Multi-patterning overlay control

The extension of optical lithography to 32nm and beyond is dependent on double-patterning (DP) at critical levels. DP integration strategies result in added degrees of freedom for overlay variation. In particular, overlay control requires assessment of error among various mask/level combinations. The Blossom overlay metrology approach minimizes the size of the overlay marks associated with each mask/level while maximizing the density of marks within the overlay metrology tool's field of view (FOV). We examine Blossom enabled use cases in DP lithography control; specifically, within-field and multiple mask/level sampling.