Vertical <i>n</i> <i>p</i> <i>n</i> transistors by maskless boron implantation

Abstract

The use of a focused ion beam (FIB) system with a 0.2 μm beam diameter to fabricate npn bipolar transistors by maskless implantation of B (75 keV, 30 mA/cm2) is described. Devices with a conventional boron implant are fabricated on the same wafer. The material (SIMS profile, Rs) and electrical properties (transistor I–V characteristics) of the FIB implants are comparable to those for conventional implants. Initial evaluation suggests that the lateral spread of the implanted area is &amp;lt;0.1 μm. The similarity in results between the two implant processes demonstrates that the FIB system is functioning as designed (no serious problems with beam pointing stability, target current fluctuations, or introduction of impurities, etc.) and that no significant differences in beam target interactions (dopant distribution, percent activation, residual defects, etc.) occur. Application of an FIB lateral base implant to prevent emitter current crowding is discussed and the fabrication of transistors with lateral profiles demonstrated.