In a method of making a semiconductor device, the method includes: forming a first conductive layer over a substrate; forming an insulating layer on the first conductive layer; forming a via through the insulating layer to expose the first conductive layer; forming a self-assembled monolayer (SAM) over a bottom of the via; forming a barrier layer at a sidewall of the via; removing the SAM over the bottom of the via; and forming a second conductive layer over the barrier layer and the bottom of the via such that the first conductive layer is electrically connected to the second conductive layer without the barrier layer between the first conductive layer and the second conductive layer at the bottom of the via.