Characterization of pattern-placement error for sub-40-nm memory devices

Pattern-placement error (PPE) due to lens aberration is characterized for sub-40-nm memory devices. The amount of PPE depends on the feature size. PPE difference between memory cell and traditional box-in-box or advanced imaging metrology marks of KLA-Tencor Corporation is 4nm in the worst case for a given illumination condition. To avoid this kind of problem, a cell-like segmentation may be applied for alignment and overlay marks. However, the cell-like segmentation could degrade the alignment-signal intensity. In this article, a simple but effective methodology is introduced so that optimum segmentation size is determined. As a result, PPE error of alignment/overlay marks is close to memory cells with enough alignment-signal intensity.