chemical vapor deposition of manganese nitride
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• Doctoral research performed at the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign, in collaboration with chemistry students in Dr. Gregory S. Girolami’s research group
• Submitted to Chemistry of Materials for publication, published in doctoral thesis in October 2009
Amount of assumed background knowledge and information:
Assumed knowledge areas: Basic chemistry and physics knowledge, chemical nomenclature, ball and stick structures, lability due to spin states, the basics of chemical vapor deposition as a technique, familiarity with a variety of materials characterization techniques and ability to interpret the raw data from them
Chemical Vapor Deposition of Manganese Nitride
Teresa S. Spicer, PhD, PMPteresa.s.spicer@gmail.comhttp://www.linkedin.com/in/teresaspicer
Integrated circuits have created a vital industry and enabled the telecommunications revolution
Semiconductor industry plays an important role in globalization, and therefore also in shaping our collective future.
Global Semiconductors Market Value, $ billion, 2004-2013(e)
Source: Datamonitor
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Image from http://www.textually.org/
Miniaturization drives integrated circuit development and applications
Image from http://tunicca.wordpress.com/2009/07/21/moores-law-the-effect-on-productivity/
Materials and thin film processing are key to miniaturization
In order to continue miniaturization, thin films of new materials are required.
2007: 30 new materials introduced into 45-nm node1
1 A Thorough Examination of the Electronic Chemicals and Materials Markets, Businesswire, August 15, 2007 Image from http://www.intel.com/pressroom/kits/45nm/photos.htm
❝The implementation of high-k and metal materials marks the biggest change in transistor technology
since the introduction of polysilicon gate MOS transistors in the late
1960s.❞Gordon Moore, Intel Co-Founder, regarding two of the 30
new materials introduced in 2007
Manganese nitride CVD could be used in both electronic and spintronic devices
http://static.howstuffworks.com/gif/recover-data-hard-drive-2.jpg
Magnetic layers in microelectronics
• Mn4N is ferrimagnetic
• Mn3N2, MnN are antiferromagnetic
http://www.wmi.badw-muenchen.de/research/images/electron.jpg
Mn doping of GaN for spintronics
• Ga1-xMnxN is a magnetic semiconductor at RT
• Current Mn source: Manganocene, high T required
Synthetic inorganic chemistry and materials engineering are required for new CVD processes
Conception and synthesis of new CVD precursor candidates
CVD of films from precursor
Measurement of film properties
Process hypothesis development
Synthesis of modified precursor
Development of novel growth processes and chemistryare needed to develop good CVD processes.
Synthetic inorganic chemistry
Materials engineering
Tried-and-true concept:
N H
H
H+
Example: Tetrakis(dimethylamido)-titanium(IV) + NH3 → TiN films1-4
1 Dubois, L. H.; Zegarski, B. R.; Girolami, G. S. J. Electrochem. Soc. 1992, 3603–3609. 2 Dubois, L. H. Polyhedron 1994, 13, 1329–1336.
3 Prybyla, J. A.; Chiang, C. M.; Dubois, L. H. J. Electrochem. Soc. 1993, 2695–2702. 4 Fix, R. M.; Gordon, R. G.; Hoffman, D. M. Chem. Mat. 1990, 235–41.
Dialkylamide precursors in particular have worked very well in the past.
Many previous transition metal nitrides have been deposited from amides reacted with ammonia
M NN
RR
R R
Previously, few volatile precursors for Mn-N were known
Due to the size of Mn(II), sterically bulky ligands are required to prevent di- or polymerization of the precursor.
Zinc
30
Zn65.39
Nickel
28
Ni58.693
Cobolt
27
Co58.933
Iron
26
Fe55.845
Scandium
21
Sc44.956
Titanium
22
Ti47.867
Vanadium
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V50.942
Chromium
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Cr51.996
Manganese
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Mn54.938
Copper
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Cu63.546
Shannon-Prewitt Crystal Ionic Radii of Cations1
Most common oxidation state shown in bold.1
1 Wulfsberg, G. Principles of Descriptive Inorganic Chemistry. University Science Books, Sausalito, CA, 1991.
+388 pm
+2100 pm
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+472 pm
+568 pm
+294 pm
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+658 pm
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+760 pm
+292 pm
+378 pm
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+288 pm
+375 pm
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+291 pm
+387 pm
Bis[di(tert-butyl)amido]manganese(II) is a monomer and volatile
When reacted with ammonia, bis[di(tert-butyl)amido]Mn(II) should give manganese nitride films.
Spicer, C. W. Synthesis, Characterization and Chemical Vapor Deposition of Transition Metal Di(tert-butyl)amido Compounds. Doctoral dissertation, University of Illinois at Urbana-Champaign: Urbana, IL, 2008.
30% probability surfaces shown.
