2011 ITRS Metrology Roadmap

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2011 ITRS Metrology Roadmap

Alain Diebold

Empire Innovation Professor of Nanoscale Science

College of Nanoscale Science and Engineering

257 Fuller Road

Albany, NY 12203


The continued interest in metrology was evident during 2011. Technical challenges were again
accelerated as 3D device structures such as the FinFET
and Through Silicon Vias (TSVs)
went from the
research stage to

manufacturing.
The
interest was also evi
dent as the
Metrology Technical Working
Group
(TWG)
increased participation and replaced key representatives.
As with previous years, the
Metrology Roadmap is a collaborative effort between the Metrology TWG and the other TWGs. Process
requirements are
drawn from
Emerging
Research
Materials
, Emerging Research Devices,
Lithography,
FEP, Interconnect, Process Integration, Devices and Structures, and Assembly and Packaging. As a cross
-
cutting TWG, Metrology also relies on the information from Modeling and
Simulation, Yield
Enhancement, and Factory Integration.

In this article, the main challenges for 2011 are highlighted, and
a few new measurement needs emphasized.


Emerging Research Materials Metrology

Over the past several years, graphene devices have be
en the most visible example of the strong
international interest in the Nanoelectronic
s

Research Initiative’s

(NRI)

search for a new switch to
replace the transistor
. During 2011, efforts to fabricate large area graphene included the now well
-
known thermal

processing of SiC and Chemical Vapor Deposition of graphene on metals substrates
,

especially copper.
(1)

The grain size and grain boundary structure of CVD graphene is significant because
the grain boundary structure is believed to have a significant impact on
the electron transmission
prop
erties.(
2
) Recent aberration corrected scanning transmission electr
on microscopy images of grain
boundaries and edge structures point to the challenges in imaging grain boundaries and the significant
influence of local structure on electronic properties.(
3
,
4
)

Armed with this information, other groups are
characterizing
the structure and optical properties of CVD graphene.(5)

An example of the
characterization of CVD graphene is shown in figure 1.
In
-
Line cleanroom measurements of graphene on
SiO2 and other surfaces have already been demonstrated.(6)



Although graphen
e device research is clearly an important area, the ERM Roadmap describes a number
of metrology needs for other materials and devices.


One example is Redox memory devices
,

such as
memristors. A concerted effort is required to understand the physical mec
hanisms involved in device
operation. Operation of the devices involves formation of conducting nanofilaments in the TiO
2

between metal electrodes.
Recently, transmission electron microscopy(7
, 8
), synchrotron based
scanning transmission
X
-
Ray microscopy

(STXM)

(9)

with chemical analysis using
near edge
X
-
Ray
absorption fine structure

(NEXAFS)
(
10
),
and photoemission electron microscope (PEEM)(
10
)

have
observed the formation of a stable

Magneli Ti4O7 phase


in the TiO
2
.

This characterization is
challengi
ng and far from routine.
Filament characterization also illustrates the difficulties involved in
understanding new materials.


FEP Metrology

Alternate channel materials and
3D device structures are key areas of interest for FEP metrology.
Germanium and
III
-
V channel materials are expected to require characterization m
ethods capable of
accessing crystalline defects in patterned structures. Although blanket film characterization of the
film
stacks is difficult, characterizing film stress and defectivity i
n sub 20 nm gate length transistors is even
more challenging.



Compl
e
mentary

Metrology


The use of multiple method
s

to improve capability
:
FEP & Lithography
Metrology for FinFET transistors



an example

The topic of Compl
e
mentary

Metrology has been
of considerable interest during 2011 as evidenced by
the
Metrology, Inspection, and Process Control for Microlithography XXV conference
,

which is part of
the
SPIE Advanced Lithography conference.


Alok Vaid’s invited talk used the term “Hybrid Metr
ology”
and discussed a holistic approach to improving CD measurement. (11) This approach takes the long used
concept of using multiple methods to verify a measurement value and combines it with advanced
software. Similar concepts have motivated Advanced E
quipment and Advanced Process Control.


The 2011 Metrology TWG discussions have illustrated the wide ra
nging applicability of Compl
e
mentary
Metrology, and the TWG uses FinFETs as a key example.
As shown in Figure 2, FinFET

transistor
processing requires measurement of a number of different dimensions and other properties on a 3D
structure that starts with a single crystal “fin” of si
licon. Various layers such as h
afnium dioxide based
high


and a metal gate electrode stack

have dimension
s

that cover the sides and top of the fin. The
doping m
etrology is also challenging, and
scanning spreading resistance microscopy has proven itself
invaluable in characterizing FinFETs.

(12)



Lithography Metrology

The need for production
worthy EUV patterning is driving research and development of metrology for
mask substrates, mask blanks, and patterned masks. Two distinctly different types of defects must be
detected: phase defects and amplitude defects. These are illustrated in Figure

3.


