Polycrystalline Ge Nanosheets Embedded in Metal‐Semiconductor Heterostructures Enabling Wafer‐Scale 3D Integration of Ge Nanodevices with Self‐Aligned Al Contacts

Abstract

The ability to stack nanosheet transistors is an important prerequisite for the realization of vertically monolithic 3D integrated circuits enabling higher integration densities of functions and novel circuit topologies that relax miniaturization constraints. In this respect, a wafer‐scale platform is presented embedding high‐quality nanoscale polycrystalline Ge channels into monolithic metal‐semiconductor heterostructures. Thereto, a fabrication scheme comprising a combination of flash lamp annealing, crystallizing ultra‐thin amorphous Ge nanosheets, and a thermally induced Al‐Ge exchange reaction is demonstrated, facilitating the formation of self‐aligned Al leads enabling sharp Al‐Ge heterojunctions. The high quality of the obtained polycrystalline Al‐Ge‐Al heterostructure nanosheets is confirmed by µ‐Raman, scanning transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, and electron backscatter diffraction measurements. Embedded in back‐ and top‐gate field‐effect transistor architectures, the electrical transport in polycrystalline Al‐Ge‐Al heterostructures is systematically analyzed. Enabling a complementary metal‐oxide‐semiconductor compatible wafer‐scale accessibility of high‐quality polycrystalline Ge with self‐aligned Al contacts, the proposed platform significantly contributes to the development of a broad spectrum of emerging 3D integrated Ge nanodevices.

Monolithic and Single-Crystalline Aluminum–Silicon Heterostructures

“…Importantly, material combinations with no intermetallic phase formation can overcome difficulties in the precise and reproducible definition the crystal phase and stoichiometry of the intruded metallic segments. These systems enable single-elementary metal–semiconductor heterostructures and have received strong attention. − However, up to now, monolithic heterostructures between elementary metal and Si are still elusive, which is mainly attributed to either stress-induced voiding and void nucleation via electromigration − or interdiffusion, causing unwanted doping. − …”

Solid-phase crystallization of ultra-thin amorphous Ge layers on insulators

“…Ultra-thin semiconductor films on insulators possessing high carrier mobility are desired for nanoelectronics applications such as 3D integrated circuits and memories. [1][2][3][4][5][6][7] Germanium (Ge) is one of the attractive materials due to its high carrier mobility and good compatibility with the Si integrated circuits process. [8][9][10][11][12][13] Many researchers have developed crystal growth techniques for Ge on an insulator in the recent quarter-century.…”