An overlay mark for checking alignment accuracy between a former layer and a later layer on a wafer is described, including a former pattern as a part of the former layer, and a later pattern as a part of a patterned photoresist layer defining the later layer. The former pattern has two parallel opposite edges each forming a sharp angle α with the x-axis of the wafer. The later pattern also has two parallel opposite edges each forming the sharp angle α with the x-axis of the wafer.