Vertical N-Type and P-Type Nanosheet FETs With C-Shaped Channel

We presented and demonstrated both n- and p-type vertical C-shaped-channel nanosheet field-effect transistors (VCNFETs) featured with precise control of both channel thickness and gate length. The VCNFETs were fabricated by high-quality Si/SiGe epitaxy and atomic layer deposition to obtain nanometer-scale process control and self-aligned high-
${k}$
metal gate (HKMG). The integration flow is compatible with the process used in the mainstream industry and it can be easily extended to vertically stacked devices. Both the gate length and the channel thickness of the VCNFETs are mainly determined by the thicknesses of Si/SiGe films grown by epitaxy, instead of lithography and etch techniques. Perfect subthreshold swing (SS), small drain-induced barrier lowering (DIBL), and large
${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$
ratio were achieved for both n- and p-VCNFETs due to the crystalline silicon channel and the well-defined doping profiles. The device performance and optimization were also investigated and discussed. Used as access transistors in dynamic random access memory (DRAM) array, VCNFETs were also demonstrated for the potential applications to 10-nm DRAM and beyond.