Patent ID: 8031329

Claim:
A method for forming an overlay mark that is for checking alignment accuracy between a patterned lower layer and an upper layer defined by a lithography process, wherein the lower layer has been subjected to a patterning process, comprising: during the patterning process, forming a first x-directional bar pattern, a first y-directional bar pattern, a second x-directional bar pattern and a second y-directional bar pattern in a portion of the lower layer; and in the lithography process, forming a first x-directional photoresist bar, a first y-directional photoresist bar, a second x-directional photoresist bar and a second y-directional photoresist bar that are located over the portion of the lower layer and surrounded by the bar patterns, wherein at least one of the patterning process and the lithography process includes two exposure steps respectively for defining a first device area and a second device area, when the patterning process includes two exposure steps, the first x-directional bar pattern and the first y-directional bar pattern are defined simultaneously by one of the two exposure steps and the second x-directional bar pattern and the second y-directional bar pattern are defined simultaneously by the other of the two exposure steps, and when the lithography process includes two exposure steps, the first x-directional photoresist bar and the first y-directional photoresist bar are defined simultaneously by one of the two exposure steps and the second x-directional photoresist bar and the second y-directional photoresist bar are defined simultaneously by the other of the two exposure steps.