Method and apparatus for forming a variable size electron beam

Abstract

In electron beam apparatus having a souce of electrons and a target area toward which the electrons are directed, electron beam forming means are provided along the path from the source to the target. These forming means include a first beam shaping member having a first spot shaping aperture therein, a second beam shaping member having a second spot shaping aperture therein, and means focusing the image of the first aperture in the plane of the second aperture to thereby form a composite spot shape defined by the image of the first aperture and the second aperture. Further means are provided for focusing the image of the composite spot in the target area. Preferably, the apertures are square shaped. Thus, by varying the position of the superimposed image of the first aperture with respect to the second aperture, a wide variety of rectangular shaped composite spots with different dimensions is obtainable. This permits the exposure of rectilinear patterns, e.g., in photoresists of integrated circuit fabrication, by the electron beam with a minimum of exposure steps and substantially no exposure overlap. The result is greatly increased speed in the total exposure of such rectilinear areas to the electron beam as well as a minimum of the 'blooming effects' produced by exposure overlap.