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Secondary Electron Crossover Matching for Electron-Beam Testing by Thin Layer Deposition

IP.com Disclosure Number: IPCOM000102659D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 128K

Publishing Venue

IBM

Related People

Brunner, M: AUTHOR [+5]

Abstract

In methods for contactless electron beam (E-beam) testing of interconnection substrates for integrated circuits and/or for testing integrated circuits themselves, wherein an electron beam is used firstly to selectively charge areas on a surface and then is used secondly to detect voltage levels on the surface resulting therefrom, the surface may be coated with a temporary thin layer of material in order to make the electron absorption and emission characteristics of different surface materials more uniform.

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Secondary Electron Crossover Matching for Electron-Beam Testing by Thin Layer Deposition

       In methods for contactless electron beam (E-beam) testing
of interconnection substrates for integrated circuits and/or for
testing integrated circuits themselves, wherein an electron beam is
used firstly to selectively charge areas on a surface and then is
used secondly to detect voltage levels on the surface resulting
therefrom, the surface may be coated with a temporary thin layer of
material in order to make the electron absorption and emission
characteristics of different surface materials more uniform.

      Electron beam testing system allows contactless testing of
shorts and opens on ceramic modules by depositing charge into a
metallic pad of a network with an electron beam and then reading the
charge at all other pads of the network with the same electron beam
of different energy in a voltage contrast mode.  The choice of beam
energy for charging and reading depends on the properties of the
conductors and insulators comprising the substrate.  For our
discussion we will consider the insulator to be ceramic of the type
used in the thermal conduction module and the conductor to be
molydenum or gold.  However, the general principles apply to all
insulators and conductors which might be used to form a substrate.

      In the charging mode, negative charge is deposited by using
primary electron (PE) energies larger than the second crossover E2 in
the secondary electron (SE) yield curve (see the figure) of the
metal.  Ideally for reading, the primary beam energy (PE) is chosen
to be the energy at the second crossover of the metal, where the
number of SEs plus backscattered electrons (BSEs) equals the number
of primary electrons resulting in negligible charging.  In practice
one must also consider the secondary electron yield curve of the
ceramic (or other) insulator when choosing the read and charge
voltages.  With present substrates the ceramic must be scanned to
locate the registration marks on the sample. One of the beam voltages
must be chosen to lie in the range between E1 and E2 (see the figure)
for the ceramic so that it does not charge significantly during
registration.  The voltage difference between read and charge has to
be switched in at high speed.  The electronics of the high voltage
switch and the electron optical problems of maintaining a well
focussed beam at both potentials are significant technical problems
which presently limit the difference between read and charge to 2KV.

      Summarizing the above discussion, substrate materials and
technical limitations impose certain requirements on the charging and
reading beam energies, VC and VR, respectively.
1.  VC > E2 metal
2.  VR < E2 metal
3.  E1 ceramic < VR < E2 ceramic
4.  VC - VR & 2KV

      These conditions are fulfilled for materia...