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Increased particle inspection sensitivity by reduction of background scatter variance

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Author: Walle, P. van der · Kumar, P. · Ityaksov, D. · Versluis, R. · Maas, D.J. · Kievit, O. · Janssen, O. · Donck, J.C.J. van der
Source:27th Conference on Metrology, Inspection, and Process Control for Microlithography, 25-28 February 2013, San Jose, CA, USA, 8681
Proceedings of SPIE - The International Society for Optical Engineering
Identifier: 473181
ISBN: 9780819494634
Article number: 868116
Keywords: Electronics · Dark-field microscopy · Detection limit · EUVL · Illumination · Particle inspection · Qualification · Rapid Nano · Speckle · High Tech Systems & Materials · Industrial Innovation · Physics & Electronics · NI - Nano Instrumentation · TS - Technical Sciences


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. © 2013 SPIE.