in situ spectroscopic ellipsometry as a versatile tool to ... · 2 / department of applied physics...

1

In situ spectroscopic ellipsometry as a versatile tool to study atomic layer deposition

Erik Langereis

Department of Applied [email protected]://www.phys.tue.nl/pmp

Ellipsometry WorkshopEnschede, 11th February 2010

/ Department of Applied Physics – Erik Langereis

1 / 38Outline

• Atomic layer deposition (ALD)- Basics of ALD- Materials deposited by ALD- Applications for ALD

• In situ spectroscopic ellipsometry as tool to monitor ALD

Monitoring the film thickness- ALD growth & growth per cycle- Self-limiting chemistry - Initial film growth & substrate dependence- Nanolaminates

Parametrizing the dielectric function- Metallic films:

Electrical properties & electron scattering- Ultrahigh-k dielectrics

Film composition & microstructure

Thin film materials:

Al2O3

Ta2O5

Er2O3

TiO2

TiNTaN Ta3N5

SrTiO3

PtRu

2


2 / 38

Precursor APrecursor APrecursor APrecursor A

Basics of ALD

Atomic layer deposition (ALD) is a low temperature vapor-based deposition technique for ultrathin and conformal film growth with sub-monolayer growth control

use saturative surface reactions to ensure self-limiting film growth

Precursor BPrecursor BPrecursor BPrecursor B

Large variety in ALD materials by finding the appropriate combination of precursors


3 / 38

0 25 50 75 100 125 1500

3

6

9

12

15

Al 2O

3 film

thic

knes

s

Number of ALD cycles

Illustrative example: ALD of Al2O3

Al(CH3)3

H2O

ALD cycle

Submonolayer growth control

Film thickness is ruled bythe number of cycles chosen: Al2O3 ~1 Å growth per cycle

Heil et al., J. Appl. Phys. 103, 103302 (2008)

3


4 / 38

0 25 50 75 10010-11

10-10

10-9

10-8

H2O

Mas

s sp

ectr

omet

ry s

igna

l (A

)

Time (s)

CH4

Al(CH3) 3

Al(CH3) 3

Al(CH3) 3

Al(CH3) 3

H2O

H2O

H2O

H2O

0 25 50 75 10010-11

10-10

10-9

10-8

H2O

Mas

s sp

ectr

omet

ry s

igna

l (A

)

Time (s)

CH4

0 25 50 75 10010-11

10-10

10-9

10-8

H2O

Mas

s sp

ectr

omet

ry s

igna

l (A

)

Time (s)

CH4

Al(CH3) 3

Al(CH3) 3

Al(CH3) 3

Al(CH3) 3

H2O

H2O

H2O

H2O


Al(CH3)3

H2O

ALD cycle

Surface chemistry rules ALD process

Ligand exchange between Al(CH3)3 and–OH surface groups and H2O and –CH3

surface groups leads to CH4 formation

Heil et al., J. Appl. Phys. 103, 103302 (2008)


5 / 38Illustrative example: ALD of Al2O3

Al(CH3)3

H2O

ALD cycle

Surface chemistry rules ALD process

Surface alternately covered by –OH groups and –CH3 groups

4000 3500 3000 2500 2000 1500 1000

4x10-5

Infr

ared

abs

orba

nce

Wavenumber (cm-1)

OH

stretching

CHx

stretching

CHx

deformation

2940 cm-1 1207 cm-1

Al(CH3)3chemisorption

H2O

exposure

Langereis et al., Appl. Phys. Lett.. 92, 231904 (2008)

4


6 / 38

0 20 40 60 80 1000.0

0.4

0.8

1.2

Al(CH3)3 precursor

H2O oxidant

Gro

wth

per

cyc

le (

Å)

Precursor dose (ms)


Al(CH3)3

H2O

ALD cycle

Saturative surface reactions

Al(CH3)3 and H2O lead to self-limiting surface reactions that

become independent of precursor flux

van Hemmen et al., J. Electrochem. Soc. 154, G165 (2007)


7 / 38

0 2 4 6 80.0

0.4

0.8

1.2

1.6

Gro

wth

per

Cyc

le (

Å)

Purge after Al(CH3)

3 dose (s)

