Method of using an electron beam

Abstract

When an electron beam is used to effect a process at two adjacent surface areas of a target, such as a semiconductor wafer coated with an electron sensitive resist, various alignment errors can occur, such as where the wafer becomes distorted. The provision of a reference marker, for example a square-etched depression, at the surface of the target between the areas of the target enables the detection of any such distortion. After carrying out the process at one of the areas, an electron beam with a rectangular-shaped spot is directed, in turn, toward the predetermined positions of two mutually transverse sides of the reference marker. In the absence of any alignment error, the beam spot overlies the side in question in order to overlap the marker and the area of the target in the immediate vicinity. Back-scattered electrons can then be detected to give a signal representative of any deviation between the actual position and the predetermined position of the marker so that the electron beam can be correctly aligned when effecting the process of the second of the two areas. For increased accuracy of alignment, a plurality of markers may be provided between the adjacent surface areas.