Abstract: The present invention provides a method for forming low dielectric constant inter-metal dielectric layer. The method comprises providing a semiconductor substrate and forming a first dielectric layer on the semiconductor substrate. Conductor structures are formed in the first dielectric layer. The partial first dielectric layer is removed by using the conductor structures as etch mask. A second dielectric layer is formed between the conductor structure, which has a dielectric constant smaller than the first dielectric layer. The semiconductor structure comprises a substrate, a first dielectric layer on the substrate, multitude of conductor structures in the first dielectric layer, and multitude of second dielectric structures in the first dielectric layer and between the conductor structures.