Focused Ion Beam Fabrication of Silicon-On Field-Effect Transistors.

N-channel metal-oxide-semiconductor field-effect transistors (MOSFET's) have been fabricated on silicon -on-insulator (SOI) substrates using a Focused Ion Beam (FIB) to pattern the gate and to dope the source and drains. Lightly -doped source (LDS) structures were implemented with the FIB to increase the drain-to-source voltage at which single transistor latch-up occurred. FIB exposure of two electron-beam resists was investigated for lithography of the transistor gate and the device mesas. Vertical resist profiles were achieved for linewidths down to 0.2 μm in width in the case of the negative-tone SAL-601 resist from Shipley Co. Openings in resist as narrow as 0.35 μm were made using the positive-tone P28 resist from OCG Microelectronic Materials. Optimal doses, pre- and post-exposure processing conditions were determined for both resists. Transistors with LDS structures showed higher latching voltages than those without. The magnitude of the increase in latching voltage due to the LDS was a function of body doping level, SOI thickness, and coded gate length. The largest increase was 5.1 V for a 0.8 μm MOSFET fabricated in a 125 nm thick SOI film with a body implant dose of 5.6times10^ {12} B cm^{-2}. Devices fabricated in SOI films of thickness 250 nm showed smaller increases in latching voltage with the LDS than those in 125 nm SOI films.