Single step electron-beam lithography for asymmetric recess and gamma gate in high electron mobility transistor fabrication

Abstract

We have developed an asymmetric recess etch in conjunction with a gamma metal gate process for the fabrication of high electron mobility transistors (HEMTs). This process is based on direct electron-beam lithography with a single exposure of a three stack poly(dimethylglutarimide) and poly(methylmethacrylate) photoresists. It can modify the voltage drop over a wider region fabricated by the so called wide-recess technique as compared with the conventional approach, while maintaining a low source resistance, to reduce the electric field intensity at the gate edge, and therefore enhance the breakdown voltage. This gate engineering process for the 0.2 μm InAlAs/InGaAs metamorphic HEMTs achieved a 45% off-state breakdown voltage improvement as compared with the traditional bilayer T-gate device.