A method for forming a semiconductor structure includes providing an initial semiconductor structure formed in a substrate; forming a dielectric layer on the substrate; forming a first opening in the dielectric layer to expose a portion of the initial semiconductor structure; etching the portion of the initial semiconductor structure exposed at a bottom of the first opening to form a second opening in the initial semiconductor structure; and forming a contact layer in the second opening and a third opening in the contact layer. The contact layer has a concave top surface, and the third opening is located above the concave top surface of the contact layer and under the first opening. The method further includes forming a conductive structure in the first opening and the third opening.