NOVELTY - The barrier film comprises silicon nitride. An atom ratio (N/(Si+N)) indicating a ratio of nitrogen to silicon is 0.60-0.65. The barrier film is formed by a surface wave plasma chemical vapor deposition (CVD) device, and is formed on the substrate mounted on the stage by reacting a silicon nitride gas and an ammonia gas emitted from a film formation gas outlet with free radicals formed with the surface wave plasma. The surface wave plasma CVD apparatus comprises: a dielectric window (4) for introducing microwave; and a discharging gas outlet (5) for emitting a discharging gas.    USE - The barrier film is useful for a transparent substrate such as a plastic substrate, and for sealing a flexible semiconductor device such as an organic semiconductor-containing light emitting device, an organic semiconductor-containing photovoltaic conversion device, an organic semiconductor-containing current control device, an organic electroluminescent device (all claimed), biomedical devices, microelectromechanical systems, top-emission type organic electroluminescent display devices, LCD devices and solar cells.    ADVANTAGE - The barrier film can be easily, rapidly, efficiently, economically and reliably fabricated with high barrier performance and light transmittance, high water vapor permeability, increased impact resistance and flexibility and long life span at a low temperature.    DETAILED DESCRIPTION - The barrier film comprises silicon nitride. An atom ratio (N/(Si+N)) indicating a ratio of nitrogen to silicon is 0.60-0.65. The barrier film is formed by a surface wave plasma chemical vapor deposition (CVD) device, and is formed on the substrate mounted on the stage by reacting a silicon nitride gas and an ammonia gas emitted from a film formation gas outlet with free radicals formed with the surface wave plasma. The surface wave plasma CVD apparatus comprises: a dielectric window (4) for introducing microwave; a discharging gas outlet (5) for emitting a discharging gas; the film formation gas outlet for emitting a film formation gas; a stage for mounting a substrate; and a variable unit for changing a distance between the stage and surface wave plasma that is formed near the dielectric window with the discharging gas emitted from the discharging gas outlet. The distance between the stage and the surface wave plasma is adjusted by the variable unit to form the barrier film in a state that the temperature of the substrate mounted on the stage is less than or equal to 200 degrees C. An INDEPENDENT CLAIM is included for a method for forming a barrier film.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic vertical cross-sectional view of a plasma chemical vapor deposition apparatus.    Microwave (1)    Wave guide (2)    Slot antenna (3)    Dielectric window (4)    Discharging gas outlet (5)    Reaction chamber. (6)