Metal-induced dopant (boron and phosphorus) activation process in amorphous germanium for monolithic three-dimensional integration

In this work, we investigate a low temperature boron (B) and phosphorus (P) activation in amorphous $(α)-Ge$ using metal-induced crystallization technique. Eight candidates of metals (Pd, Cu, Ni, Au, Co, Al, Pt, and Ti) are used to crystallize the $α-Ge$ at a low temperature. Resistivity measurement, transmission electron microscopy, and x-ray diffraction analyses reveal behaviors of the metal-induced dopant activation process using the metals reacting with $α-Ge$⁠. It is revealed that Co achieves the highest B and P activation ratio in Ge below $360°C$ with a slow diffusion rate. This method can be utilized to activate gate, source, and drain of transistors on upper layers in three-dimensional integrated circuits, where low temperature processing is critical.