In this study, hydrogenated amorphous silicon (a-Si:H) thin films that were deposited by the high density plasma electron cyclotron resonance chemical vapor deposition (ECRCVD) were used to study the passivation effect on the surface of c-Si substrate. We investigated the structural, optical, and passivation qualities of a-Si:H as a heterojunction interface by modulating the parameters of microwave power, substrate temperature, and post-deposition annealing. With increasing the microwave power leading to more dangling bonds, such that the longer lifetime and lower microstructure factor R* were demonstrated at 500W. When raising the substrate temperature, the hydrogen content (CH) will be decreased but the lifetime will be increased because this R* is a dominated factor. It indicates that exceeding 120°C in the substrate temperature has better absorption to the light. In addition, the postdeposition annealing of a-Si:H was an effective method to improve the minority carrier lifetime, and we can obtain better passivation with the carrier lifetime of 883μsec after 2 minutes annealing at 270°C.