A multi-layer reflective structure is disposed over the substrate. An amorphous capping layer is disposed over the multi-layer reflective structure. The amorphous capping layer may contain ruthenium, oxygen, niobium, nitrogen, tantalum, or zirconium. An amorphous layer may also be disposed between the multi-layer reflective structure and the amorphous capping layer. The amorphous layer includes amorphous silicon, amorphous silicon oxide, or amorphous silicon nitride.