Development of a SEM Microlithography System: Application to GHz Surface Acoustic Wave Devices

Abstract

<p>This thesis concerns itself with the design and implementation of an electron beam lithography system. A novel microcomputer-controlled vector-scan pattern generator was constructed and interfaced to a commercially available scanning electron microscope (SEM). A software monitor program was incorporated into the 8-bit microcomputer, which allows pattern data entry in decimal coordinates via a keyboard/display interface, and subsequent storage of the coded data on cassette tape.</p> <p>The usable scan field size for accurate pattern exposure in the Stereoscan Mark II A SEM has been determined to be 1mm x 1mm. The electron beam lithography system was used to scan a 1 GHz surface acoustic wave (SAW) delay line pattern, which featured a total of 480 fingers, each 7,680 Å in width. Polymethylmethacrylate (PMMA) electron-sensitive resist was used for the pattern exposures, and a linear charge density of 1 x 10ˉ⁸ C/cm was used. The lift-off fabrication process was used to obtain the final device circuit features. The resulting delay line exhibited an untuned insertion loss of 24.3 dB, and was subsequently incorporated into the feedback loop of an amplifier with excess gain to form a SAW oscillator.</p> <p>Several other circuit patterns were scanned, including a 2 GHz SAW delay line with 3000 Å linewidths, and sub-micron bubble memory T-I bar circuits. Details of all the scanning parameters are given, along with the pattern exposure results.</p>