A method comprises forming a low-dielectric constant (low-k) layer over a semiconductor substrate, forming an anti-reflective layer over the low-k layer, forming at least one opening in the anti-reflective layer and in the low-k layer, forming a nitrogen-free liner in the at least one opening, and forming at least one recess through the nitrogen-free liner, the anti-reflective layer, and at least partially into the low-k layer, the at least one recess is disposed over the at least one opening.