Patent ID: 7629259

Claim:
A method, comprising: forming a first patterned layer with a first alignment grid; forming sidewall layers over the first patterned layer to perform a first shrink; etching the first alignment grid after shrink into an etch layer to form an etched first alignment grid, wherein the etched first alignment grid comprises: a first line with a length and a width, wherein the length is at least four times greater than the width; a second line substantially parallel to and spaced apart from the first line to form a first space between the first line and the second line; a third line with a length and width, wherein the length is at least four times greater than the width, and wherein the third line is perpendicular to the first line; and a fourth line substantially parallel to and spaced apart from the third line; removing the patterned layer; measuring an optical pattern of a second alignment grid aligned over the etched first alignment grid; and using the optical pattern to determine whether the second alignment grid is aligned over the etched first alignment grid.