The surface passivation is one of the crucial steps to achieve high conversion efficiencies in c-Si solar cells. A thermally stable thin film with a negative charge (for p-type surface) passivation layer is required to develop a good front passivation suitable for n-type c-Si solar cells. Silicon suboxide (SiOX) layer using PECVD provides a good passivation layer which has low temperature process and charge control in thin-film layer. In this paper, a PECVD stack layer consisting of SiOX and SiNX was employed for front side passivation. The optimal refractive index of SiOX and SiNX were found by varying the silane (SiH4), ammonia (NH3) and nitrous oxide (N2O) gas ratio for decrease optical loss. -1.71 × 10 11 cm -2 of negative charge (Qf) and 5×10 10 cm -2 eV -1 of Dit (interface trap density) were obtained at 10 nm thick SiOX thin-film. With this optimized SiOx/SiNx stack layer on p + surface wafer using PECVD, the effective lifetime of 280 ㎲ and implied VOC of 690 mV were achieved. It is expected that the efficiency of the n-type silicon solar cell can be improved by applying the optimized SiOx condition to the front passivation layer.