Sub-0.2-μm lithography by using a variable-shaped electron beam assisted by a focused ion beam process

Abstract

Sub-0.2-μm lithography processes have been developed by using a variable-shaped electron beam (EB) assisted by a focused ion beam (FIB). This process has been applied to the mushroom-gate fabrication of low-noise high electron mobility transistors. By use of a 320 keV Si++ and a shaped EB of 0.1 μm×4.0 μm, the mushroom gate was fabricated in dimensions of ∼0.15 μm. The overlay errors were <0.2 μm both for ‘‘top’’ and ‘‘bottom’’ gates, which were respectively written by FIB and EB. The ‘‘bottom’’ gates were especially exposed for only 48 min per 15 000 devices together with the gate pads.