There is provided a film formation processing method for forming, in a vacuum atmosphere, a silicon nitride film along an inner wall surface of a recess constituting a pattern formed on a surface of a substrate, which includes: forming the silicon nitride film on the substrate by repeating, plural times, a process of supplying a raw material gas containing silicon to the substrate and subsequently, supplying an ammonia gas to the substrate to generate a silicon nitride on the substrate; and subsequently, modifying the silicon nitride film by activating a hydrogen gas and an ammonia gas and supplying the activated hydrogen gas and the activated ammonia gas to the substrate.