Selective solid-phase silicon epitaxy of p⁺ aluminum-doped contacts for nanoscale devices

A solid-phase epitaxy (SPE) process based on material inversion of an amorphous silicon (α-Si) on aluminum layer-stack is applied to form ultrashallow p-type junctions. In this paper, we demonstrate the controllability of the whole process when the junction area is reduced to the sub-100-nm range and the processing temperature is reduced to 400°C. The SPE-Si to Si-substrate interface, analyzed locally by transmission electron microscopy and more systematically by the fabrication and electrical characterization of p⁺ -n diodes, was found to be practically defect-free. Moreover, it is demonstrated by capacitance-voltage profiling that the Al-dopants do not diffuse into the bulk silicon for the used processing temperatures and the SPE p⁺ -island to n-substrate transition is ideally abrupt. The I-V characteristics of the as-fabricated p⁺-n diodes are near ideal (n = 1.03) and low-ohmic contact resistance to p^- and p⁺ regions is reliably obtained.