Nanoscale extreme ultraviolet imaging

Microscopes enhance our capabilities to ‘see’ objects of micron size dimensions.   The resolving capability of a microscope depends on the wavelength of the illumination.  We have developed microscopes that use radiation with wavelengths in the range 13-47 nm for illumination.   These short wavelengths have allowed these microscopes to image nanoscale structures on surfaces.   The high peak power of the extreme ultraviolet laser output enables to capture images with a single shot.  In combination, the microscopes can take sequential images that map dynamic phenomena. 

46.9 nm Microscope

The microscope schematically shown in Fig. 1 uses the output of a compact 46.9 nm laser for illumination.   This microscope was used to image carbon nanotubes with single laser shot at wavelength resolution (Fig. 2).  Its capability for single shot imaging enabled the microscope to follow the repetitive motion of a cantilever oscillating at tens of kHz repetition rate (Fig. 2).  This microscope can also operate in reflection configuration making it possible to image nanopatterns on surfaces. 

Aerial Mask Inspection at 13.2 nm

Extreme ultraviolet Lithography (EUVL) recently deployed at Samsung to  print 7 nm critical dimensions in integrated circuits uses a 13.5 nm incoherent printing system. The masks that are used to print the nanometer scale features need to be free of defects. These masks contain features that are fabricated on Mo/Si multilayer stacks which have a reflectivity  of about 70% at a center wavelength of 13.5 nm. Broad area microscopes can be used to identify defects on the masks. Such a microscope implemented using 13.2 nm laser illumination is shown schematically in the figure.  Its geometry is designed to match the illumination of the masks as it is done in the stepper.   Using this microscope we inspected EUV lithography masks, and got images as shown in Fig. 2, from which quality parameters of the patterns, such as the line edge roughness were obtained. 

Holographic Imaging Microscopy

 We implemented this imaging modality using the 46.9 nm capillary discharge laser, as shown in Fig. 5.   This microscope requires a reference beam and an illuminating object beam which were created using a zone plate.  The object and reference beam create an interference pattern on the 2D array detector that contains information on the phase and contrast of the illuminated object.   This is a powerful methodology for imaging at EUV wavelengths because the absorption contrast between materials is very small.   

Selected Publications 

  • G. Vaschenko, F. Brizuela, C. Brewer, Y. Wang, M.A. Larotonda, B.M. Luther, M.C. Marconi, J.J. Rocca, C.S. Menoni, E.H. Anderson, W. Chao, B.D. Harteneck, J.A. Liddle, Y. Liu, and D.T. Attwood, “Sub-38 nm resolution tabletop microscopy with 13 nm wavelength laser light”, Optics Letters 31, 1214, (2006).
  • Brizuela, S. Carbajo, A. Sakdinawat, D. Alessi, D. H. Martz, Y. Wang, B. Luther, K. A. Goldberg, I. Mochi, D. T. Attwood, B. La Fontaine, J. J. Rocca, and C. S. Menoni, “Extreme ultraviolet laser-based table-top aerial image metrology of lithographic masks,” Opt. Express 18, 14467-14473 (2010).
  • S. Carbajo, I. Howlett, F. Brizuela, K. S. Buchanan, M. C. Marconi, W. Chao, E. H. Anderson, I. Artioukov, A. Vinogradov, J.J. Rocca, and C.S. Menoni, “Sequential single-shot imaging of nanoscale dynamic interactions with a table-top soft x-ray laser,“ Opt. Letters, 37,  pp. 2994-2996 (2012).
  • Nejdl; ID Howlett; D. Carlton; E.H. Anderson; W. Chao; M.C. Marconi; J.J. Rocca; C.S. Menoni, “Image Plane Holographic Microscopy With a Table-Top Soft X-Ray Laser,”  IEEE Photonics Journal 7 (1); Article Number: 6900108, (2015). DOI: 10.1109/JPHOT.2015.2389957.


National Science Foundation, Extreme Ultraviolet Science and Technology Center