NEW TEST STRUCTURE FOR NANOMETER-LEVEL OVERLAY AND FEATURE-PLACEMENT METROLOGY

A new electrical test structure for overlay measurement has been evalu ated by replicating arrays of its complementary components from two di fferent photomasks into a conducting film on a quartz substrate. The f eatures resulting from images projected from the first mask were used as a reference grid which was calibrated by the NIST line-scale interf erometer. A first subset of the relative placements of the images proj ected from the second mask, which were derived from the electrical ove rlay measurements and the reference grid, agreed to within 13 nm with corresponding measurements made directly by the line-scale interferome ter over distances up to 13.5 mm. A second comparison made at another substrate location indicated that gradients of projected feature linew idths across the exposure site may need to be measured, and corrected for, in the electrical extraction of overlay.