In a recent letter [Lauinger et al., Appl. Phys. Lett. 68, 1232 (1996)] we have shown that record low effective surface recombination velocities S-eff of 4 cm/s have been obtained at ISFH on low-resistivity (1 Ohm cm) p-type crystalline silicon using microwave-excited remote plasma-enhanced chemical vapor deposition (RPECVD) of silicon nitride at low temperature (300-400 degrees C). As an important application, this technique allows a simple fabrication of rear-passivated high-efficiency silicon solar cells with monofacial or bifacial sensitivity, In this work, we present details of the required optimization of the PECVD parameters and a characterization of the resulting silicon nitride films. All deposition parameters are shown to strongly affect S-eff as well as the stability of the films against the ultraviolet (UV) photons of terrestrial sunlight. A clear correlation between S-eff and the film stoichiometry is observed, allowing a simple control and even a rough optimization of the surface passivation quality by measurements of the refractive index of the films. An optimum passivation and UV stability is obtained for silicon-rich silicon nitride films with a refractive index greater than 2.3.