First Demonstration of Vertical Sandwich GAA TFETs with Self-Aligned High-k Metal Gates and Abrupt Doping Tunneling Junctions

Abstract

A new type of vertical sandwich gate-all around tunneling field-effect-transistors (GAA TFETs), called VSATFETs, was demonstrated firstly with a CMOS-compatible process. The VSATFETs with self-aligned high-κ metal gates (HKMG) and abrupt doping tunneling junctions were fabricated with the epitaxial of p+-Si/i-SiGe/n+-Si sandwich structure and an isotropic quasi-atomic layer-etch (qALE) process. VSATFETs have the advantage of excellent control of channel size, because its gate-length is mainly determined by the thickness of SiGe film grown by epitaxy, and the diameter of the nanowires (NWs) /thickness of nanosheets (NSs) is determined by the qALE etching of SiGe selective to Si. A NW VSATFET with a diameter of 18 nm was fabricated and exhibits excellent characteristics: SSmin = 61.64 mV/dec, Ion = 2.25 x 10-7 A/um (@Vgs-Vt = 0.45 V, Vd = 0.65 V), Ion/Ioff = 1.81 x 106, DIBL = 7.58 mV. The effect of interface traps on the device performance was analyzed by the calibrated model. It is found that the device performance can be improved by decreasing the thickness/diameter of NS/NW TFET.