本发明提供一种即便于氧化物半导体膜上直接形成氟化硅氮化膜亦可抑制该氧化物半导体膜的电阻降低的膜形成方法。该膜形成方法包括：表面处理步骤40，准备于基板上具有氧化物半导体膜的物品，使用氧与氢的混合气体且氢的比例为8%以下（不包括0）的混合气体来生成等离子，并借由该等离子对氧化物半导体膜的表面进行处理；成膜步骤42，其后借由使用含有四氟化硅气体及氮气的原料气体而生成等离子的等离子CVD法，于所述氧化物半导体膜上形成氟化硅氮化膜（SiN：F膜）；以及退火步骤44，其后对所述基板及该基板上的膜进行加热。

Provided is a film formation method that makes it possible to minimize decreases in the electrical resistance of an oxide semiconductor film even when a fluorinated silicon nitride film is formed directly on the oxide semiconductor film. The film formation method is provided with: a surface treatment step 40 in which a substance comprising an oxide semiconductor film on a substrate is prepared, plasma is generated using a mixed gas of oxygen and hydrogen which contains hydrogen at a rate of 8% or less (not including 0), and the plasma is used to treat the surface of the oxide semiconductor film; a film formation step 42 in which a fluorinated silicon nitride film (a SiN:F film) is subsequently formed on the oxide semiconductor film by a plasma CVD method in which plasma is generated using a raw material gas containing silicon tetrafluoride gas and nitrogen gas; and an annealing step 44 in which the substrate and the film thereon are subsequently heated.