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.
Beamline for measurement and characterization of multilayer optics for EUV lithography
Currently, intense efforts are in progress to develop a system to print 0.1 micrometers features operating at an extreme UV (EUV) wavelength between 11 and 14 nm. Such a development is critically dependent on the multilayer reflectors which are needed to coat the reflective masks and the optical elements of both the condenser and the projection systems. Understanding of the optical properties of these coatings requires an accurate, well-characterized and stable measurement facility operating over the appropriate wavelength range. This paper describes a beamline installed on a synchrotron radiation source which provides exceptionally high flux, high spectral resolution, absolute wavelength calibration, and excellent higher order suppression in the EUV range. It allows reflectivity measurements to be made to a precision of better than 0.5 percent, determination of wavelength to 0.01 percent, and the measurement of scattering down to 10-10 of the specular beam. The achievement of this performance through the design of the beamline is briefly discussed, and a variety of representative results are presented.
Generation of a parallel X-ray beam and its use for testing collimators
A technique is described, by which a glass strip may be bent to match any curve of large radius of curvature, to a high degree of accuracy, so that it may be used as a glancing incidence X-ray or extreme ultraviolet optical element. The desired match is obtained by applying the optimum combination of end couples and by varying the cross-sectional moment of inertia along the length of the strip. A particular case, that of a parabola for use as a laboratory X-ray collimator, is considered in detail. The analysis predicts that a collimation of one or two arc seconds should be obtainable in practice, with simple and inexpensive apparatus. A prototype collimator to be used for the testing of space payloads using geometric (McGrath) collimators is described and laboratory results presented.