Films were deposited with and without ammonia
Experiment sets:
• Varying T, constant NH3 flow
• Varying NH3 flow, constant T
Substrates:
• Cr-coated Si(100)
Deposition in vacuum chamber➡ In-situ ellipsometer monitors growth➡ Precursor heated to 40 ºC➡ N2 carrier gas
Without NH3
Substrates:
• Si(100)
• α-C TEM grids
Experiment set:
• Varying T
With NH3
N H
H
H
Film phase, composition, roughness, and microstructure data were collected
Auger electron spectroscopy
X-ray diffraction
X-ray photoelectron spectroscopy
* Select films
With NH3 Without NH3
Deposition in vacuum chamber➡ In-situ ellipsometer monitors growth➡ Precursor heated to 40 ºC➡ N2 carrier gas
Transmission electron microscopy* Scanning electron microscopy
Atomic force microscopy
The growth rates are high considering the low growth temperatures
The reaction between bis[di(tert-butyl)]amidoMn(II) and ammonia is very facile.
Ammonia flow: 4.3 sccmPrecursor partial pressure: 0.2 - 0.4 mTorrTotal chamber pressure: 1.6 mTorr
In the absence of ammonia, severely carbon-contaminated films of Mn are obtained
Ammonia is key to growing films of manganese nitride.
Auger electron spectrum of Mn film grown at 300 ºC
41.5 at. % C38.4 at. % O20.0 at. % Mn
The reaction is likely a transamination
The analogous results in other respects suggest that the reaction mechanism is also analogous.
First step of tetrakis(dimethylamido)Ti(IV) transamination
Analogous first step of bis[di(tert-butyl)amidoMn(II) transamination
+ NH3Ti
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Films can be deposited at temperatures as low as 80ºC in the presence of ammonia
The reaction between bis[di(tert-butyl)]amidoMn(II) and ammonia is very facile.
500 nm
With NH3
N H
H
H
Without NH3
• No growth until 400 ºC
• Even at 400 ºC, growth rate is only 0.4 nm/min
• Growth rate is 2.1 nm/min
The film phase and composition depend on growth temperature
The film grown at 300 ºC is markedly different from those grown at 200 ºC and below.
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N
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Inte
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rbit
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its
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2-theta
η-Mn3N2
Mn2N1.08
Mn23C6
(103) (110)
(006) (200)
(202) (213)
(0 0 10)
(206)
(420)
(101)
(102) (110)
(611)
(440)
(422)
(531)
XRD diffractogramsAES-derived elemental
compositions
80-100 ºC: Crystalline grains of η-Mn3N2 embedded in an amorphous matrix
The extremely low growth temperature inhibits complete crystallization of the films at 80 and 100 ºC.
XRD diffractogram Brightfield TEM image
Insets: convergent-beam diffraction patterns from nm-
sized areas indicated in image
200ºC: Fully crystalline films of η-Mn3N2
The high-quality crystallinity at merely 200 ºC is unusual.
TEM images and patternsLeft: Convergent-beam diffraction patterns from six different nm-sized areas
Below: Brightfield image with diffraction pattern inset
XRD diffractogram
300 ºC: 40% Mn3N2, 40% Mn2N1.08, 20% Mn23C6
At 300 ºC, the ammonia supply may have been insufficient to deposit a single phase.
1 µm
AES elemental composition
• 67% Mn
• 16% N
• 17% C0
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Inte
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ou
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2-theta
η-Mn3N2
Mn2N1.08
Mn23C6
(103)
(110)(006)
(200)(202)
(213)
(0 0 10)
(206)
(420)
(101)
(102)
(110)
(611)
(440)
(422)
(531)
XRD diffractogram
The crystallinity and high growth rates can be attributed to high-spin Mn(II)
Surface species are likely to remain reactive and mobile and can settle into low-energy ordered arrangements.
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Deposition temperature (ºC)
Low-temperature crystallinityConvergent-beam diffraction patterns from
six different nm-sized areas, all showing diffraction through crystalline η-Mn3N2
High growth rates for low temperaturesAny growth at 80ºC is surprising, especially at
rates of several nanometers a minute
CVD of Manganese Nitride
• Very facile, due to the lability of high-spin Mn(II)
• Transamination of precursor with ammonia
• Films of η-Mn3N2 films can be grown at 80ºC
Acknowledgements
Dr. Charles Spicer, UNCCDr. Bong-Sub Lee, UIUC
Kristof Darmawikarta, UIUCDr. Angel Yanguas-Gil, UIUC
Dr. Mauro Sardela, UIUCNancy Finnegan, UIUC (Ret.)
Dr. Tim Spila, UIUCDr. Richard Haasch, UIUC
Subhash Gujrathi, Université de Montreal
Research supported by NSF grant DMR-0420768
Film characterization was carried out in the Center for Microanalysis of Materials, University of Illinois, which is partially supported by the U.S. Department of
Energy under grant DEFG02-91-ER45439
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