ConstantinVahlas-Chemical Vapor Deposition Iof Metallic Films-From Unary Systems to Complex...

1Constantin VahlasSOPRANO Meeting, Caen, 17 July 20091

Chemical Vapour Deposition of Metallic Films:from Unary Systems to Complex Intermetallics

Constantin Vahlas

Institut Carnot CIRIMAT

Toulouse

[email protected]

Constantin VahlasSOPRANO Meeting, Caen, 17 July 20092

CVD: one of the most important methods for preparingmetallic and ceramic thin films and coatings

Protection (corrosion, wear)

Optical properties

Electronic properties

Magnetic properties

Decoration

New hybrid- properties


CVD coated steel tools

Segmented forming tool for automobile door

Drawing ring


Outline

Definitions

Reactors

Precursors

Precursors delivery systems

Surface events

Conformal deposition

Selectivity

Infiltration of preforms

Deposition on powders

Competitive reactions

Towards MOCVD processed metallic alloy coatings: the Al-Cu-Fe system

Concluding remarks


Definitions


Chemical Vapor Deposition: The general frame

Chemical vapor deposition is a process where one

or more volatile precursors are transported via the

vapour phase to the reaction chamber, where they are

decomposed on a heated substrate to produce high-

purity, high-performance solid materials.

Precursor: person or thing that comes before sth.

(Oxford Advanced Dictionary, 1989)

Halide

Molecular compound (MOCVD)


+

Main gas flow region

AdsorptionSurface reaction Diffusion

Dsorption

NucleationGrowth

LigandMetallic centre

Transport

Diffusion

Gas phase reaction

+

Formation of

precursor vapors

Vaporization

Sublimation

Liquid injection

Diagnostics:

- Gas phase

- Surface

Reactor

Configuration

& design

- Growth rate

- -structure

- Composition

- Phases

- Adhesion

Post deposition

Thermal treatments

Properties

Modelling:

- Reactor

- Transport phenomena

- Deposition chemistry

- Surface electronic properties

Substrate

The MOCVD process: a sequence of elemental steps which have to be understood, controlled and optimized

Selection of

molecular

precursors

Vapor pressure

Stability

Shelf life

Dissociation scheme

Synthesis

Cost

Environment


Chemistry in Chemical Vapor Deposition

In every CVD process, there is some path involving physical phenomena AND a reaction that converts the vapors to a solid.

Part of the task of designing the reactor and process is always to force this reaction to happen only where and when it is desired (typically on the substrate), and not everywhere else.

Undesired reactions result in particles which can fall onto the substrates, coating of chamber walls, and clogging of exhaust openings.

The approaches to achieving this selectivity typically rely on five levers:

Precursors chemistry

Temperature

Time

Pressure

Surface specificity.

+


Dsorption

NucleationGrowth

TransportTransport

Diffusion

Gas phase reaction

+

Substrate


No universal processing technique available!

Minimum waste

Access to all metals

High throughputLower substrate T

Conformal coverageEase of development

CVDPVD

Advantages


Reactors


Reactors

Gas phase introduction

By products & pressuremanagement

Deposition chamber


Low pressure UV Hg lamp

Air cooling

LN2 trap

B

h

Process activation

Thermal

Plasma

Photoactivation

Laser

Jian Mi, PhD thesis, Georgia Tech, 2006 S. Vidal, PhD thesis, Toulouse Natl. Pol. Inst, 2001

(hfa)Cu(COD)272 nm


CVD Reactor types 1: Hot wall

Precursor

inlet

higher throughput

large heated

surface area

precursor depletion

Unreacted

precursor

& byproducts


CVD Reactor types 2: Cold wall

better control of uniformity

lower throughput

Precursor

inlet

Unreacted

precursor

& byproducts


Moving the wafers at constant speed through a heated reactor chamber

Install CVD processes at appropriate positions in steel or glass facilities.

Controlled by temperature, process gas flow rate, and belt speed.

High growth rates High equipment throughput Good uniformity Capability to process large-

diameter wafers

CVD reactor types 3: Atmospheric pressure, conveyor belt or continuous flow reactors

Particulate formation from gas-phase

nucleation

High gas consumption

Requests frequent reactor cleaning


CVD reactor types 4: Coating parts in FBCVD reactors

Treating agent: inert oxide (the filler: Al2O3, SiO2, ZrO2, TiO2) + powder of source metal (the donor of the element to be coated)

Fluidizing gas: Inert gas + activator (halides, alcali metal halides)

Donor + activator vapor precursors of the coating forming element (3HCl + Al AlCl3+ 1.5 H2)

