Browse Prior Art Database

Detecting Microvoids in Materials for Reliability

IP.com Disclosure Number: IPCOM000100735D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 93K

Publishing Venue

IBM

Related People

Arienzo, M: AUTHOR [+2]

Abstract

Disclosed is a detection methodology for identifying microvoids in materials using positron annihilation techniques. Such microvoids may represent the early stages of materials failure, such as can occur in thin film technology, where prominent examples would include electromigration failure in metal interconnects, delamination or adhesion failure, incomplete material filling (seams), barrier layer failure, or material reactions or changes (e.g., diffusion, compound formation). The identification of microvoids as early stages of materials failure may be important for reliability testing and evaluation.

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Detecting Microvoids in Materials for Reliability

       Disclosed is a detection methodology for identifying
microvoids in materials using positron annihilation techniques.  Such
microvoids may represent the early stages of materials failure, such
as can occur in thin film technology, where prominent examples would
include electromigration failure in metal interconnects, delamination
or adhesion failure, incomplete material filling (seams), barrier
layer failure, or material reactions or changes (e.g., diffusion,
compound formation). The identification of microvoids as early stages
of materials failure may be important for reliability testing and
evaluation.

      The physics of positron interactions with solids has been
described in detail in [1].  Positrons - the antiparticles for
electrons, or essentially electrons with positive charge - are
metastable particles generated in nuclear reactions.  They thermalize
quickly in solids, can diffuse up to a few thousand angstroms in some
materials, and decay by annihilation with electrons to emit gamma
rays. The energy and angular distribution of emitted gamma rays is
indicative of the electronic structure in the immediate vicinity of
the annihilation event.  Electron-positron annihilation leads to
emission of 2 gamma rays of about 511 keV each.  In some
circumstances, the positron may form a bound state with an electron -
called positronium - in either the triplet state (spin one,
ortho-positronium) or the singlet state (spin zero,
para-positronium).  The triplet decays into 3 gamma rays, while the
singlet emits 2 gamma rays, like direct positron-electron
annihilation.  In free space the triplet/singlet branching ratio is
3/1, a consequence of spin statistics.  Triplet (3 gamma) vs. singlet
(2 gamma) decay are readily differentiated by coincidence detection
or from the annihilation characteristics (e.g., the energy
distribution of gamma rays).  The triplet lifetime in vacuum (142 ns)
is much longer than the singlet lifetime (125 ps).

      In exploiting positron annihilation techniques for microvoid
detection in thin film materials, three important aspects of positron
interaction with solids must be emphasized.
1.  By varying the incident positron energy in the range 0 to 10 keV,
average positron implantation depths ca...