Ultra-shallow dopant diffusion from pre-deposited RPCVD monolayers ofarsenic and phosphorus

Reduced-pressure chemical-vapor-depositions (RPCVD) of arsenic and phosphorus monolayers on silicon are investigated as a damage-free source of ultra-shallow dopant diffusion when encapsulated under a deposited oxide. The encapsulation enhances the diffusion into the Si as compared to doping from the gaseous phase, which is confirmed by sheet-resistance measurements and current-voltage characterization of contacts and diodes fabricated with these layers. The latter show the transition from a p-Schottky diode to an n ⁺p diode with increasing annealing temperature on p-doped samples. This effectively represents the means for SBH modulation by ultra-shallow doping. Process simulations have been found inadequate to describe the diffusion process, which, instead, was found to be a mixture of at least two physical mechanisms.