Actinic defect counting statistics over 1-cm2 area of EUVL mask blank
As a continuation of comparison experiments between EUV inspection and visible inspection of defects on EUVL mask blanks, we report on the result of an experiment where the EUV defect inspection tool is used to perform at-wavelength defect counting over 1 cm2 of EUVL mask blank. Initial EUV inspection found five defects over the scanned area and the subsequent optical scattering inspection was able to detect all of the five defects. Therefore, if there are any defects that are only detectable by EUV inspection, the density is lower than the order of unity per cm2. An upgrade path to substantially increase the overall throughput of the EUV inspection system is also identified in the manuscript.
High sensitivity actinic detection of native defects on extreme ultraviolet lithography mask blanks
We present recent experimental results of actinic extreme ultraviolet lithography mask blank defect inspection. The detection sensitivity of the current actinic inspection system is predicted to be able to reach approximately 30 nm in cross correlation experiments done with commercial visible-light, scanning electron microscopy (SEM), and atomic force microscopy (AFM) inspection tools. Random, native defects identified using the visible-light tool were scanned by the actinic tool and the scattering characteristics were compared. SEM and AFM characterization of selected defects were also performed for physical measurement. We found a defect whose size was as small as 60 nm and AFM analysis showed that this defect was a 3 nm high substrate defect that was smoothed-out by the multilayer coating.
Mask blanks for extreme ultraviolet lithography: Ion beam sputter deposition of low defect density Mo/Si multilayers
We report on the growth of low defect density Mo/Si multilayer (ML) coatings. The coatings were grown in a deposition system specifically designed for extreme ultraviolet lithography mask blank fabrication. Complete, 81 layer, high reflectance Mo/Si ML coatings were deposited on 150 mm diam (100) oriented Si wafer substrates using ion beam sputter deposition. Process added defect densities correspond to 2×10−2/cm−2 larger than 0.13 μm as measured by optical scattering. This represents a reduction in defect density of Mo/Si ML coatings by a factor of 105.