NOVELTY - The film formation method involves forming a silicon nitride film (1) on a resin substrate (10) with organic layer and installed in a reaction container (110) for chemical vapor deposition (CVD) using plasma. The silicon nitride film is formed on the resin substrate below the allowable temperature limit of the organic layer, and with the use a source gas containing silane, ammonia and hydrogen. The ratio of hydrogen with respect to the silane in the source gas is 13 to 20 percent, while the ratio of ammonia with respect to the silane is 13 to 24 percent.    USE - Silicon nitride film formation method used in making image display devices with resin substrate e.g. LCD, organic electroluminescent device, electronic paper, dye-sensitized solar cell, touch panel.    ADVANTAGE - Forms a silicon nitride film with favorable film quality and with high efficiency at a film forming temperature below the allowable temperature limit of the organic layer formed on the resin substrate. Laminates the formed silicon nitride film onto an organic layer at a predetermined water vapor permeation rate to form a gas barrier with predetermined gas barrier property.    DETAILED DESCRIPTION - The source gas containing silane, ammonia and hydrogen is supplied into the reaction container, such that its total gas pressure is set into atmospheric pressure. Electric field is applied to an electrode (111) installed above the resin substrate to generate an electric field between the electrode and resin substrate, and to set the source gas in plasma state between the electrode and substrate. INDEPENDENT CLAIMS are also included for the following:    (1) Silicon nitride film;    (2) Gas barrier film formed using the silicon nitride film; and    (3) Thin film device formed using the gas barrier film.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic representation showing the atmospheric pressure plasma-CVD apparatus of rotating electrode system used for forming the silicon nitride film.    Silicon nitride film (1)    Resin substrate (10)    Atmospheric pressure plasma-CVD apparatus (100)    Reaction container (110)    Electrode (111)