A Modified SEM Type EB Direct Writing System and Its Application on MOS LSI Fabrication

Abstract

A modified SEM type electron beam exposure machine adopts an auto‐registration function and it is converted to a direct writing purpose system. One‐chip‐one field and chip‐by‐chip registration scheme is adopted to increase the field size and to eliminate stage‐related problems, such as laser interferometric control complexity and stage movement slowness. 2 μm rule 64 k ROM, shrunk to 4/10 from the original design, is used as a device for testing the developed EB system capability. 0.8 μm high, 2 μm wide, L‐shaped step made from bulk Si is used as registration marks and ±0.1 μm of 2 level overlay accuracy is achieved. Although no special optimization or device design modification is done on the shrinkage, the device fabricated by all EB direct writings and dry etching process shows no noticeable difference in electric functions from one made by photolithographic (DSW) processes. The system is stable without intensive maintenance jobs and overlay accuracy through the process (7 exposing levels) is better than ±0.25 μm, although the registration mark structure is changed by the fabrication processes. It becomes clear that this kind of direct writing machine is very useful for research of EB lithography and the LSI development.