Surface passivation of p-type crystalline silicon wafers by means of phosphorus-dopedhydrogenated amorphous silicon carbide films [a-SiCx(n):H] has been investigated. Particularly, wefocused on the effects of layer thickness on the c-Si surface passivation quality resulting in thedetermination of the fixed charge density, Qf, within the a-SiCx(n):H film and the fundamentalrecombination of holes, Sp0. The main result is that surface recombination velocity decreases withfilm thickness up to 40 nm and then saturates. The evolution of the interface parameters indicatesthat Qf could be located in a layer less than 10 nm thick. In addition, Sp0 increases with thinner filmsprobably due to different hydrogenation and saturation of interface dangling bonds during forminggas annealing.