Semiconductor structures and fabrication methods are provided. An exemplary fabrication method includes providing a semiconductor substrate having at least a first region; forming a dielectric structure over the semiconductor substrate; forming a plurality of first openings in the dielectric structure in the first region by removing portions of the dielectric structure in the first region; forming a first barrier member in each of the plurality of first openings; forming second openings with sidewall surfaces exposing sidewall surfaces of the first barrier members by removing portions of the dielectric structure between adjacent first openings; and forming a second barrier member in each of the plurality of second openings.