Actinic Mask Blank Inspection and Signal Analysis for Detecting Phase Defects Down to 1.5 nm in Height

Abstract

The capability of an actinic (at-wavelength) inspection system for extreme ultraviolet lithography (EUVL) mask blank has been analyzed by experiment and simulation. The actinic inspection optics, that we developed to obtain a two-dimensional dark field image, consists of illumination optics, Schwarzschild optics with concave and convex mirrors as dark-field imaging optics, and a back-illuminated chargecoupled-device (BI-CCD). A test mask blank with programmed bump defects of smaller sizes and lower heights compared to those used in a previous work was fabricated and the bump defects were detected by the tool. The inspection experiments demonstrated that fabricated multilayer defects down to 1.5 nm in top height and 60 nm in width can be successfully detected. The simulation further indicated that the inspection optics performed well in detecting phase defects of 1.5 nm in height and 40 nm in width.

Defect inspection with an EUV microscope

“…The deflection mirror also acts as a zero order stop for the specular beam enabling dark field operation by shadowing the directly reflected EUV beam. Due to increased contrast dark field operation is preferred [4,5].…”

Phase defect characterization on an extreme-ultraviolet blank mask using microcoherent extreme-ultraviolet scatterometry microscope

“…The EUVL Infrastructure Development Center (EIDEC) groups have developed an actinic blank inspection (ABI) tool to detect phase defects. [7][8][9][10] The ABI tool is a dark-field EUV microscope, composed of a discharge-produced-plasma source and Schwarzschild optics, which collects the scattered EUV light from buried defects to form a dark-field image on a charge-coupled-device (CCD) camera. Because the defect signal is integrated into a dark-field, the ABI tool has a good signal-to-noise (S/N) ratio for defect detection.…”

Analytical and experimental evaluation of a counting method for particles added during the mask handling process

“…1-3 Some issues concern mask technologies such as mask cleaning, 4 mask protection techniques, 5 defect-free mask fabrication, 6,7 and particle-free mask handling techniques. However, many issues need to be resolved before the practical use of EUVL.…”

“…1-3 Some issues concern mask technologies such as mask cleaning, 4 mask protection techniques, 5 defect-free mask fabrication, 6,7 and particle-free mask handling techniques. 6,7 Similarly, the decrease in particles should be examined in developing mask-cleaning techniques. For example, the increase in particles or defects should be examined in developing particle-free mask handling techniques, [8][9][10][11][12][13][14][15] and defect-free mask fabrication.…”