CVD+ALD ALD


Al(CH3)3

H2O

ALD cycle

Separated surface reactions

Precursor and reactants have to be very well evacuated/separated from the

reactor before pulsing the next precursorto avoid parasitic CVD

5


8 / 38

O2 plasma H2-N2 plasmaH2 plasma N2 plasma

Oxides and Metals Nitrides and Metals

Plasma-assisted ALD

O2 plasma

ALD cycle

Additional chemical reactivity

Range of reactive species from a plasmato provide additional reactivity to the

ALD surface chemistry


9 / 38Key features of ALD

(1) Ultimate control of film growth and thickness“digital” thickness control

(2) Relatively low substrate temperaturesdown to room temperature

(3) Extremely high conformality/step coverage self-limiting surface reactions

(4) Good uniformity on large substrates300 mm and even bigger

(5) Multilayer structures and nanolaminateseasy to alternate between processes

(6) Large set of materials and processesmany different materials demonstrated

6


10 / 38Key features ALD


11 / 38Thin films synthesized by ALD

RgDsMtHsBhSgDbRfAc**RaFr

RnAtPoBiO

PbS

TlHgTe

AuPtIrOsReWO,N,S,*

TaO,N

HfO,N,*

La*O,S,*

BaS

Cs

XeITeSbO

SnO

InO,N,S,*

CdS,Se,Te

AgPdRhRuO

TcMoN

NbO,N

ZrO,N,*

YO,S

SrO,S,*

Rb

KrBrSeAsGeO

GaO,N,*

ZnO,S,Te,Se

CuO,S

NiO

CoO

FeO

MnO,S,Te

CrO,*

VO

TiO,N,*

ScO

CaO,S,*

K

ArClSPO*

SiO,N,*

AlO,N,*

MgO,Te

Na

NeFONCBO,N,*

BeLi

HeH

181716151413121110987654321

LrNoMdFmEsCfBkCmAmPuNpUPaTh

LuO

YbTmO

ErO

HoO

DyO

TbGdO

EuO

SmO

PmNdO

PrO

CeOLanthanoids*

Actinoids**

Puurunen, J. Appl. Phys. 97, 121301 (2005)

7


12 / 38

ALD applications:Semiconductor industry (= key driver)

channel

source drain

gate oxide

(metal)gate

Metal-oxide-semiconductor field effect transistor (MOSFET)

Deposited high-k oxideThermally grown SiO2

DRAM deep trench capacitors

(aspect ratio up to 70)


13 / 38

ALD applications:Overview

Beneq

• Transistor gates stacks• Deep trench DRAM• High density capacitors• Hard disks• Interconnect technology• MEMS/Microsystems• Corrosion protection • Thin film encapsulation• Li+-batteries• Photonics• Photovoltaics• Displays • Solid-state lighting• Optical coatings• Nanotechnology• …

Sandia/

U. Colorado

Philips

Beneq

TU/e

+

- Philips

8


14 / 38

0.00

0.05

0.10

0.4

0.5

PE

-CV

D 1

00 n

m S

i 3N4

Rem

ote

plas

ma

ALD

20

nm A

l 2O3

WV

TR

(g⋅

m-2

⋅day

-1)

PEN

PE

-CV

D 1

00 n

m A

l 2O3

PE

-CV

D 1

00 n

m S

iO2

Al2O3/Ta2O5: x-ray mirrorSzeghalmi et al., Appl. Phys. Lett. 94, 133111 (2009)

TiO2/ZnS:Mn/TiO2 and TiO2: inverse opalsKing et al., Adv. Mater. 17, 1010 (2005)

a-SiNx:H filmNo film ALD Al2O3 film

Al2O3: encapsulation of organic LED

Langereis et al., Appl. Phys. Lett. 89, 081915 (2006)Groner et al., Appl. Phys. Lett. 88, 051907 (2006)Garcia et al., Appl. Phys. Lett. 89, 031915 (2006).

ALD applications:Ultrathin films – conformal growth – high material quality


15 / 38Outline





Electrical properties & electron scattering - Ultrahigh k dielectrics



Al2O3

Ta2O5

Er2O3

TiO2

TiNTaN Ta3N5

SrTiO3

PtRu

9


16 / 38

Measurement of the change in polarization of a light beam (at different wavelengths) upon reflection from a surface

Film thickness and optical dielectric function extracted by model-based analysis

In situ spectroscopic ellipsometry during ALD

J.A. Woollam Co. M2000-series:VIS + IR: 0.75 – 5.0 eVVIS + UV: 1.2 – 6.5 eV


17 / 38

ALD materials investigated Metal oxides – Metal nitrides - Metals

225 (100–225)15O2 plasmaTa[N(CH3)2]5Ta2O5

400 (300-400)8O2/O2 plasmaCpRu(CO)2C2H5Ru

300 (100-300)17O2/O2 plasma(CpCH3)Pt(CH3)3Pt

225 (150–250)37NH3 plasmaTa[N(CH3)2]5Ta3N5

225 (150–250)37H2 plasmaTa[N(CH3)2]5TaNx,x≤1

400 (100–400)40H2-N2 (10:1) plasmaTiCl4TiN

250 (150-350)>60O2 plasmaStar-Ti and Hyper-SrSrTiO3

300 (25–300)20O2 plasmaTi[OCH(CH3)2]4TiO2

300 (150–300)50O2 plasmaEr(thd)3Er2O3

290 (230–350)11O2 plasmaHf[N(CH3)(C2H5)]4HfO2

100 (25–300)4H2O/O2 plasmaAl(CH3)3Al2O3

Temperature(ºC)

