Charge stability in LPCVD silicon nitride for surface passivation of silicon solar cells

Negatively charged dielectric films are of great interest for application to silicon solar cells, since such films offer the possibility of excellent passivation of p type surfaces. This paper investigates the distribution and stability of negative charge in silicon dioxide / LPCVD silicon nitride films which have been negatively charged through the injection of electrons from the silicon substrate. High densities of negative charge (5-10×10¹²cm^-2) can be stored in the silicon nitride films. The negative charge is determined to be mainly concentrated at the oxide/nitride interface. The thermal stability of the charge is shown to be improved by the presence of a barrier layer on top of the silicon nitride. Modelling indicates that the thermal stability is likely to be sufficient for application to solar cells, which will operate at elevated temperatures for 25 years or more.