Our work

Detection of ≤10 nm particles

Contamination of masks and wafers by particles have been an issue in lithography systems from the beginning. With the reduction in the dimensions of the structures on the masks over the years, avoiding the presence of smaller particles became relevant. For the near future particles of 10 nm and smaller become relevant on masks being used  in the EUV scanners. Currently no tooling exists to reliably scan the unpatterned blanks during mask production on the presence of particles smaller than 20 nm, in a reasonable amount of time.

We have studied the benefit of using soft  X-ray wavelengths (10-40 nm) and the benefit to use phase information compared to the current use of intensity information. The conclusion was that using phase information only helps when the roughness of the substrate is more than being found in practice.

The use of soft X-ray wavelengths increases the relative measurement signal from a particle. The maximum gain however is limited by the increased transparency of particles at shorter wavelengths. The main parameter in the measurement time is the available source power. The non-coherent EUV sources that have been developed as source for the EUV scanners now have the potential to provide enough photons.


The use of a non coherent EUV source to scan blanks for ≤10 nm particles has the benefit of the improved contrast of the small particles, enabling to reduce the lower limit in particle sizes that can be detected, compared to the current systems operating at a wavelength of 193 nm.


  • Qualification of unpatterned blanks for EUV masks during production in order to prevent particles buried under the multilayer stack.
  • Scanning of witness samples on the presence of particles in order to qualify the cleanliness of semicon equipment.


No tests have been performed, but could be scheduled when a new high power EUV source becomes available at TNO as part  of the EBL2 test set-up.


Detection of 10 nm PSL particles on a smooth silicon surface (150 × 150 mm), with less than 1% particles missed and less than 10 false positives. This all within half a day.


Dr Stefan Bäumer

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

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