GaAs/AlGaAs HEMT's with sub 0.5 mym gatelength written by E-beam and recessed by dry-etching for direct-coupled FET logic -DCFL-

High electron mobility transistor (HEMT) structures were grown on two-inch GaAs wafers by molecular beam epitaxy. Enhancement and depletion FETs (E- and D-FETs) with 0.3 mym gatelength were fabricated using e-beam direct-write lithography. The double layer resist technique has been extensively investigated to improve the reliability of 0.3 mym e-beam lithography. The vertical structure which is relevant for the dry etching process, included two GaAs layers of 30 nm and 7.5 nm and two thin (3 nm) Al sup 0.3Ga sup 0.7 As etch stop layers to control precisely the depth of the etch recess. Using this technology we fabricated DCFL circuits such as demultiplexers, frequency dividers and ring oscillators.