GHz half wavelength contact acoustic microscopy (HaWaCAM): A feasibility study

B. A.J. Quesson*, P. L.M.J. Van Neer, M. S. Tamer, K. Hatakeyama, M. H. Van Es, M. C.J.M. Van Riel, D. Piras

*Corresponding author for this work

Research output: Contribution to journalConference articleScientificpeer-review

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The semiconductor industry needs to fit ever more devices per unit area to improve their performance; hence a trend towards increasingly complex structures by varying material combinations and 3D geometries with increasing aspect ratios. The new materials used may be optically opaque, posing problems for traditional optical metrology methods. One solution is to use acoustical waves, which present the double advantage of not being hampered by optically opaque layers and allowing for penetration depths of 10's of μm at sub-μm wavelengths; which is considerably larger than most traditional optical methods (O(100 nm's - μm's)). Here, we present a novel acoustic metrology method using GHz ultrasound waves to measure deeply buried subsurface features (>5 μm). The concept consisted of a GHz acoustic transducer integrated above the tip of a custom designed probe, which is then scanned across a sample. The method uses non-damaging solid-solid contact without the need for liquid coupling layers - in contrast to conventional acoustical microscopy. This allows for the use of much higher acoustic frequencies, hence higher on-axis resolutions. The transducer is used in pulse-echo mode and a stage controller is used to move the probe for scanning. An experimental setup was built with a 4 GHz transducer and tested successfully on 1.5-2 μm size features buried below a 5 μm PMMA or 10 μm SiO2layer, respectively. A good match was further obtained between the measurements and the model predictions. These results demonstrated the feasibility of the new method, opening new opportunities for metrology and inspection applications.

Original languageEnglish
Number of pages7
JournalProceedings of SPIE - The International Society for Optical Engineering
Publication statusPublished - 2022
EventMetrology, Inspection, and Process Control XXXVI 2022 - Virtual, Online
Duration: 23 May 202227 May 2022

Bibliographical note

Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project
Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


  • acoustic metrology
  • GHz acoustic metrology
  • half wavelength contact area
  • half-wavelength contact acoustic microscopy
  • HaWaCAM
  • solid contact


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