• 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

Outline

Introduction

Key Findings

Problem Statement

Experiments

Results

Introduction

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

Problem Statement

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

23

V50.942

Chromium

24

Cr51.996

Manganese

25

Mn54.938

Copper

29

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

+381 pm

+474 pm

+283 pm

+374 pm

+288 pm

+293 pm

+378 pm

+472 pm

+568 pm

+294 pm

+375 pm

+469 pm

+658 pm

+297 pm

+378 pm

+467 pm

+760 pm

+292 pm

+378 pm

+472 pm

+288 pm

+375 pm

+467 pm

+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.

Experiments

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

Results

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

Me

N

Me

Me

Me

N

Me

N

Me

MeN

Me

H

H

NTi

Me

N

Me

Me

N

Me

MeN

Me

+

Me

Me

NH

+ NH3 +Mn

t-Bu

N

t-Bu

t-Bu

t-Bu

N

H

H

Mn N

t-Bu

N

t-Bu

H

t-Bu

t-Bu

N

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.

Mn

N

C

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Inte

ns

ity

(A

rbit

raty

un

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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2-theta

η-Mn3N2

Mn2N1.08

Mn23C6

(103)

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(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

Key Findings

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