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Non-Contacting Techniques for Sample Charging in Electron Beam Inspection Or Testing Apparatus

IP.com Disclosure Number: IPCOM000120662D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 4 page(s) / 185K

Publishing Venue

IBM

Related People

Chang, TP: AUTHOR [+4]

Abstract

Compact arrangements are described for electron beam irradiation of a large area, individual subareas or individual details on the back side of a sample, such as a multilayer ceramic wiring module. In one arrangement a photocathode is combined with a multi-channel electron multiplier. The photocathode is irradiated with light from an external source (flooded or scanned) or from an adjacent laser diode array. In another arrangement, an array of individual electron sources are used, each having focussing optics and a deflector.

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Non-Contacting Techniques for Sample Charging in Electron Beam Inspection
Or Testing Apparatus

      Compact arrangements are described for electron beam
irradiation of a large area, individual subareas or individual
details on the back side of a sample, such as a multilayer ceramic
wiring module.  In one arrangement a photocathode is combined with a
multi-channel electron multiplier.  The photocathode is irradiated
with light from an external source (flooded or scanned) or from an
adjacent laser diode array.  In another arrangement, an array of
individual electron sources are used, each having focussing optics
and a deflector.

      Some electron beam inspection and testing techniques require
the charging of the back side of a sample in-situ with an electron
beam (see, for example, -1-).  Depending on the test procedure, it is
desired to charge either the whole back side or selected areas or
only selected details.  The charging must be done either to a
positive or a negative potential relative to ground.  Usually, there
are severe space limitations for the charging apparatus because the
specimen is in a vacuum chamber and in most cases on top of an x-y
table.  Arrangements are described which are compact in size and
which allow for either flood beam, selected area, or selected detail
charging to either positive or negative potentials.

      Some electron beam inspection techniques are based on detection
of voltage contrast.  A potential is applied to circuit details under
inspection.  This is achieved without making mechanical contact to
the sample by irradiating the region to be charged with electrons of
an energy for which the yield of secondary and backscattered
electrons is different from 100%.  Depending upon the material to be
charged, the energy of the incoming electrons must be in the range of
from several hundred to several thousand electron volts.  If the
secondary electron yield is smaller than 100%, the irradiated area
becomes charged to a negative potential.  If the secondary electron
yield is larger than 100%, it is charged to either a positive or a
negative potential depending upon the potential applied to a charge
stabilizer grid in front of the irradiated surface.

      The lateral dimensions of the samples can be quite large,
typically 4 inches.  In order to spread a beam emerging from a single
source over this area or to scan across it, space normal to the
sample of about once or twice the sample dimensions is required.
Since all this must be accomplished inside the evacuated specimen
chamber of the inspection machine, there are severe spatial
restrictions.

      In Fig. 1, a photo-cathode 10 as large as the biggest sample 12
to be inspected is used as an electron source. This photo-cathode may
consist of a high photo-electron yield film 14 (Pd and CsI are
examples) on a transparent substrate 16.  Film 14 may be homogeneous
or consist of an array of individual islands.  An array may...