An inter-layer dielectric structure and method of making such structure are disclosed. A composite dielectric layer comprising a porous matrix, as well as a porogen in certain variations, is formed adjacent a sacrificial dielectric layer. Subsequent to other processing treatments, a portion of the sacrificial dielectric layer is decomposed and removed through a portion of the porous matrix using supercritical carbon dioxide leaving voids in positions previously occupied by portions of the sacrificial dielectric layer. The resultant structure has a desirably low k value as a result of the voids and materials comprising the porous matrix and other structures. The composite dielectric layer may be used in concert with other dielectric layers of varying porosity, dimensions, and material properties to provide varied mechanical and electrical performance profiles.