ALD an Enabler for Nanoscience and Nanotechnology Gordon Harvard Revied Amide Compounds

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Harvard University

Atomic Layer Deposition (ALD): An Enabler

for Nanoscience and Nanotechnology

Roy G. Gordon

Harvard University

Cambridge, MA



Harvard University

Definitions of Chemical Vapor Deposition (CVD)and Atomic Layer Deposition (ALD)

Structures and materials made by ALD

Properties needed for CVD and ALD precursors:

Volatility, Stability, Reactivity

How to design those properties into precursors:

metal amidinates

High-k insulators: La2O3, LaAlO3

Outline



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Chemical Vapor Deposition (CVD)

One or more gases or vapors react to form a solid product

Reaction started byheat

mixing 2 vapors

plasma

Solid product can be afilm

particle

nanowire

nanotube

precursor vapors

byproductvapors

substrate

film

Heater



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Benefits of ALD:

• Atomic level of control over film composition⇒nanolaminates and multi-component materials

• Uniform thickness over large areas and inside narrow holes

• Very smooth surfaces (for amorphous films)• High density and few defects or pinholes

• Low deposition temperatures (for very reactive precursors)

• Pure films (for suitably reactive precursors)

Sequential, self-limiting surface reactions make alternating layers:

Atomic Layer Deposition (ALD)

Heated area =

deposition zone

Precursor 1

Precursor 2



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Typical ALD Reaction for Oxides

OH OH OH

ML2

ML2

ML2

ML

O

ML

O

ML

O

HL HLHL

ML

OML

O

ML

O

H2O

H2OH2O

MOH

OMOH

O

MOH

O

HLHL

HL



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metal amidinates


Outline



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Lining and Fill ing Holes by ALD

4 cycles 12 cycles



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Nanopores by ALD

Ion Mill ing

Ion Milling + ALD

May be used for rapid sequencing of DNA



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Coatings on the Outside of Particles

ALD AlN coating

ZnS particles

Used in electroluminescent back-lights for displays

in cell-phones and many other devices.



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Photonic Crystals by ALD

f

500nm

1) Form crystals of silica spheres.

2) ALD of Ta2O5 between the spheres

3) Convert to Ta3N5 in NH3

4) Dissolve the silica spheres in HF

The resulting photonic crystals may be able to control light,

the way semiconductors control electron transport.



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Nano-Dots by ALD

ALD ruthenium

on aluminum oxide

nucleation density is

~ 20 x higher than previous

metal nanocrystals

40 nm scale bar; 10 nm in insertmay be applied to

flash memories

diameters ~1 to 2 nm,

~ 5 to 10 atoms across



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Nanobeads by ALD

after 500 cycles of Al2O3 after 500 cycles of iron

Growth on Single-walled Carbon Nanotubes



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Alumina Nanotubes on Carbon Nanotubes

100 nm diameter 21 nm diameter 7 nm diameter



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Nano-Coaxial Cable or Transistor

Conducting tungsten nitride (WN) concentrically around

insulating aluminum oxide (Al2O3) concentrically around

a conducting carbon nanotube.

Carbon Al2O3 WN Al2O3WN



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Elements included in ALD Materials

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Fr Ra Ac

Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Green = Element included in at least 1 ALD Material

Red = Element not included in any ALD Material



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Oxides Made by ALD

H HeLi Be B C N O F Ne


K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra Ac



Green = ALD process known for an Oxide of the Element

Red = no process known for ALD of any Oxide of the Element



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Pure Elements Made by ALD

H He

Li Be B C N O F Ne




Fr Ra Ac



Green = ALD processes known for 16 Pure Elements

Red = no process known for ALD of the Element



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Nitrides Made by ALD

H He

Li Be B C N O F Ne




Fr Ra Ac



Green = ALD processes known for a Nitride of the Element

Red = no process known for ALD of a Nitride of the Element



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Sulfides Made by ALD

H He

Li Be B C N O F Ne




Fr Ra Ac



Green = ALD processes known for a Sulfide of the Element

Red = no process known for ALD of a Sulf ide of the Element



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Carbides Made by ALD

H He

Li Be B C N O F Ne




Fr Ra Ac



Green = ALD processes known for a Carbide of the Element

Red = no process known for ALD of a Carbide of the Element



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Fluorides Made by ALD

H He

Li Be B C N O F Ne




Fr Ra Ac



Green = ALD processes known for a Fluoride of the Element

Red = no process known for ALD of a Fluoride of the Element



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Current Applications of ALDElectroluminescent displays (Al2O3, AlN, ZnS)Read/Write heads in magnetic disk storage (Al2O3)Insulators in capacitors in DRAMs (Al2O3, HfO2)

Insulation and spacer layers in microelectronics (SiO2, Si3N4)Metal/insulator in transistor gates (TaN/HfO2)Planar waveguides and optical filters (SiO2, TiO2)

Likely Future Applications of ALDInsulators in microelectronic capacitors (Ta2O5, SrTiO3, LaLuO3)Diffusion barriers for copper in interconnects (WN, TaN, Mn) Adhesion and seed layers for interconnects (Co4N, Ru, Cu)Sealing pores in low-k dielectrics (SiO2)Magnetic disk storage (Al2O3, Fe, Co, Ni, Cu, Ru, Mn, Pt)Nano-Electronics

Catalysts . . .

