Patent ID: 7992115

Claim:
A method of measuring overlay between a first structure and a second structure on a substrate, said first structure comprising a first plurality of equidistant elements and said second structure comprising a second plurality of equidistant elements, wherein said first plurality of equidistant elements alternate with said second plurality of equidistant elements, and wherein a design width CD 1 of said first plurality of equidistant elements is different from a design width CD 2 of said second plurality of equidistant elements, said method comprising: receiving a plurality of points of interest (x i, y i ) to be investigated on said substrate; determining a double patterning overlay error (DPTO error) between said first structure and said second structure for each point of interest (x i, y i ); measuring, using a metrology tool or scanning electron microscope (SEM), for each point of interest (x i, y i ) a width W 1 of a first element and a width W 2 of a second element; determining for each point of interest (x i, y i ) a difference between said measured width W 1 of said first element and said width W 2 of said second element; determining a distribution of the number of points of interest having approximately the same value for said difference as a function of said difference; and identifying points of interest associated with a sub-distribution as having incorrectly measured overlay errors when said distribution comprises said sub-distribution around a value W 1 -W 2 having an opposite sign as compared to the difference CD 1 -CD 2 .