A method for forming of a thin film on a substrate is disclosed. The method includes cleaning a process chamber by flowing a first gas having fluorine. The method also includes coating the process chamber with a first encapsulating layer including amorphous silicon (A-Si) by flowing a second gas for a first duration, where the first encapsulating layer protects against fluorine contamination. The method further includes loading a substrate into the process chamber, depositing a thin film on the substrate by flowing a third gas into the process chamber and unloading the substrate from the process chamber. The thin film can include silicon nitride (SiN), the first gas can include nitrogen triflouride (NF3) gas and second gas can include silane (SiH4) gas. The thin film can be formed using plasma-enhanced chemical vapor deposition. The substrate can be a solar cell or a liquid crystal display (LCD).