Applications of ALD



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metal amidinates


Outline



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Criteria for Both CVD & ALD Precursors

•Sufficient volatility (> 0.1 Torr at T < 200 oC)

•No thermal decomposition during vaporization

•Liquid at vaporization temperature

•Preferably liquid at room temperature

or soluble in an inert solvent

•Precursors and byproducts don’t etch fi lms





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Some precursors work only in CVD, but not ALD:

Ni(CO)4, W(CO)6, many alkoxides

Some precursors work in both CVD and ALD:

many beta-diketonates and amidinates

Usefulness of Precursors for CVD & ALD

CVD

ALDMost ALD precursors

also work in CVD

Some CVD precursors

also work in ALD



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metal amidinates


Outline



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Metal(II) Amidinates

R1

and R3

= alkyl groups Acetamidinates: R2 = CH3

N

M

N

R1

R2

R3

N

N

R2

R1

R3

monomer dimer

N

M

N

R2

N N

M

R3

R1

R3

R1

N N

R1R3

N

N

R1

R3

R2

R2

R2

Formamidinates: R2

= H

The choices of Rn affect the volatility, reactivity and stabil ity.

M-N bonds are generally reactive to H2O, NH3, H2, etc.

The chelate structure adds to the thermal stabili ty.

Propionamidinates: R2 = CH2CH3



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1351181001038378727473736569ionic radius

ddmtert-pentyl2

Bi

m

Zn

m

Ge

m

dn-propyl2

BaSr CaMnFeMgCr CoNiR1, R3

ppdddmEt-tert-Bu

ppddddmmmisopropyl2

dddmmmccctert-butyl2

Increasing “ size” of metal atom

I n

c r e a s i n g

l i g

a n d

b u l k

d = reactive, volatile dimer

Structures of Metal Bis-Acetamidinates

p = non-volatile polymer

m = more reactive, less stable, volatile monomer

c = crowded, less reactive, more stable, volatile monomer



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Metal(III) Amidinates

R1 and R3 = alkyl groups

Formamidinates: R2 = H

Acetamidinates: R2 = CH3

M

N N

N N

NN

C C

CR

3R

1

R3

R1

R1

R3

R2

R2

R2

monomer

Structures of dimers are unknown, probably bridged

Propionamidinates: R2 = CH2CH3



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ddmMe2

pmmmmmEt2

La

p

d

m

c

Ce

c

Pr

m

Nd

c

Eu

c

Gd

m

Y

d

m

c

V

c

Co

c

mmmmcn-Pr 2

LuSbScRuTiFeCr Ga AlR1,R3

mEt-

tBu

cccccccciso-

Pr 2

cnntert-

Bu2

Increasing size of metal atom

I n c r e a s i n g

l i g a n

d

b u l k

m = more reactive monomer

d = low-volatili ty dimer

Structures of Metal(III) Tris-Amidinates

p = non-volatile polymer

c = crowded, less reactive monomer n = non-existent



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Models for Lanthanum and Scandium Amidinates

La precursor reacts

quickly with surface OH

Sc precursor reacts

slowly with surface OH

La ion is large, so 3 amidinateligands are not crowded

Sc ion is small, so 3 amidinateligands are crowded

La

Sc



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Zr(amd)4 and Hf(amd)4

Metal(IV) Tetra-Amidinates

Require small Rn groups

such as H and CH3

CH3

N

N CH3

H

H3C N

N

CH3

H

CH3N

N

CH3

H

CH3

N

NH3C

H

Hf

Zr amidinate is much more stable

than Zr amide, Zr(NEtMe)4

Thermal decomposition at 200o

C

Greater stabili ty of amidinates is

due to chelate structure (2 metal-

nitrogen bonds instead of one)

O tli



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How to design those properties into precursors:metal amidinates

High-k insulators: La2O

3, LaAlO

3

Outline

Th i t i A l i f



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Thermogravimetric Analysis of

