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Through-Focus Scanning Optical Microscopy (TSOM) is an imaging method that produces nanometer-scale three-dimensional measurement sensitivity using a conventional bright-field optical microscope. TSOM has been introduced and maintained by Ravikiran Attota[1] at NIST. It was given an R&D 100 Award in 2010.[2] In the TSOM method a target is scanned through the focus of an optical microscope, acquiring conventional optical images at different focal positions. The TSOM images are constructed using the through-focus optical images. A TSOM image is unique under given experimental conditions and is sensitive to changes in the dimensions of a target in a distinct way, which is very well applicable in nanoscale dimensional metrology. The TSOM method is alleged to have several nanometrology[3][4][5][6][7] applications ranging form nanoparticles to through-silicon-vias (TSV).

The National Institute of Standards and Technology, USA, produced a short Video on YouTube on the TSOM method.


  1. ^ http://www.nist.gov/pml/div683/grp03/rattota.cfm
  2. ^ http://www.rdmag.com/Awards/RD-100-Awards/2010/08/Bringing-out-of-focus-into-the-picture/
  3. ^ http://www.nist.gov/pml/div683/grp03/upload/tsom-ravikiran-attota.pdf
  4. ^ Ravikiran Attota, Ronald G. Dixson and Andras E. Vladár " Through-focus scanning optical microscopy ", Proc. SPIE 8036, Scanning Microscopies 2011: Advanced Microscopy Technologies for Defense, Homeland Security, Forensic, Life, Environmental, and Industrial Sciences, 803610 (June 1, 2011); http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1265236 doi:10.1117/12.884706
  5. ^ R. Attota, B. Bunday, V. Vartanian, "Critical dimension metrology by through-focus scanning optical microscopy beyond the 22 nm node," Appl. Phys. Lett., 102 (22), 222107 (2013). http://dx.doi.org/10.1063/1.4809512
  6. ^ R. Attota and R.G. Dixson. Resolving three-dimensional shape of sub-50 nm wide lines with nanometer-scale sensitivity using conventional optical microscopes. Appl. Phys. Lett., 105, 043101, July 29, 2014, http://dx.doi.org/10.1063/1.4891676.
  7. ^ R. Attota, P.P. Kavuri, H. Kang, R. Kasica, L. Chen, "Nanoparticle size determination using optical microscopes," Appl. Phys. Lett., 105 (16), 163105, (2014). http://dx.doi.org/10.1063/1.4900484