Kinkel et al., Steel Res. 1995, 66, 318


High T (>1000K), diffusion of the substrate material

Substrate: Ni

Donor: FeAl

Activator: NH4Cl

Coating: NiAl

Voudouris & Angelopoulos, High Temp. Mater. Process. 1998, 2, 165


Different types of reactors, depending on: The type of activation (thermal, plasma, photon)

The geometry (vertical, horizontal)

The activated parts (hot, cold wall)

The best choice of a films deposition technique depends on targeted application

In the case CVD is foreseen as the best solution, the optimum choice of the reactor configuration still depends on the particular specifications


Temperature related growth rate:the three main regions of the Arrhenius plot

T-1 / K-1

127 C

29

30

31

32

33

34

0.0005 0.0010 0.0015 0.0020 0.0025

Ln(growth rate / m

oleculecm

-2s

-1)

227 C394 C727 C1727 CFlux limited kinetics

Surfacereactionratelimitedkinetics

Competingprocesses

Taylor et al., J. Am. Chem. Soc., 1999, 121, 5220

+


Dsorption

NucleationGrowth

TransportTransport

Diffusion

Gas phase reaction

+

Substrate

TiO2 from Ti(OiPr)4

Ea

Ea: the minimum energy necessary for a specific chemical reaction to occur


Precursors

+


+

Substrate

Selection of

molecular

precursors

Vapor pressure

Stability

Shelf life

Dissociation scheme

Synthesis

Cost

Environment


Chemical Vapor Deposition: CVD depends on the availability of a volatile chemical which can be converted by some reaction into the desired solid film. What makes the vapors (that is, volatility)

How these vapors can react in the gas phase or on the surfaces to be converted into the film?


Evolution: larger possibilities, smaller scales, highercomplexity

Traditionnal CVD: Halogenide precursors (WF6, TiCl4, SiH2Cl2)

T > 700 C, limited possibilities

Metal-organic CVD & Organometallic CVD: Molecular compounds

Tamb < T < 600 C, numerous

possibilities, high complexity

W

C

C C

C

C

C

O

O

O

O

O

O

H

Al

Me2EtN H

H

+


Dsorption

NucleationGrowth

Transport

Diffusion

Gas phase reaction

+

Substrate

+


Dsorption

NucleationGrowth

TransportTransport

Diffusion

Gas phase reaction

+

Substrate

Butterf

ly chem

istry


Co-deposition: Specific criteria

Compatibility of transport & deposition conditions (e.g. T)

No gas phase interaction

Compatible surface chemistry

+


Dsorption

NucleationGrowth

Transport

Diffusion

Gas phase reaction

+

Substrate

+


Dsorption

NucleationGrowth

TransportTransport

Diffusion

Gas phase reaction

+

Substrate

The difference between a molecular compound and a metalorganic precursor

Molecular precursors:Compatibility, Transport properties

CVD

Microstructure

Optimizationmaterial/process

Quantum chemistry,thermochemistry,chimique chemical

kinetics

Properties

Diagnostics

Qualification

General criteria

Liquid rather than gas or solid

Convenient volatility

Thermal stability

High purity or easily purified

Long shelf life

Easy & clean decomposition on the substrate

Non toxic

Environmentally compatible

Low cost

impossible

to meet all crite

ria

Mau

ry, J. Phys. IV, C5, 1995, 449

CMA NoE

, 200

5 -


Precursor architecture: a major issue

Molecular Structure and Bonding Controls: Precursor Volatility Deposition kinetics Growth rate Composition -structure

H

Al

Me2EtN H

H

H

Al

Me3N H

H

Solid

(AlH3-TMA)ads (AlH3)ads + (TMA)adsAlH3,ads Alads + 3Hads3Hads 1.5H3,ads 1.5H3,g

Liquid

(AlH3-DMEA)ads AlH3,ads + (DMEA)adsAlH3,ads Alads + 3Hads3Hads 1.5H3,ads 1.5H3,g

Dubois et al. Surf. Sci. 1990, 236, 77 Kim et al. Appl. Phys. Lett. 1990, 236, 77


Vahlas & Brissonneau, Annales Chimie, Sci. Mater., 2000, 25, 81

Various solutions for various constraints


MOCVD of Re: a processing route beyond the state of the art

Re: interesting material for high T applications in structural systems and energy

High Tf (3453K), low vapor pressure @Tf (0.1 Pa @ 3073K), mechanical properties x2 those of W and Mo up to 1473K, excellent corrosion & fretting resistance @ high T (2nd to Os)

Elevated cost

Heterogeneous catalysis, heat exchangers, space and missiles propulsion, hot gas valves Sherman, et al., JOM., 1991, 20

