Studying dopant diffusion from Poly-Si passivating contacts

The diffusion of dopants from the poly-Si layer through the interfacial oxide into the crystalline silicon wafer is studied experimentally and via numerical simulation. It is found that phosphorus piles up at the poly-Si/SiOx interface but boron readily diffuses through the oxide into the silicon and thereby forms a less shallow junction which adversely affects surface passivation. Although boron diffusion was suppressed by using a nitrided oxide – realized by a plasma oxidation process – a reduction in passivation was observed due to deterioration of the interface. Via 1D and 3D process simulation it was established that diffusion through pinholes contributed little to the aggregate diffusion profiles measured by ToF-SIMS but direct diffusion through the oxide was the main diffusion mechanism. The segregation coefficient at the poly-Si/SiOx interface and the diffusivity in SiOx were determined. Using these parameters simulation-based predictions were conducted in order to pave the way for future optimization of hole-selective passivating contacts.