Patent ID: 7432605

Claim:
An overlay mark for checking alignment accuracy between a lower layer and a lithography process for defining an upper layer, comprising: a part of the lower layer, having two first x-directional trenches, two first y-directional trenches, two second x-directional trenches and two second y-directional trenches therein; and two x-directional photoresist bars and two y-directional photoresist bars formed in the lithography process, over the part of the lower layer and surrounded by the trenches, wherein when the lower layer is fully aligned with the lithography process, an intersection of a central line of the two first x-directional trenches and a central line of the two first y-directional trenches, an intersection of a central line of the two second x-directional trenches and a central line of the two second y-directional trenches and an intersection of a central line of the two x-directional photoresist bars and a central line of the two y-directional photoresist bars coincide with each other.