Application of electron beam fabrication to multilevel metal structures

The advantages of direct electron beam fabrication and additive metallization in custom wiring of bipolar LSI logic and array circuits include increased interconnection density, mask elimination, and decreased turn around time on new designs. The application of EL–1, a fixed shape beam, results in image fidelity errors which are corrected by exposure compensation and process modification. PMMA type materials are utilized at 10–20 μC/cm2 for both metal pattern definition and interlevel vias. Multiple coating techniques, new developer systems, and developing controls are presented as important features in the patterning process. The importance of separating image and undercut formation in defining and controlling liftoff structure profiles is pointed out in reviewing various approaches.