Bryskin and Danek, JOM., 1991, 24

Re coatings:

Powder metallurgy: too expensive, too long, no net shape

High T CVD: ReF6 + H2, ~800 C, handling of fluorides and effluents

ReCl5 + H2, ~1200 C, non compact -structure


Transport behavior of Re2(CO)10

Important weight loss @ 503K : complete sublimation

Endothermic peak @ 503K : either decomposition and/or vaporization

Two small endothermic peaks @ 374K and 465K. Either crystallographic transformation or monomerization (supplier: 443K)

DTA

TGA

F. Juarez-Lopez, PhD thesis,

Toulouse Natl. Pol. Inst, 2005


Time (min)

0 200 400 600 800 1000

P (Pa)

0

100

200

300

400

500

600

425K (152 C)

381K (108 C)

397K (124 C)

Intense increase of P with t

Stabilized P @ 108 C:no decomposition

Saturated vapor pressure of Re2(CO)10

Slight increase of P with t

1/T (K)

0,0024 0,0026 0,0028 0,0030 0,0032

log10P(Torr)

-2

-1

0

1

152 C

108 C

72 C

54 C 40 C

33 C

124 C

log10P (torr) = - 3116,7/T(K) + 7,9689

Juarez et al., Electrochem. Soc. PV 2003-08, 538


T=408 C

P=1 atm

50 nm50 nm

Original, low-T process for Re films

10 m

Lafont, et al., Scripta Mat., 2004, 51(7), 699


Molecular compounds provide a much wider spectrum of use than traditional halide compounds

A long list of criteria for the qualification of a compound as a precursor for a CVD process

Extremely difficult if not impossible to satisfy all criteria: compromise

No universal precursor for all processes involving deposition of a given metal: one precursor for each application?


Precursor delivery systems

+


+

Formation of

precursor vapors

Vaporization

Sublimation

Liquid injection

Substrate


N2 flow rate (sccm)

0 2000 4000 6000 8000 10000 12000

[Al(acac)

3] flow rate (g/h)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

5 g

10 g

20 g

50 g

100 g

150 g max

Bubblers

V

V

V

Carrier gas

H2 N2 Ar

Mass flow

controller

Bubbler - pure liquid

or solid precursor

Fpr = (FcgPT/Ptot)[1 exp(-Q/Fcg)]

110 m

m

40 mm

110 m

m

40 mm


Precursor Delivery Systems - Direct Liquid Injection

Precursor mass flow rate

Pumping rate

Precursor concentration

Vapor pressure

NikNikloclocnene

CobaltocCobaltocnene

TIBATIBA

ArAr

H2H2

evacuationevacuation

NikNikloclocnene

CobaltocCobaltocnene

TIBATIBA

ArAr

H2H2

evacuationevacuation

: Precision, reproducibility

: Use of solvents (process &

effluents management), incomplete

evaporation, limited solubility, use of

chlorinated ligands)Carrier gas

H2 N2 Ar

Mass flow

controller

Bubbler - precursor

& solvent

Pump Gasification

Carrier gas

H2 N2 Ar

Mass flow

controller

Bubbler - precursor

& solvent

Pump Gasificationwww.kemstream.com


Precursor Delivery Systems Sublimation in a fluidized bed

Vahlas et al., Chem. Vap. Dep., 2007, 13, 123

Rapid & efficient mixing (isothermal operation)

Continuous operation

Scale up

High mass & heat transfer rates

Under development

Dbit gaz vecteur (sccm)

0 2500 5000 7500 10000 12500

Dbit Prcurseur (g/h)

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

US Pat. 2008 268143(A1)


The objective: To generate the vapors and transport them to the deposition zone

Robust, reliable precursor feeding systems are necessary for the scaling up and the industrial implementation of a CVD process

Stable feeding rate vs deposition time

High feeding rate: In the diffusion limited regime

To avoid starving regime


Adsorption

Surface reaction Diffusion

NucleationGrowth

+

Substrate

Desorption

Definitions

Reactors

Precursors

Precursors delivery systems

Surface events

Conformal deposition

Selectivity

Infiltration of preforms

Deposition on powders

Competitive reactions

Towards MOCVD processed metallic alloy coatings: the Al-Cu-Fe system

Concluding remarks


Surface events 1: conformal deposition

Fully conformal 10 nm Cu seed-layer on TiN barrier in a 200 nm structure Constantin VahlasSOPRANO Meeting, Caen, 17 July 2009

38

Surface events 2: Selectivity

Preparing patterned metal films:

Blanket deposition + selective area etching

Blanket deposition into substrate trenches followed by chemical-mechanical polishing

