Electron Beam Fabrication of High Performance InGaAs/InAlAs HIGFETs with Submicron Refractory Airbridge Gates

Self-aligned HIGFET devices with gate lengths as short as 0. 125microns (nominal) have been fabricated on MBE grown InAlAs/InGaAs/InP heterostructures using electron beam lithography. A bi-level resist comprising PMMA and P(MMA/MAA) is exposed in a 50 kV e-beam lithography system and is used to liftoff a removable etch mask material. 

Reactive ion etching (RIE) is used to define a tungsten gate, followed by implantation of Si sup + to form the self-aligned source and drain contract regions. Tungsten air bridges are formed during the mesa isolation step to provide the lowest gate leakage current and capacitance. Results from preliminary microwave electrical measurements are presented for devices with gate lengths as short as 0.25micron.