FABRICATION OF Y-GATE, SUBMICRON GATE LENGTH GAAS METAL-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS

0.1 mum Y-shape metal contacts for use as gates on GaAs metal-semiconductor field effect transistors (MESFETs) are produced using a novel SiN(x) deposition over features 1-2 mum wide, with subsequent etchback and gate metal deposition. Excellent across-wafer uniformity (less-than-or-equal-to 10%) on 3 in. Phi substrates is achieved, yielding a simple technique for extending the resolution of conventional optical lithography tools. One of the key features in this method is the need to have an initial negative resist profile. The SiN(x) is deposited at low temperature (50-degrees-C) by plasma-enhanced chemical vapor deposition in order to avoid distortion of the resist, and exhibits conformal coverage over the initial resist openings. Submicron gate GaAs MESFETs fabricated by this technique have extrinsic transconductance, g(m), value of approximately 225 mS mm-1 at -0.5 V gate bias, and have comparable performance to devices fabricated using electron-beam lithography to produce a more conventional T-shape gate.