Actinic inspection of extreme ultraviolet programed multilayer defects and cross-comparison measurements

Abstract

High sensitivity actinic detection of native defects on extreme ultraviolet lithography mask blanksThe production of defect-free mask blanks remains a key challenge for extreme ultraviolet ͑EUV͒ lithography. Integral to this effort is the development and characterization of mask inspection tools that are sensitive enough to detect critical defects with high confidence. Using a single programed-defect mask with a range of buried bump-type defects, the authors report a comparison of measurements made in four different mask inspection tools: one commercial tool using 488 nm wavelength illumination, one prototype tool that uses 266 nm illumination, and two noncommercial EUV "actinic" inspection tools. The EUV tools include a dark field imaging microscope and a scanning microscope. Their measurements show improving sensitivity with the shorter wavelength non-EUV tool, down to 33 nm spherical-equivalent-volume diameter, for defects of this type. Measurements conditions were unique to each tool, with the EUV tools operating at a much slower inspection rate. Several defects observed with EUV inspection were below the detection threshold of the non-EUV tools.

EUV and non-EUV inspection of reticle defect repair sites

“…We have developed a unique actinic mask inspection tool 1,2 that operates at EUV wavelengths and is now used in the evaluation of patterned and open-field defect repair strategies without printing 3,4 . The tool is also being used to deepen our understanding of the sensitivity of non-actinic inspection methods, and to resolve research questions about the development of, or need for, commercial actinic tools 3,5 .…”

Evaluation of extreme-ultraviolet lithography mask absorber pattern on multilayer phase defect using extreme-ultraviolet microscope

“…Inc. and the EUV dark-field actinic-inspection system at MIRAI and LBNL, can also detect these phase defects. 6,7 However, the detection principles on which they are based do not permit an aerial image of the mask absorber pattern to be produced.…”

Background level in extreme-UV dark-field image for mask blank inspection

“…When particles or pits are buried in the multilayer, resulting in very small protrusions or depressions on the multilayer surface, the defects produced in such cases are hardly noticeable using a conventional inspection tool with a deep-UV wavelength. Therefore, an actinic (at the wavelength of wafer exposure) blank inspection (ABI) technique is being developed [1][2][3][4][5][6].…”