The relationship between aluminum fire-through and the properties of a-SiNx:H thin films was investigated to aid their use as dielectric layers in rear side and front passivation layers in crystalline solar cells. Aluminum fire-through was shown to depend on the refractive index and the deposition rate of the films. Refractive index, density and deposition rate increased with increasing SiH4/NH3 ratio, while the etching rate decreased. Aluminum fire-through occurred in a sample of refractive index 2.0 during fast deposition but not when the deposition rate was slow. Aluminum fire-through occurred during extended firing, despite it not occurring during normal firing by RTP. The results of this work demonstrate that refractive index was the major determinant of aluminum fire-through, and that the aluminum and the a-SiNx:H thin film reacted immediately at the beginning of firing at a rate determined by the deposition rate. (C) 2011 Elsevier B. V. All rights reserved.