N-type polysilicon passivating contacts using ultra-thin PECVD silicon oxynitrides as the interfacial layer

Abstract

We describe the optimization of an ultra-thin silicon oxynitride (SiOxNy) layer deposited by plasma enhanced chemical vapor deposition (PECVD) as an interfacial layer for phosphorus doped polysilicon (poly-Si) passivating contacts. Our results demonstrate the possibility of depositing the thin interfacial layer and the intrinsic amorphous silicon (a-Si) film in a single PECVD process. We found that the gas flow rates strongly influence the properties of the SiOxNy layers, such as the refractive indices, chemical bond compositions and structural stabilities, which significantly affect the properties of the resulting polysilicon passivating contact structures. The passivation quality initially increased and then decreased with a decreasing N2O/SiH4 flow ratio, in the gas flow range of uniform deposition, while the contact resistivity decreased significantly. We found an optimal gas flow ratio of N2O:SiH4:N2 = 25:9:361, with which we obtained uniform polysilicon passivating contacts with a high implied open-circuit voltage (iVoc) of 711 mV and a low contact resistivity ρc of 6.6 mΩ cm2.