Highest-quality surface passivation of low-resistivity p-type silicon using stoichiometric PECVD silicon nitride

The surface passivation properties of silicon nitride (SiN) films fabricated by high-frequency direct plasma-enhanced chemical vapour deposition (PECVD) on low-resistivity (1 Omega cm) p-type silicon solar cell substrates have been investigated. The process gases used were ammonia and a mixture of silane and nitrogen. In order to find the optimum set of SiN deposition parameters, a large number of carrier lifetime test structures were prepared under different deposition conditions. The optimised deposition parameters resulted in outstandingly low surface recombination velocities (SRVs) below 10 cm/s. Interestingly, we find the lowest SRVs for stoichiometric SiN films, as indicated by a refractive index of 1.9. In former studies similarly low SRVs had only been obtained for silicon-rich SiN films. The fundamentally different passivation behaviour of our SiN films is attributed to the addition of nitrogen to the process gases. (C) 2001 Elsevier Science B.V. All rights reserved.