Fabrication of 35-nm zigzag T-gate Al0.25Ga0.75As/In{0.2}Ga{0.8}As/GaAs pHEMTs

In this paper, a novel process using two-step electron beam lithography and zigzag T-gate method is proposed to fabricate 35-nm T-gates and demonstrated by fabricating high performance Al_o.25Ga_o.75As/in_o.2Ga_o.8As/GaAspHEMTs . Two-step lithography adopting a low temperature development method reduces electron forward scattering and the detrimental effect of the head exposure on foot definition. Thus, this method enables 35-nm T-gate patterning using a tri-layer (PMMA-MAA/PIVIGI/PIV1MA) resist structure under a low 20 keV electron beam acceleration condition. The zigzag style T-gate enhances mechanical support for the 35-nm T-gate to remain standing after metal lift-off process. It is shown here that 35-nm zigzag T-gate Al_o.25Ga_o.75As/in_o.2Ga_o.8As/GaAspHEMTs with f_r of 200 GHz can be realized using this process.