Selective CVD

deposition of a material onto one surface (the growth surface) in the presence of another surface (the non-growth surface)

Cu on Si, not on SiO2

efficient

lessefficient


Mechanisms for selective deposition rely on:- inhibiting adsorption and reaction of the precursor and nucleation of the

metal on the non growth surface,- promoting these processes on the growth surface

1. Intrinsic reaction rate of the precursor on the non-growing surface slower than on the grow surface and on the growing film

2. The growth surface (e.g. Si) acts as a reducing agent and is selectively, sacrificially consumed by the precursor (e.g. WF6)

3. Dissociation of a co-reactant (a reducing agent, e.g. H2) occurs on the growth surface (e.g. a metal) but not on the adjacent non-growth surface (e.g. SiO2, polymer, metal oxide)

4. Rate increase on the growth surface by photo-chemically driven reactions

5. Selective passivation of the non-growth surface prevents adsorption of the precursor on the non-growth surface while adsorption and reaction occur on the growth surface

6. A species is present on the non-growth surface that getters (removes) the nucleating species

7. A free energy barrier for the formation of the metal nuclei inhibits nucleation on the non-growth surface; smaller barrier on the initial growth surface allowing for physical nucleation to occur


Surface events 3: infiltration of preforms; a case study

Potential technological applications & markets for a proprietary material developed by an SME :

Materials solutions for the air treatment in small volumes (passengerscabins in cars, space stations)

Catalytic converters made of metallic carriers

Catalytic support(e.g. -Al2O3) some 100 nm

Catalyst particles(e.g. Pt) some nm

some 10 msome 10 m


i. The substrate

SS, Cu, Ni = 19 mm e = 1 mm Porosity 50 and 70% Pores size 20 and 100 m BET = 0.5 2 m2/g SEF = 30 190 m2/m2


Al2O3 as a catalyst support

Levin & Brandon, J. Am. Ceram. Soc., 1995, 81(8), 1998-AlOOH -Al2O3

-Al2O3: convenient catalyst or catalytic supportLiu & Truitt, J. Am. Chem. Soc., 1998, 119, 9856

300 500 C

Impregnation of boehmite in vacuum

Calcination at 450C/4 h

Alphonse & Courty, Thermochim. Acta, 2005, 425, 75


Al2O3 covers the internal surface


Pt(acac)2 @(390 C, 50 Torr) Pt

Pt by F-MOCVI on Al2O3


Pt concentration higher at the entrance side of the disk and at its central part


200 nm200 nm200 nm

tdeposition = 60 min Pt = 4.5 wt % BET = 5 m2/g

High Pt load


100 nm100 nm100 nm

tdeposition = 10 min Pt = 0.3 wt % BET = 15 m2/g

Low Pt load


0

10

20

30

40

50

60

70

80

90

100

140 160 180 200 220 240 260

Temperature (oC)

CO conversion (%)

CO to CO2 conversion

O2/CO = 0.33

tcontact = 0,0053 s

T50 = 203C, 209C

- O2/CO = 0.5tcontact = 0.0400 sT50 = 199C

Cho et al., Cat. Lett., 2005, 103, 257

- O2/CO = 99/1tcontact = 0.0480 sT50 = 98C

Carberry et al, Cat. Lett., 1990, 4, 43

Similar catalytic activity for both loads

Christoglou et al., Surf. Coat. Tech., 2007, 201, 9195

Compares favorably with state of the art


Surface events 4: Deposition on powders

particle coatings for

nuclear applications

thick and continuous deposits on dense

(non-porous) powders

Large scale production of new classes of materials: supported catalysts,

nanomaterials

Vahlas et al. Mat. Sci. Eng. R 2006, 53, 1


CVD on powders: major differences from deposition on flat substrates

LARGE available surface:

surface reactions are so extended that gaseous precursors are very often totally consumed a few centimeters after their entrance into the fluidised-bed reactor in a laboratory scale contactor

compensated by vigorous mixing: uniform deposition

High heat transfer rates:

Isothermal conditions

Available growth surface per heated volume (m2/m3)

1e+1 1e+2 1e+3 1e+4 1e+5 1e+6 1e+7 1e+8

. FBCVD on porous particles

. CVI

. FBCVD on dense particles

. Hot wall multiwafer tubular

. Single wafer


Chemical engineering findings

The objective:

Each particle will present its entire surface to the gaseous reactants during the process

FB:

A bed of solid particles over a gas-distributing plate (often called the grid), is made to behave like a liquid by passing gas through it at a flow rate above a certain critical value


The Geldard diagram

Group A (20150 m, < 2 g/cm3) & B (sand): easy

Group D: large particles

Group C: cohesive

small size

strong electrostatic charges

wet, sticky non spherical materials

No sharp separation

Fluidization and powder classification:The basic principles

Crossing of the bed by the gas flow results in a pressure drop (P) through the bed ( essential information on the characteristics of the bed).


