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 at NIST. It was given an R&D 100 Award in 2010. 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 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.
^Attota, R.; Bunday, B.; Vartanian, V. (2013). "Critical dimension metrology by through-focus scanning optical microscopy beyond the 22 nm node". Appl. Phys. Lett. 102 (22): 222107. doi:10.1063/1.4809512.
^Attota, R.; Dixson, R.G. (2014). "Resolving three-dimensional shape of sub-50 nm wide lines with nanometer-scale sensitivity using conventional optical microscopes". Appl. Phys. Lett. 105: 043101. doi:10.1063/1.4891676.
^Attota, R.; Kavuri, P.P.; Kang, H.; Kasica, R.; Chen, L. (2014). "Nanoparticle size determination using optical microscopes". Appl. Phys. Lett. 105 (16): 163105. doi:10.1063/1.4900484.
^Kang, H.; Attota, R.; Tondare, V.; Vladar, A.E.; Kavuri, P. (2015). "A method to determine the number of nanoparticles in a cluster using conventional optical microscopes". Appl. Phys. Lett. 107 (10): 103106. doi:10.1063/1.4930994.