Cycle time(s)

Reducing/ Oxidizing agent

Precursor gasMaterial

10


18 / 38

In situ spectroscopic ellipsometry (SE): Optical modeling of metal oxides

0

2

4

6

8

10

12

0

2

4

6

8

10

12

ε1

ε2

0

2

4

6

8

10

12

0

2

4

6

8

10

12

ε1

ε2

1 2 3 4 5 60

2

4

6

8

10

12

0

2

4

6

8

10

12

ε1

ε2

1 2 3 4 5 60

2

4

6

8

10

12

0

2

4

6

8

10

12

ε2

ε1

Die

lect

ric fu

nctio

ns

Photon energy (eV)

Al2O3 HfO2

Ta2O5 TiO2


19 / 38

In situ spectroscopic ellipsometry (SE): Optical modeling of metal nitrides

1 2 3 4 5 6-40

-30

-20

-10

0

10

20

0

10

20

30

40

50

60

ε1

ε2

1 2 3 4 5 60

2

4

6

8

10

12

0

2

4

6

8

10

12

ε1

ε2

1 2 3 4 5 6-40

-30

-20

-10

0

10

20

0

10

20

30

40

50

60

ε1

ε2

Die

lect

ric fu

nctio

ns

Photon energy (eV)

Ta3N5

TaNTiN

11


20 / 38

In situ spectroscopic ellipsometry (SE): Overview optical model parameters

See Topical Review: Langereis et al., J. Phys. D: Appl. Phys. 42, 073001 (2009)


21 / 38Outline








Al2O3

Ta2O5

Er2O3

TiO2

TiNTaN Ta3N5

SrTiO3

PtRu

12


22 / 38Characterize ALD film growth by in situ SE

Layer-by-layer film growth obtained by alternating ALD half-cycles- Linear growth with sub-monolayer control

0.37 Å (200 °C)

0.48 Å (100 °C)

0.56 Å (100 °C)

Growth rate

0.45 Å (200 °C)

0.80 Å (225 °C)

1.2 Å (100 °C)

Growth per cycle

TiN

TaN

Ta3N5

Metal nitride

TiO2

Ta2O5

Al2O3

Metal oxide

0

10

20

30

Al2O

3

Ta2O

5

TiO2

0 50 100 150 2000

5

10

15 Ta

3N

5

TaN TiN

Number of cycles

Film

thic

knes

s (n

m)

Thickness increases linear with number of cycles slope yields growth per cycle (GPC)


23 / 38

single deposition run yields saturation curves ex situ measurements not strictly necessary

Characterize ALD film growth by in situ SE

Layer-by-layer film growth obtained by alternating ALD half-cycles- Linear growth with sub-monolayer control

- Self-limiting chemistry essential for uniform and conformal growth

0 50 100 150 200 250 3000

4

8

12

16

20

Film

thic

knes

s (n

m)

Number of cycles

15 s

60 s

15 s

30 s

0 20 40 60 80 100 120 1400.00

0.02

0.04

0.06

0.08

0.10

Gro

wth

rat

e (n

m/c

ycle

)

Plasma exposure time (s)

single deposition run separate depositions

Monitor film thickness while changing precursor/reactant dosing time

13



Layer-by-layer film growth obtained by alternating ALD half-cycles- Linear growth with sub-monolayer control- Self-limiting chemistry essential for uniform and conformal growth

- Establish temperature window for true ALD growth

Plasma-assisted ALD using O2 plasma

0 50 100 150 200 250 3000.0

0.4

0.8

1.2

1.6

Al2O

3

Ta2O

5

TiO2

Gro

wth

per

cyc

le (

Å)

Substrate temperature (°C)

Ti[OCH(CH3)2]4

Ta[N(CH2)3]5

Al(CH3)3

Precursor

TiO2

Ta2O5

Al2O3

Metal oxide

Metal oxides can be deposited over a wide temperature range down to room temperature



Layer-by-layer film growth obtained by alternating ALD half-cycles- Linear growth with sub-monolayer control- Self-limiting chemistry essential for uniform and conformal growth- Establish temperature window for true ALD growth

- Insight into nucleation relevant for nanometer thick films targeted

0 50 100 150 2000

2

4

6

8

10

TaN on HF-last Si TiN on SiO

2 (1000 oC)

Film

thic

knes

s (n

m)

Number of cycles

0 50 100 150 200 250

0

2

4

6

8

10

12 Plasma ALD Pt Thermal ALD Pt

Thi

ckne

ss (

nm)

Number of cycles

Nucleation behavior can be investigated and film thickness can be controlled accurately

Knoops et al., Electrochem. Solid-State Lett. 12, G34 (2009)

