The interlayer dielectric film made of a three-dimensionally polymerized polymer is formed by polymerizing: first cross-linking molecules having three or more sets of functional groups in one molecule providing a three-dimensional structure; and a second cross-linking molecule having two sets of functional groups in one molecule providing a two-dimensional structure. In the three-dimensionally polymerized polymer, dispersed are a number of molecular level pores formed by the polymerization of the first and second cross-linking molecules.