Our work

Quantitative phase imaging: 3D Nano-imaging

In the industry there is a need for metrology instruments that are capable of accurately measuring the three-dimensional shape of nanometre sized objects. In a quantitative phase imaging (QPI) instrument such three-dimensional shape information is obtained by measuring the phase of electro magnetic radiation (‘light’) that has been reflected from the object under test, and subsequently (numerical) reconstruction of the object’s geometry.

Furthermore, a set of QPI techniques (such as ptychography and digital holography) allows for ‘lens less imaging’. Aside from potential cost- and volume benefits, lens less imaging concepts also allow for the use of shorter wavelength radiation for which no (practical) lenses or curved mirrors exist.


Enabling the practical use of extreme ultraviolet radiation (EUV) for high-numerical aperture imaging, allows for a significant improvement of the attainable resolution compared to more traditional optical methods.

Enabling the practical use of EUV radiation for high-numerical aperture imaging, allows for non-contact 3D metrology.


Three-dimensional metrology of Fin-FET structures for semicon.


Within the ERP we have identified currently existing sources, measurement methods and reconstruction algorithms. By numerical modelling of a QPI 3D nano imaging system we have identified the major challenges that need to be addressed before the technology can be applied in industry.

These challenges are (a) improvement of coherent EUV source power by various orders to realise competitive through-puts; and (b) improved reconstruction algorithms including the 3D volume interaction between the object and the incident and scattered EUV radiation.

Since these challenges do not match unique TNO expertise, it has been decided to no longer pursue the development of a QPI-based 3D nano-imaging instrument.


  • A resolution in three dimensions of 20 nm with the prospect for improvements down to 10 nm.
  • The measurement time for a 10 × 10 µm area should be less than 25 sec (ITRS roadmap 2017).

Dr Stefan Bäumer

  • optics
  • System architecture
  • Optical design
  • Optical Metrology
  • Micro- optics

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