Antireflection mask for contact hole opening

An antireflection mask and method of using the antireflection mask to form contact holes for an integrated circuit wafer are described. The antireflection mask has a patterned opaque layer formed on a transparent mask substrate. The patterned opaque layer has first openings for exposing photoresist in regions where the photoresist is thicker and second openings for exposing photoresist in regions where the photoresist is thinner. A patterned layer of antireflection material having a light transmittance of less than 100% is formed over the second openings but not over the first openings. Light is passed through the mask to expose a layer of photoresist. The light exposing the thinner photoresist regions is attenuated by the antireflection material thereby compensating for variations in photoresist thickness. In addition the antireflection material reduces reflections from the patterned opaque layer of the mask.