Electron-beam fabrication of quarter-micron T-shaped-gate FETs using a new tri-layer resist system

A LO/HI/LO resist system has been developed to produce sub-half-micron T-shaped cross-section metal lines using electron-beam lithography. The system provides T-shaped resist cavities with guaranteed undercut profiles. T-shaped metal lines as narrow as 0.15µm have been produced. GaAs FETs with 0.25µm T-shaped gates have also been fabricated using this resist system. Measured end-to-end 0.25µm gate resistance was 100ω/mm gate width. At 18GHz, a maximum stable gain of 13.8dB and a minimum noise figure of 2.0dB were measured. The 0.25µm T-gate FETs have a cutoff frequency
f_{T} \sim 50
GHz.