Electron radiation systems for structure production. Part 1: Physical foundations and experimental results

Microlithograph processes are required to manufacture VLSI semiconductors which are capable of producing extremely fine structures. Reducing electron projection systems were examined for this purpose. On the basis of theoretical considerations concerning the resolution and number of image elements, a reducing electron projector with a scale of 1:4 was developed. The imaging system with corrected compound optics has an optical capability of 37,000 resolvable lines per image field, and a distortion of 0.4 %. The exposure time required for electron lithographic production of 1 micron structures on 8 mm by 8 mm fields is around 2.5 s/sq cm. A highly accurate method of adjustment was developed for the illumination and imaging system. This is essential to reproducible generation of structures by an electron projection system. A new alignment method which yields a registration accuracy of 0.1 micron for multilayer exposures was demonstrated.