3D Interconnect Metrology

The 2011 Metrology Roadmap contains an expanded description of the metrology needs for through
silicon vias (TSV). Although TSVs are only one kind of 3D interconnection, their measurement needs
have received wide
spread atte
ntion.
Last year’s Future Fab article on the Metrology Roadmap illustrates
recent advances in TSV metrology.(13)


Acknowledgements

The following have participated in the 2011 ITRS Metrology TWG:

Carlos Beitia (
CEA LETI MINATEC
),
Ben Bunday (SEMATECH)
, Alai
n
Diebold (CNSE), Brendan Foran
(Aerospace), Christina Hacker (NIST), Karey Holland (FEI), Masahiko Ikeno (Hitachi High
-
Tech)
,
Eiichi
Kawamura (Fujitsu Semiconductor),

Adrian Kiermasz (Metryx), Delphine Le Cunff (ST), Scott List (INTEL),
Philippe Maillot (
ST),

Yaw Obeng (NIST
)
, George Orji (NIST),

Dave Seiler (NIST)
,
Chin Soobok (Samsung),
Vic Vartanian (SEMATECH)
,
Andras Vladar (NIST),
Yuichiro Yamazaki (Toshiba)





References:

1.

J. An, E. Voelkl, J. Suk, X. Li, C. W. Magnuson, L. Fu, P. Tiemeijer
, M. Bischoff, B. Freitag, E.
Popova, R. S. Ruoff. Domain (Grain) Boundaries and Evidence of "Twin
-
Like" Structures in CVD
Grown Graphene. ACS Nano
5
(4) 2433, 2011.

2.

O.V. Yazyev and S.G. Louie, Electronic transport in polycrystalline graphene, Nature Mate
rials,
9
,(2010), pp
806

809
.

3.

P.Y. Huang, C.S. Ruiz
-
Vargas, A.M. van der Zande, W.S. Whitney, M.P. Levendorf, J.W. Kevek, S.
Garg, J.S. Alden, C.J. Hustedt, Y. Zhu, J. Park, P.L. McEuen
, D.A. Muller, Grains and Grain
Boundaries in Single
-
Layer Graphene Atomic Patchwork Quilts, Nature 469, (2011), pp 389
-
392.

4.

K.Suenaga & M. Koshino, Atom
-
by
-
atom spectroscopy at graphene edge, Nature 468, December
2010, 1088.

5.

F. Nelson, V. K. Kamineni, T. Zhang, E. S. Comfort, J. Lee and A. C. Diebold,
App. Phys. Lett.,
97
, 253110 (2010).


6.

F. J. Nelson, V. K. Kamineni, T. Zhang, E. S. Comfort, J. Lee, A. C. Diebold
,
Spectroscopic
Ellipsometry of CVD Graphene,

7.

D
-
H Kwon, K. M.
Kim, J. H. Jang, J. M. Jeon, M. H. Lee, G. H. Kim, X.
-
S. Li, G.S. Park, B. Lee, S.
Han, M. Kim, and C. S. Hwang,
Atomic structure of conducting nano
-
filaments in TiO2 resistive
switching memory, N
ature Nanotechnology

(2009).

8.

W. M. Tong, J. J. Yang, P. J.
Kuekes, D. R. Stewart, R. S. Williams
,
E. DeIonno, E. E. King, S. C.
Witczak, M. D. Looper, and J. V. Osborn
,

Radiation Hardness of Memristive Junctions, IEEE
Trans. on Nucl. Sci.
57
, (2010), 1640.

9.

J. P. Strachan, D.B Strukov, J. Borghetti, J.J. Yang, G.
Medeiros
-
Ribeiro

and R S.Williams
,
The
switching location of a bipolar memristor: chemical, thermal and structural mapping,
Nanotechnology
22
(2011) 254015.

10.

J. P. Strachan, J.J. Yang, R. Munstermann, A. Scholl, G. Medeiros
-
Ribeiro
, D.R. Stewart,
and R.
S.

Williams
,
Structural and chemical characterization of TiO2 memristive devices by spatially
-
resolved NEXAFS,
Nanotechnology
20
(2009) 485701.

11.

A. Vaid, et al,
A holistic metrology approach: hybrid metrology utilizing scatterometry, CD
-
AFM,
and CD
-
SEM,
Proceedings Vol. 7971
,
Metrology, Inspection, and Process Control for
Microlithography XXV,
C.
J. Raymond
,
Editor, (2011), p

797103
.

12.

J. Mody, P. Eyben, E. Augendre, O.


Richard, W.


Vandervorst,
Toward extending the capabilities
of scanning spreading resistance microscopy for fin field
-
effect
-
transistor
-
based structures,
J.
Vac. Sci. Technol. B
26
, (2008), p
351.


13.

http://www.future
-
fab.com/documents.asp?grID=392&d_ID=4797



Figures:





Figure 1.

Dark Field Transmission Electron Microscopy image of grains in CVD graphene.

Grains having the same color have the same crystallographic orientation. Figure courtesy
Florence Nelson, College of Nanoscale Science and Engineering.






















Figure 2.
Complex structures such as FinFETs require 3D metrology
. 12
parameters in diagram
require dimensional measurement

not counting top corner rounding, footing, or etch recess
under fin.

Exaggerated sidewall angle angles are used in this figure.










Figure 3.

EUV Phase and Amplitude defect types are illustrated. Figure courtesy Phil Seidel,
SEMATECH

from 2004.