Observation of diameter dependent carrier distribution in nanowire-based transistors

Abstract

The successful implementation of nanowire (NW) based field-effect transistors (FET)critically depends on quantitative information about the carrier distribution inside suchdevices. Therefore, we have developed a method based on high-vacuum scanning spreadingresistance microscopy (HV-SSRM) which allows two-dimensional (2D) quantitative carrierprofiling of fully integrated silicon NW-based tunnel-FETs (TFETs) with 2 nm spatialresolution. The key elements of our characterization procedure are optimized NWcleaving and polishing steps, the use of in-house fabricated ultra-sharp diamond tips,measurements in high vacuum and a dedicated quantification procedure accounting for theSchottky-like tip–sample contact affected by surface states. In the case of the implantedTFET source regions we find a strong NW diameter dependence of conformality,junction abruptness and gate overlap, quantitatively in agreement with processsimulations. In contrast, the arsenic doped drain regions reveal an unexpectedNW diameter dependent dopant deactivation. The observed lower drain dopingfor smaller diameters is reflected in the device characteristics by lower TFEToff-currents, as measured experimentally and confirmed by device simulations.