It is known to utilize direct electron lithography and photolithography during respectively different steps of a process for fabricating a microminiature integrated device. In such a process, an electron beam exposure system is advantageously employed to define some of the more critical features of the device. The other features are defined photolithographically.
For the electron lithographic step(s) of such a hybrid process, highly sensitive electron resists are available. By utilizing these resists, it is economical in some cases to expose even large areas of a resist-coated wafer with an electron beam system. But, in practice, such resists are typically characterized by (1) relatively poor resolution of developed patterns in thick films, (2) relatively poor tolerance to many dry etching processes of practical importance and (3) the disadvantage that the substitution of electron resists for photoresists in a photolithographic fabrication sequence requires modification of a number of the standard photolithographic processing steps other than the exposure step itself. For these reasons in particular, proposals to utilize an electron beam system to complement a photolithographic device fabrication process have not heretofore usually appeared attractive.
Moreover, in such a hybrid fabrication process, it appeared not to be feasible to expose a relatively insensitive photoresist (rather than a sensitive electron resist) with a high-speed electron beam system of the raster scanning type.