14


26 / 38Characterize ALD with sub-monolayer sensitivity

Al2O3 Er2O3Er2O3 - Al2O3 nanolaminates Er-doped Al2O3 films

Er2O3

Alternating Al2O3 and Er2O3[Al precursor – O2 plasma]x – [Er precursor – O2 plasma]y

0.8 Å of Er2O3(24 cycles)

Bulky precursor

Al[(CH3)]3

3 Å of Al2O3(3 cycles)

Small precursor


27 / 38Outline








Al2O3

Ta2O5

Er2O3

TiO2

TiNTaN Ta3N5

SrTiO3

PtRu

15


28 / 38

Specifications for DRAM and decoupling capacitors:• High capacity density: > 500 nF/mm2

− Dielectric thickness: ~10-50 nm − High step coverage: > 95% for AR 20-30− Electrode thickness: 5-30 nm− Electrode conductivity: < 300 µΩcm

• Low leakage current (A/cm2)− Specs: ≤ 10-8 @ 1 V (DRAM)

• Low thermal budget− Specs: 400-600 °C

ALD for high-density capacitors

0

AC k

dε=

≤ 10-6 @ 3 V (Decap)

16


30 / 38

Resistivity:

2

0

1D

pu

ρε ω

Γ=

Metallic films — resistivity & electron MFP in TiN

100 150 200 250 300 350 4000

150

300

450

600

100 200 300 4000

1

2

3

4

5

6

7

in situ SE ex situ FPP

Res

istiv

ity (

µΩ

cm)

Cl c

onte

nt (

at.%

)

Resistivity increases with Cl-content

Langereis et al., J. Appl. Phys. 100, 023534 (2006)


31 / 38

( )

1/ 3

2/ 32

0

2*

3MFP

pu

Dm e

ωπ ε = Γ

*

20

2e pu

mN

e

εω

=

Resistivity:

2

0

1D

pu

ρε ω

Γ=

100 150 200 250 300 350 4000.0

0.2

0.4

0.6

0.8

1.0

0

1

2

3

4

5

6

Ele

ctro

n M

FP

(nm

)

Deposition temperature (°C)

Ele

ctro

n de

nsity

(10

22 c

m-3)

Metallic films — resistivity & electron MFP in TiN

100 150 200 250 300 350 4000

150

300

450

600

100 200 300 4000

1

2

3

4

5

6

7

in situ SE ex situ FPP

Res

istiv

ity (

µΩ

cm)

Cl c

onte

nt (

at.%

)

Resistivity increases with Cl-contentEspecially electron mean-free-path is

affected, electron density remains constant

Electron mean free path:

Langereis et al., J. Appl. Phys. 100, 023534 (2006)

Electron density:

18


34 / 38

• Composition control to optimize film propertiess

ALD SrTiO3 = x cycles ALD TiO2 + y cycles ALD SrO

• Crystalline films yield ultrahigh k valuess

Post-deposition anneal required for crystallization

Star Ti:[Me5Cp]Ti(OMe)3 = [(CH3

19


36 / 38ALD of SrTiO3 - crystallization

Post-deposition anneal of 30 nm thick SrTiO3 films ([Sr]/[Ti] = 1.3)

Film crystallization probed by in situ spectroscopic ellipsometry

Changing microstructure probed by dielectric function for TRTA ≥ 500 °C

Planar capacitors: k > 80 and leakage < 10-7 A/cm2 at 1 V


37 / 38Summary

In situ spectroscopic ellipsometry during ALD provides many merits:

• By monitoring the film thickness as a function of the number of cycles

the growth rate per cycle can be calculated during the ALD process

• ALD saturation curves can be obtained in a single deposition run

• Nucleation behavior can be studied on various substrates

• Sub-monolayer level surface changes can be probed

• Optical film properties can be obtained from the dispersion relation

• Electrical properties can be calculated from the Drude absorption in

metallic films

• Insight into crystalline phase and composition of the films can be

derived from the “shape” of the energy dispersion

Atomic layer deposition is an enabling technology for ultrathin film growth:

• sub-monolayer growth control with excellent conformality

• variety of materials at low deposition temperatures

20


38 / 38Acknowledgments

PlasmaPlasmaPlasmaPlasma----assisted assisted assisted assisted

atomic layer depositionatomic layer depositionatomic layer depositionatomic layer deposition

an in situ diagnostic study

Erik Langereis

Digital copy available at TU/e library(http://www.tue.nl/bib)

PhD thesis

Plasma & Materials Processing (PMP)• Dr. Stephan Heil• Hans van Hemmen• Harm Knoops• Adrie Mackus• Jeroen Keijmel• Menno Bouman• Dr. Erwin Kessels• Prof. Dr. Richard van de Sanden

Dutch technology foundation

in situ spectroscopic ellipsometry as a versatile tool to ... · 2 / department of applied physics...

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