Fabrication of apodized surface-acoustic-wave interdigital transducers by electron image projection

Summary form only given. Use of a narrow slit as an electron-optical lens for forming patterns of lines having submicron linewidths and interline spacings by electron image projection rather than by pattern tracing with an SEM is reviewed. Initial applications of this “slit-lens” technique were to forming interdigital transducers having the same overlap for all finger pairs (no “apodization”), and delay lines were produced on LiNbO₃ for operation up to 2.8 GHz (~0.33-μm lines on ~0.66-μm centers). A recently developed variant of this technique for fabricating transducers having overlap-weighted apodization is presented and its application to the fabrication of a Hamming-weighted device is described. The basic imaging technique involves application of several kV dc between a conductive plate having a narrow slit and the nearby resist-coated target or substrate; a low-energy electron beam passing through the slit from a relatively distant source is converged only in the direction transverse to the slit by the field, thereby producing a line image on the target having a much smaller width than the slit. Object patterns for a slit lens consisting of properly designed arrays of apertures (illuminated with an electron gun) are used in conjunction with appropriately placed interdigitation or apodization masks to yield the desired image patterns on the target, with large demagnification factors in linewidths and spacings.