A method for fabricating an integrated circuit structure includes the steps of forming a second dielectric layer on a substrate including a first conductive layer and a first dielectric layer, forming the second dielectric layer on the first conductive layer and the first dielectric layer, forming a hole exposing the first conductive layer in the second dielectric layer, forming a barrier layer inside the hole, and forming a second conductive layer on the barrier layer. In one embodiment of the present invention, the forming of the barrier layer comprises the steps of forming a metal layer in the hole, and performing a treating process in an atmosphere including a plasma formed from a gas including oxidant to form a metal oxide layer on the metal layer. In another embodiment of the present invention, the forming of the barrier layer comprises the steps of forming a metal nitride layer in the hole, and performing a treating process in an atmosphere including a plasma formed from a gas including oxidant to form a metal oxide layer on the metal and metal nitride layer.