Printability of substrate and absorber defects on extreme ultraviolet lithographic masks

Abstract

Extreme ultraviolet lithography (EUVL) is a candidate for high-volume production of integrated circuits with 0.1 μm design rules. As a reduction imaging technique with robust mask substrates, EUVL reduces the mask contribution to the critical dimension (CD) error budget. However, the ability to manufacture EUVL mask blanks that are free of printable defects remains an important challenge. Electromagnetic simulations and imaging experiments have suggested that defects in the substrates and reflective coatings, in particular, may be highly printable and difficult to detect. A defect printability study using programmed defects was performed in order to determine the printing behavior of mask defects of different sizes and locations with respect to absorber features. Imaging was performed using a 10× Schwarzschild camera operating at 13.4 nm with a numerical aperture of 0.08, corresponding to a Rayleigh resolution of 0.1 μm. This system has an effective exposure field of 0.4 mm diam. Measurements of the defect-induced linewidth variations on the printed resist lines were performed with scanning electron microscopy and atomic force microscopy. Results show that defects located on the substrate and overcoated by the reflective coating are more printable compared to defects of the same sizes located above the reflective coating. In addition, defects centered in the clear region of lines-and-space (L/S) pattern are more printable compared to those located at the line edge programmed defects located in L/S patterns that are larger than 1/3 of the linewidth caused ≥10% CD variations, while defects that are ≤1/6 of the linewidth did not cause measurable CD variations.