Improve the performance of gas turbines Increase combustion temperature

Increase components temperature

Risk of degradation

Superalloy

MCrAlY

Al2O

3-

YSZ

Hot Gas

Al2O3

Superalloy

MCrAlYMCrAlY

Al2O

3-

YSZYSZ

Hot Gas

Cooling Air

Therm

al Barrier

Superalloy

MCrAlYMCrAlY

Al2O

3-

YSZYSZ

Hot Gas

Al2O3

Superalloy

MCrAlYMCrAlY

Al2O

3-

YSZYSZ

Hot Gas

Cooling AirCooling Air

Therm

al Barrier

Application of a thermal barrier

Doping of the bond coats by different metals (Zr, Hf, Re, Ru) is beneficial to the mechanical and/or oxidation resistance of the barriers (e.g. Czech et al., Surf. Coat. Techn., 1995, 76-77, 28)


Praxair, NI-482 powders

50 m50 m

wt %Ni 42Co 23 Cr 20 Al 8Y 1Ta 5

High densitySpherical shapeAgglomeratesLarge size distribution Particles belonging to

groups C, A et B

NI-482 particles size (m)

10 100 1000

NI-4

82 particle

s

size distrib

ution (%

)

0

1

2

3

4

5

6

7

8

NI-482density

are off Geldarts classification

10


a

b

c

de

The MOCVD process requires fluidization in a spouted bed

0,00 0,01 0,02 0,03 0,04

0

200

400

600

800

1000

1200

1400

1600

1800

0,00 0,01 0,02 0,03 0,04

P (Pa)

0

200

400

600

800

1000

1200

1400

1600

1800

H/D=1,5

0,00 0,01 0,02 0,03 0,04

0

200

400

600

800

1000

1200

1400

1600

1800

Gas velocity (m/s)

0,00 0,01 0,02 0,03 0,04

P (Pa)

0

200

400

600

800

1000

1200

1400

1600

1800

H/D=1,5

0,00 0,01 0,02 0,03 0,04

0

200

400

600

800

1000

1200

1400

1600

1800

0,00 0,01 0,02 0,03 0,04

P (Pa)

0

200

400

600

800

1000

1200

1400

1600

1800

H/D=1,5

0,00 0,01 0,02 0,03 0,04

0

200

400

600

800

1000

1200

1400

1600

1800

Gas velocity (m/s)

0,00 0,01 0,02 0,03 0,04

P (Pa)

0

200

400

600

800

1000

1200

1400

1600

1800

H/D=1,5

which should be optimizedtaking into account the constraints of the powders

Caussat et al., Powder Techn., 2006, 165, 63


The design of the reactor considers the constraints both of the fluidization and of deposition

Filters

Grid (Powder beforespouting)

H2/ O2

N2Spouted bed

Frit Precursors: Ru(C5H5)2Re2(CO)10

SSteel reactor

Gas panel

Juarez et al., J. Phys. IV., 2001, 11, 1117


10 m

SEM EDS Ru

Deposition of Ru from RuCp2 + H2T = 898KQRuCP2 = 0,30 sccmQH2 = 428 sccmUgas > Ums

Vahlas et al., Chem. Vap. Dep., 2002, 4, 127


Theta (degrees)

10 20 30 40 50 60

Ru doped

NiCoCrAlY

Ru JCPDS 6-663

1 wt % Ru Well defined crystallites

50 nm50 nm50 nm50 nm

D1

D2

D3D4

D5

D1

D2

D3D4

D5

D (cm) dexp (nm) Plane dJCPDS #6-663

1 0,85 0,235 100 0,2343

2 1,0 0,211 002 0,2142

3 1,28 0,205 101 0,2056

4 1,68 0,157 102 0,1581

5 2,10 0,119 103 0,1219

C contamination: C/Ru=4

Lafont et al., Scripta Mat., 2004, 51(7), 699


10 mSEM QSB

EDS Ru

Homogeneous distribution of the deposit Ru 0,90 wt % No C contamination

Deposition from RuCp2 + O2T = 523KQRuCP2 = 0,36 sccmQO2 = 160 sccm


Continuous film, composed of ~30 nm crystallites

100 nm100 nm100 nm100 nm

50 nm50 nm50 nm50 nm

ConstantinVahlas-Chemical Vapor Deposition Iof Metallic Films-From Unary Systems to Complex...

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