that they are adjacent to each other and are preferably overlapping and by gradually moving the workpiece with respect to the writing field so as to always keep the subpattern being written within the writing field of the beam. The speed and direction of the workpiece movement (relative to the writing field) is not predetermined for all patterns but is controlled instead by the pattern being written. A sparsely written pattern or portion of a pattern is accompanied by a more rapid table movement than what accompanies a densely written pattern or portion of a pattern. This is made possible by embedding pattern determined workpiece movement commands within the pattern defining data. Through the workpiece movement commands, relative movement between the workpiece and the writing field may be continuously controlled with respect to movement direction, velocity and acceleration. The desired relative position of the workpiece is continuously updated in tiny increments while a laser interferometer control system measures the error between the actual workpiece position and the desired workpiece position and causes the workpiece to track the desired position.