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ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 19 NO. 2
22
ADVANTAGES AND CHALLENGES OF 3-D ATOM PROBE
TOMOGRAPHY CHARACTERIZATION OF FinFETs
Andrew J. Martin, Ajay Kumar Kambham, and Ahmad D. Katnani
GLOBALFOUNDRIES, Inc., Malta, N.Y.
EDFAAO (2017) 2:22-30 1537-0755/$19.00 ©ASM International®
INTRODUCTION
Atomprobe tomography (APT) is a three-dimensional
(3-D) characterization technique that is rapidly expand-
ing its area of influence from primarily metals to include
a plethora of fields ranging from semiconductor devices
and thin films[1-3] to bulk oxides[4] and geological sciences
(including meteorites!)[5] and even to biological materi-
als.[6] Due to its unique nature, APT thrives at producing
first-of-a-kind analysis, assisting in development of new
materials or structures, and identifyingmaterial response
to external forces.[7] Atom probe tomography is of high
interest due to its capability toprovide both structural and
chemical analysis of buried features fromany desired per-
spective with subnanometer resolution[8,9] and all within
the same volume. This is particularly advantageous when
complex 3-D features cloud one’s ability to provide the
necessary analysis using other analytical techniques or
when advancedmodeling is required for proper interpre-
tation. Examples of such situations include quantum dot
dissociation,[10] nanocluster/nanoparticle formation,[11]
dissolution of alloy or dopant constituents at dislocations
and grain boundaries,[7] and dopant distributions in 3-D
semiconductor devices.[1,3] These advantages of APTmake
it a powerful tool for failure analysis and research and
development of the next-generation technologies.
Atom probe tomography is a destructive technique
that relies on charge concentration at a sharp point to
field evaporate atoms froma conical-shaped sample. The
collected atoms are then reconstructed into their original
positions using a computer algorithm making use of a
position-sensitive detector and time-of-flight measure-
ments. The nature of the data collection and the digital
reconstruction are what provide the unique 3-D capabili-
ties. Once accurately reconstructed, buried nanofeatures
can be isolated and examined from any and every angle.
Atomic profiles can be measured throughout layers or
across interfaces. Trace contaminant or dopant profiles
can be mapped. Various films or materials can be high-
lighted for clearer visualization. Various isotope ratios can
bemeasured. Theseexamples exhibit thepower of 3-DAPT
and demonstratewhy it is quickly growing in popularity in
a large number of fields. This article discusses the basics
of APT sample preparation, data collection, and analysis
by looking at a case study focused on state-of-the-art fin-
shaped field-effect transistors (FinFETs).
THE MAKING OF AN APT TIP
Typical APT sample preparation follows a similar pro-
cedure to that proposed by Thompson et al.,[12] where an
initial lamella is pulled in a similar fashion to transmission
electron microscopy (TEM) sample preparation. Sections
of the wedge-shaped lamella (Fig. 1a) are then cut and
welded to narrow posts, where each section is prepared
into a separate APT tip. A focused ion beam (FIB) is used
to create the conical tip in a series of concentric milling
steps, where the center of the milling pattern is blanked
to protect the final area of interest.[13] With each step, the
diameter of the blanket portion of the pattern is shrunk,
and the FIB voltage and/or current can be gradually
decreased to reduce damage to the area of interest. The
final shape of the sample is generally comparable to that
of a sharpened pencil, such as the tip shown in Fig. 1(b).
The finished tip has a topmost diameter of 20 to 100 nm
“ATOM PROBE TOMOGRAPHY IS OF
HIGH INTEREST DUE TO ITS CAPABILITY
TO PROVIDE BOTH STRUCTURAL AND
CHEMICAL ANALYSIS OF BURIED
FEATURES FROM ANY DESIRED
PERSPECTIVE WITH SUBNANOMETER
RESOLUTION.”