Variable development response of resists using electron beam lithography: Methods and applications

In the manufacture of electronic devices for integrated circuits, reducing the number of resist steps is desirable for a variety of reasons. We describe some experiments on a process aimed at reducing the number of resist and registration steps in electron beam lithography. The process involves locally varying the electron dose in an electron sensitive resist (in this case poly[methyl methacrylate]) so that the different levels of exposure can be distinguished by subsequent developing. Reliable results have been achieved with three levels: (i) Strongly exposed (resist removed after short immersion in developer). (ii) Partially exposed or “metastable” (resist removed only after prolonged immersion in developer). (iii) Unexposed. In strongly exposed regions, operations such as etching may take place while using the metastable and unexposed regions to protect the workpiece. Subsequently, the metastable region may be developed for further processing.