An integrated circuit chip includes a buffer layer, an underlying layer, a dielectric layer, a hole, and barrier layer. The buffer layer is over the underlying layer. The dielectric layer is over the buffer layer. The hole is formed in and extending through the dielectric layer and the buffer layer, and opens to the underlying layer. The hole includes a buffer layer portion at the buffer layer and a dielectric layer portion at the dielectric layer. At least part of the buffer layer portion of the hole has a larger cross-section area than a smallest cross-section area of the dielectric layer portion of the hole. The conformal barrier layer covers surfaces of the dielectric layer and the buffer layer in the hole. The hole is a via hole or a contact hole that is later filled with a conductive material to form a conductive via or a conductive contact.