Abstract: A single-level photoresist process is used to make metal-semiconductor field-effect transistors (MESFETs) having more uniform threshold voltages. An N.sup.- layer is formed in a semi-insulating semiconductor, followed by formation of a dummy gate using a single-level photoresist process. Using the dummy gate as a mask, ions are implanted to form an N.sup.+ region. The length of the dummy gate is then reduced by plasma etching. A dielectric is deposited over the N.sup.+ region, the N.sup.+ /N.sup.- interface, and the exposed portion of the N.sup.- layer. The dummy gate is lifted off to define a self-aligned, submicron gate opening. The gate opening on the N.sup.- layer is reactive ion etched to obtain the desired threshold voltage, and covered with a Schottky gate metal deposit.

Abstract: Focused ion beam microfabrication column (10) produces an ion beam from ion source (12), focuses the beam by objective lens (24) onto the plane of electrode (36). ExB filter (44) separates out the ion species at a low energy portion of the beam. The beam of selected species is first accelerated by energy central lens (38) which has a controllable potential for controlling the final beam energy to the target. The beam is accelerated by final accelerator lens (54) and is demagnified and focused on the target by that lens. Beam deflector (64) deflects the beam for programmed ion beam work on the target (60).

Abstract: The ExB mass separator provides a magnetic field B normal to the beam path and potential plate for applying an electric field normal to the magnetic field for maintaining the selected ions in beam 32 along a defined path. Along the path, after the major portion of the unwanted species are deflected from the beam, focus plates 34 and 36 focus the selected species toward the separator opening 38. Downstream potential plates 28 and 30 maintain the defined path for the selected species.