Ionization Mass Spectroscopy (LIMS)
Ionization Mass Spectroscopy (LIMS) is a relatively new failure analysis technique used in
the compositional analysis of a sample.
LIMS operates by removing
ions from the sample using a microfocused high-power density laser beam,
and then analyzing the mass of these ions. The removal of material
for analysis is accomplished in one of two laser irradiation modes: 1)
by laser desorption (LD); and 2)
by laser ionization (LI).
Once the ions
are removed from the sample either by LD or LI, the ions are subjected to
analysis using a mass spectrometer of time-of-flight design, wherein the
mass values of the ions are quantified based on their transit time across
a high vacuum region through which they are accelerated by an electric
field of known value.
produces ions from the specimen during the vaporization of the material
with the laser beam. LI therefore operates under high irradiance
levels of more than 1010 W/cm2, and can sample well
into the bulk of the specimen. For instance, LI analysis can sample
depths on the order of 1000 to 2000 angstroms per laser shot for GaP.
On the other
hand, laser desorption can only produce ions from the specimen surface or
from substances that are adsorbed on the specimen surface because it
operates under relatively low irradiance levels of less than
LD sampling depths are on the order of 100 to 200 angstroms per laser
applications of LIMS as a microanalytical tool include: 1) bulk
microanalysis of conductor and insulator materials; 2) surface analysis of
thin films, contamination, and adsorbed elements and molecules.
advantages offered by LIMS is its high elemental sensitivity, wide mass
analysis range, and relatively small beam diameter (1 to 5 microns).
Because of these, LIMS can distinguish between the bulk material,
the materials that are just adsorbed on the surface of the specimen, and
materials incorporated in a matrix.
FA Techniques; SIMS;
ESCA or XPS; FTIR Spectroscopy;
Equipment; Basic FA
Package Failures; Die
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