Electron image projector.

摘要

An electron image projector which may be used to project mask patterns with unity magnification onto a semiconductor slice comprises a cathode (C) from which emitted electrons are accelerated by a uniform electric field (E) and focussed by a uniform magnetic field (H) onto a target (T). In known projectors, the accelerating field is produced by a potential difference applied directly between the cathode and the target, which results in the electron trajectories being dependent on the local shape and disposition of the target. To reduce this dependence, a projector embodying the invention comprises an electron-permeable grid (G), the accelerating voltage (V) being applied between the cathode (C) and the grid (G). Suitably, the grid (G) is positioned at the first magnetic focus and the target (T) at the second magnetic focus. A small voltage (δV) much less than the accelerating voltage (V) may be applied between the grid (G) and the target (T) to obtain correct focussing. To prevent the pattern of the grid (G) being reproduced on the target (T), means (MM) are provided to move the grid (G) parallel to the target (T) during an exposure. A detector (ED) of backscattered electrons, positioned adjacent the substantially field- free region between the grid (G) and the target (T), may be used to control the alignment of the projected image with the target (T).