An alignment mark structure includes a dielectric layer. A trench is embedded in the dielectric layer. An alignment mark fills up the trench, wherein the alignment mark includes a metal layer covering the trench. A first material layer covers and contacts the metal layer. A second material layer covers and contacts the first material layer. A third material layer covers and contacts the second material layer. The first material layer, the second material layer, and the third material layer independently includes silicon nitride, silicon oxide, tantalum-containing material, aluminum-containing material, titanium-containing material, or a low-k dielectric having a dielectric constant smaller than 2.7, and a reflectance of the first material layer is larger than a reflectance of the second material layer, the reflectance of the second material layer is larger than a reflectance of the third material layer.