A file is formed by coating a substrate with a film-forming composition including a compound having an alicyclic hydrocarbon structure and irradiating the coated composition with microwaves having a frequency of 5.8 GHz. An insulating film is formed by irradiating a film including a compound having a siloxane structure with microwave having a frequency of 5.8 GHz. These films possess excellent film properties such as dielectric constant and mechanical strength.