The present application provides a method for manufacturing a semiconductor, comprising providing a substrate, on which a first, second and third dielectric layers are successively formed, the third dielectric layer having an initial opening; forming a first deposited layer which at least covers a side wall of the initial opening to form a first mask layer having a first opening; removing the second dielectric layer directly below the first opening to expose a side wall of the second dielectric layer; forming a second deposited layer which at least covers the side wall of the first opening and the exposed side wall of the second dielectric layer, to form a second mask layer having a second opening; removing the first dielectric layer directly below the second opening to expose the substrate; and removing the second mask layer, and forming a trench by etching the substrate.