GaAs FET Device Fabrication and Ion Implantation Technology

Abstract : Microwave device fabrication and evaluation in conjunction with ion implantation has been selected to provide a benchmark technology for evaluation of semi-insulating GaAs and InP grown at NRL and elsewhere. Devices have been processed by a combination of conventional contact photolithography and liftoff techniques to achieve geometries with linewidths as small as 0.8 microns. A plasma deposited layer of Si3N4 has been employed as an annealing encapsulant at temperatures between 800 C and 850 C for 15-30 minutes (GaAs) or 700 C-750 C for 15 minutes (InP). Si and Se were used as the principal implant species. During this period, the Si3N4 encapsulation process and the fabrication of GaAs FETs with one micron gate lengths and noise figures below 2.4 dB at 6 GHz have become routine. Difference in microwave performance between ion implanted channel and epitaxial channel (industrially supplied) GaAs FETs was systematically correlated with various materials parameters such as mobility and light sensitivity and with static FET characteristics such as looping, backside gating, pinch-off voltage and transconductance. Experimental results indicate that good microwave performance can be obtained even though a few of the static or material characteristics are independently judged to be substandard.