Lanthanum Amidinates

N

H

C N

N

CHNN

HC

N La

NC

N

N

CNN

C

N La

CH3

CH3H3C

NC

N

N

CNN

C

N La

CH3

CH3H3C

H3C CH3

CH3

CH3CH3

H3C

=> Vaporization temperature increases with molecular mass

V P f L th P



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Vapor Pressures of Lanthanum Precursors

=> La(iPr 2-fmd)3 is most

volatile La compound known,

60 mTorr at 100 oC

La(iPrCp)3

NHC

N

N

CHNN

HC

N La

0.1

Torr

ALD f L O



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ALD of La2O3

=> 0.16 nm per cycle

=> negligible delay

in nucleation on SiH

N

HC N

N

CHNN

HC

N La

tris(N,N’-diisopropyl-formamidinato)lanthanum

(iPr 2-fmd)3La

Precursors:H2O and

Growth per La Cycle for ALD LaAlO



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Growth per La Cycle for ALD LaAlO3

Bubbler temperature 90 to 120 oC

Substrate temperature 300 oC

Growth even at bubbler

temperature <100 oC

=> ALD saturation at0.08 nm per La cycle

N

HC N

N

CHNN

HC

N La


(iPr 2-fmd)3La

Precursors:Me3 Al, H2O and

120 oC110 oC

100 oC

90 oC

Composition of ALD La Al O



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Composition of ALD Lax Al1-xO3/2

Growth conditions:

Bubbler temperature 120 oC

Substrate temperature 300 oC

=> Composition control

by changing ratio of

precursor doses

=> 2 x as many Al atoms

as La atoms per dose

N

HC N

N

CHNN

HC

N La


(iPr 2-fmd)3La

Precursors:Me3 Al, H2O and

Precursor Reactivity with SiH Surface by IR



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Precursor Reactivity with SiH Surface by IR

=> Completely uniform surface coverage by La amidinate

Hf alkylamide only

reacts with half of

the Si-H bonds onthe surface even

after many cycles

La amidinate reactswith nearly all the

Si-H bonds in only

3 cycles

Details of the infrared data were given at AVS Conference ALD 2007 by

J. Kwon, M. Dai, E. Langereis, Y. Chabal, K.-H. Kim and R. G. Gordon.

TEMs of ALD LaAlO and GdScO



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TEMs of ALD LaAlO3 and GdScO3

=> Sharp interfaces with silicon without interlayers

=> Uniform nucleation and thickness

LaAlO3

Si2 nm

Leakage Current through ALD La O



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Leakage Current through ALD La2O3

Vapor source: a solution of the La precursor (mp 194o

C)vaporized with an MKS MDD liquid delivery system

Low leakage current similar to films made from a bubbler.

=> negligible carbon contamination from solvent

C i f l k



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Comparison of leakage

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.010

-8

10-6

10-4

10-2

100

102

SiO2

ALD LaAlO3

ALD GdScO3

ALD LaScO3

ALD HfO2 from IMEC (Ref.1)

MOCVD HfO2 from IMEC (Ref.2)

ALD HfO2 from IBM (Ref.3)

Sputter HfO2 (Ref.4)

L e a k a g e (

A / c m

2 )

EOT (nm, |Vg-V

fb|=1V)

Summary



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Summary

ALD requires volatile precursors with self-limited reactivityand high thermal stabili ty

Precursors with these properties are known for mostelements

ALD is a proven process with many current applications

Many more uses for ALD are expected in the future

Acknowledgements



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AcknowledgementsMetals: Booyong Lim, Antti Rahtu, Jin-Seong Park, Venkateswara Pallem

Cu, Co: Zhengwen Li, Séan Barry, Don Keun Lee, Harish Bhandari, Hoon Kim

Ruthenium: Huazhi Li, Titta Aaltonen, Jun Ni

Metal Nitrides: Jill Becker, Seigi Suh, Esther Kim,

Kyoung

young

-ha

a Kim

Metal oxides: Dennis Hausmann, Philippe de Rouffignac, Jin-Seong Park,

Kyoung

young

-ha

a Kim, Leo Rodriguez, Mike Coulter, Jean Sébastien Lehn, Sheng

Xu, Hongtao Wang, Yiqun Liu

TEM: Damon Farmer; Hongtao Wang, SEMATECH, Applied Materials

DRAM trenches supplied by Infineon Qimonda)

La, Co, Cu and Ru precursors supplied by Rohm and Haas Electronic Materials

SiO

2

and W precursors supplied by Sigma-Aldrich Company

SEMs and Electrical Analysis by Daniel Josell, NIST

Supported by the US National Science Foundation and Intel Corporation

Documents

ALD an Enabler for Nanoscience and Nanotechnology Gordon Harvard Revied Amide Compounds