Hydrogenated silicon nitride (SiN x:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. The samples with or without in-situ NH 3 post-plasma treatment had the following structures: SiN x/N-type Si/SiN x versus in-situ NH 3 post-plasma treated SiN x/N-type Si/SiN x. The wafer was dipped in saw-damage-etching solution and wet cleaning process was treated. After the dry process with N 2 atmosphere, SiN x thin film was deposited on back surface. Then SiN x thin film was deposited on the front surface with or without in-situ NH 3 post-plasma treatment process. In order to minimize the plasma induced surface damage, we used lower power than the process power during the NH 3 post-plasma treatment. After the in-situ NH 3 post-plasma-treatment, we analyzed the effect of this in-situ NH 3 post-plasma-treatment for passivation. The minority carrier lifetime was observed by means of quasi-steady-state photoconductance and microwave photoconductance.