A method of fabricating a semiconductor integrated circuit (IC) is disclosed. A substrate having a dielectric layer over it is provided. A block co-polymer (BCP) layer is deposited over the dielectric layer. The BCP layer is then annealed to form a first polymer nanostructures surrounded by a second polymer nanostructures over the dielectric layer. The second polymer nanostructure is selectively etched using the first polymer nanostructure as an etch mask to form a nano-block. The dielectric layer is selectively etched using the nano-block as an etch mask to form a nano-trench. The nano-trenched is sealed to form a nano-air-gap.