In a method of treating a target film, a plurality of pattern structures with sidewall surfaces facing each other are provided. A target film is formed on the sidewalls of the plurality of pattern structures. A plurality of nanoparticles are distributed on the target thin film. The target thin film is thermally treated by irradiating laser light from upper sides of the plurality of pattern structures to the target thin film. The irradiated laser light is scattered from the plurality of nanoparticles.