Silicon nitride (SiNx:H) films are generally used as passivation and anti-reflection layers in solar cells, and they are usually made by plasma-enhanced chemical vapor deposition (PECVD). Silicon nitride could act as a hydrogen diffusion source, and it also plays a role in chemical passivation. In this study, we investigated the improvement of the passivation characteristics of the passivated contact structure by a PECVD SiNx:H hydrogenation process and the characteristics of SiNx: H for improving the passivation characteristics. It was confirmed that the passivation characteristics cannot be predicted only by the mass density of the SiNx:H film, and the chemical bonding ratio in the SiNx: H thin film is also important. In addition, higher passivation characteristics can be obtained when SiNx: H thin films with higher S-H bond concentration and dominant N2Si-H-2 bonds are used.