To form an insulating film whose burying property and flatness are enhanced, whose permeability is reduced and whose degradation is reduced with reference to an oxygen plasma, by a method wherein a composition is provided with a structure wherein a plurality of phosphorus atoms of phosphonoimide whose main chain is specific are bridged by a specific siloxane bond.

A composition is constituted of a polymer provided with a structure wherein a plurality of phosphorus atoms of phosphonoimide whose main chain is expressed by Formula I are cross-linked by a siloxane bond which is expressed by Formula II. In Formula I, (n) represents an integer of 3 or higher, and Formula II expresses a composition such as dimethyldioxosilicon ((CH3)2Si(O-)2), monomethyltrioxosilicon ((CH3)Si(O-)3) or tetraoxosilicon (Si(O-)4). Thereby, it is possible to form an insulating film whose burying property and flatness are excellent whose dielectric constant is small and whose degradation is small with reference to an oxygen plasma.