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Highly Sensitive Particle Detection

IP.com Disclosure Number: IPCOM000116944D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

Disclosed is a particle detection apparatus for measuring the light scattered from particles, the detection apparatus having a condensor with increased inner and outer aperture due to deionized water used as immersion fluid for the condensor. This allows to illuminate particles by locally suppressed total reflexion.

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Highly Sensitive Particle Detection

      Disclosed is a particle detection apparatus for measuring the
light scattered from particles, the detection apparatus having a
condensor with increased inner and outer aperture due to deionized
water used as immersion fluid for the condensor.  This allows to
illuminate particles by locally suppressed total reflexion.

      To assure that the masks used for semiconductor manufacturing
are free of defects, known measuring methods are using the light
scattered from particles, methods which today allow to detect
particles of 0.8 &mu.m in diameter on chromium masks.  In future
products like the 1 GBit chip particles of diameters down to 150 nm
have to be detected.  It becomes more and more difficult to
distinguish between particles and the edges of the mask pattern which
are also scattering and diffracting light.  Small particles scatter
with 1/&lambda.3  where &lambda.  is the wavelenght of the
illuminating laser source.  The prices for lasers of short
wavelengths increase and therefore it is desirable to find a method
which allows to detect small particles with laser sources having the
longest possible wavelengths.

      The numerical aperture N.A.  =  n sin &alpha.  (with n being
the refractive index and &alpha.  being the angle of incidence).  The
use of immersions with n >  1 increases the numerical aperture.
Deionized water of highest purity and with n =  1.33 may be used as
immersion fluid for a darkfie...