Increased particle inspection sensitivity by reduction of background scatter variance

Peter Van Der Walle, Pragati Kumar, Dmitry Ityaksov, Richard Versluis, Diederik J. Maas, Olaf Kievit, Ochem Janssen, Jacques C.J. Van Der Donck

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

Abstract

In dark-field particle inspection, the limiting factor for sensitivity is the amount of background scatter due to substrate roughness. This scatter forms a speckle pattern and shows an intensity distribution with a long tail. To reduce false-positives to an acceptable level, a high detection threshold should be chosen such that the tail of the background distribution is avoided. We have modeled an optimized illumination mode, that reduces the variance in the background distribution. This illumination mode illuminates the substrate from multiple azimuth angles. We show that the speckle patterns generated by each azimuth angle can be independent from each other. Therefore by combining the angles, the variance of the background signal is reduced. We show that for the parameters of our inspection system the detection threshold can be reduced by a factor three, resulting in a lower detection limit that is 20% smaller in particle size. The change in the background scattering distribution was confirmed by experiments.

Original languageEnglish
Title of host publicationMetrology, Inspection, and Process Control for Microlithography XXVII
DOIs
Publication statusPublished - 2013
Event27th Conference on Metrology, Inspection, and Process Control for Microlithography - San Jose, CA, United States
Duration: 25 Feb 201328 Feb 2013

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume8681
ISSN (Print)0277-786X

Conference

Conference27th Conference on Metrology, Inspection, and Process Control for Microlithography
Country/TerritoryUnited States
CitySan Jose, CA
Period25/02/1328/02/13

Keywords

  • Dark-field microscopy
  • Detection limit
  • EUVL
  • Illumination
  • Particle inspection
  • Qualification
  • Rapid Nano
  • Speckle

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