Automatically aligned electron beam lithography on the nanometre scale

A scanning electron microscope SEM.has been modified to enable it to be used for electron beam lithography. This involved modifications to the electron optics and sample stage of the SEM, as well as adding an image correlation system and pattern generator to provide the alignment and lithography functions. The instrument has been used for direct-write electron beam lithography to fabricate devices with dimensions on the nanometre scale. The standard SEM stage has been motorized and is used to move to each device. The location of each device is found by using a hierarchical image correlation technique and electron beam deflection system to achieve a device alignment accuracy of 80 nm. The main application is to write the gate electrodes in gallium arsenide high electron mobility transistors HEMTs.. A variety of HEMT designs have been written with exposed linewidths of 130 nm. The instrument has also been used to write large arrays of closely spaced electrodes as part of a semiconductor detector. Each detector contains 80 electrodes which are 160 nm wide, 60 mm long and separated by gaps of 370 nm. The full electron microscope functionality of the instrument is maintained to enable the results of the electron beam lithography to be analysed. q1999 Elsevier Science B.V. All rights reserved