A method for preparing a semiconductor device, comprising: providing a first dielectric layer; forming a first window in the first dielectric layer; forming a first connection structure in the first window; forming a second dielectric layer on the first dielectric layer, the second dielectric layer having a second window from which at least the first connection structure is exposed; forming a first barrier layer on the sidewall and bottom of the second window; and forming a second connection structure in the second window; wherein the first connection structure comprises a protruded portion of an upper part of the first connection structure, which is protruded above the first dielectric layer at the bottom of the second window, a sidewall of the protruded portion is an inclined sidewall, and the inclined sidewall is inclined at an angle of less than 90° with respect to an upper surface of the first dielectric layer, thereby forming a bulge of the protruded portion which overlaps a portion of the bottom of the second window; and wherein: the first barrier layer is also formed on an upper surface of the protruded portion; a portion of the first barrier layer on the bottom of the second window is discontinuous from a portion of the first barrier layer on the upper surface of the protruded portion, thereby forming an opening in the first barrier layer from which a sidewall of the protruded portion is exposed, a shape of the opening being a ring shape along the circumference of the protruded portion. providing a first dielectric layer; forming a first window in the first dielectric layer; forming a first connection structure in the first window; forming a second dielectric layer on the first dielectric layer, the second dielectric layer having a second window from which at least the first connection structure is exposed; forming a first barrier layer on the sidewall and bottom of the second window; and forming a second connection structure in the second window; wherein the first connection structure comprises a protruded portion of an upper part of the first connection structure, which is protruded above the first dielectric layer at the bottom of the second window, a sidewall of the protruded portion is an inclined sidewall, and the inclined sidewall is inclined at an angle of less than 90° with respect to an upper surface of the first dielectric layer, thereby forming a bulge of the protruded portion which overlaps a portion of the bottom of the second window; and wherein: the first barrier layer is also formed on an upper surface of the protruded portion; a portion of the first barrier layer on the bottom of the second window is discontinuous from a portion of the first barrier layer on the upper surface of the protruded portion, thereby forming an opening in the first barrier layer from which a sidewall of the protruded portion is exposed, a shape of the opening being a ring shape along the circumference of the protruded portion. the first barrier layer is also formed on an upper surface of the protruded portion; a portion of the first barrier layer on the bottom of the second window is discontinuous from a portion of the first barrier layer on the upper surface of the protruded portion, thereby forming an opening in the first barrier layer from which a sidewall of the protruded portion is exposed, a shape of the opening being a ring shape along the circumference of the protruded portion.