Patent ID: 7349105

Claim:
A method for measuring an overlay between a first reticle and a second reticle comprising: printing a first pattern of the first reticle onto a substrate; etching the first pattern into the substrate; printing a second pattern of the second reticle onto the substrate, wherein the second pattern partially overlaps the first pattern and the printing the second pattern generates an interference pattern on the substrate; generating a reference mark adjacent to the interference pattern, wherein generating the reference mark comprises: printing a third pattern of the first reticle onto the substrate, wherein the third pattern is adjacent to the first pattern; etching the third pattern into the substrate; and printing a fourth pattern of the second reticle onto the substrate, wherein the fourth pattern is adjacent to the second pattern, wherein the fourth pattern partially overlaps the third pattern to generate a second interference pattern; and measuring a shift in the interference pattern to determine the overlay, wherein measuring the shift in the interference pattern comprises comparing a first position of a first peak of the interference pattern to a second position of a second peak of the second interference pattern.