Embodiments of the present disclosure provide an apparatus and methods for forming stair-like structures with accurate profiles and dimension control for manufacturing three dimensional (3D) stacked semiconductor devices. In one embodiment, a method of forming stair-like structures on a substrate includes forming a film stack including a dielectric layer and a ruthenium containing material, and etching the ruthenium containing material in the film stack exposed by a patterned photoresist layer utilizing a first etching gas mixture comprising an oxygen containing gas.