Probing limits of acoustic nanometrology using coherent extreme ultraviolet light

Photoacoustic nanometrology using coherent extreme ultraviolet (EUV) light detection is a unique and powerful tool for probing ultrathin films with a wide range of mechanical properties and thicknesses well under 100 nm. In this technique, short wavelength acoustic waves are generated through laser excitation of a nano-patterned metallic grating, and then probed by diffracting coherent EUV beams from the dynamic surface deformation. Both longitudinal and surface acoustic waves within thin films and metallic nanostructures can be observed using EUV light as a phase-sensitive probe. The use of nanostructured metal transducers enables the generation of particularly short wavelength surface acoustic waves, which truly confine the measurement within the ultrathin film layer of interest, to thicknesses < 50 nm for the first time. Simultaneous measurement of longitudinal and transverse surface wave velocities yields both the Young’s modulus and Poisson’s ratio of the film. In the future, this approach will make possible precise mechanical characterization of nanostructured systems at sub-10 nm length scales.

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