A method for forming a porous dielectric material layer in an electronic structure and the structure formed are disclosed. In the method, a porous dielectric layer in a semiconductor device can be formed by first forming a non-porous dielectric layer, then partially curing, patterning by reactive ion etching, and final curing the non-porous dielectric layer at a higher temperature than the partial curing temperature to transform the non-porous dielectric material into a porous dielectric material, thus achieving a dielectric material that has significantly improved dielectric constant, i.e. smaller than 2.6. The non-porous dielectric material may be formed by embedding a thermally stable dielectric material such as methyl silsesquioxane, hydrogen silsesquioxane, benzocyclobutene or aromatic thermoset polymers with a second phase polymeric material therein such that, at the higher curing temperature, the second phase polymeric material substantially volatilizes to leave voids behind forming a void-filled dielectric material.