Atomic Layer Deposition Atomic Layer Deposition (ALD) Erwin - - PowerPoint PPT Presentation

Atomic Layer Deposition Atomic Layer Deposition (ALD)

Erwin Kessels

w.m.m.kessels@tue.nl www.phys.tue.nl/pmp

Vapor phase deposition technologies

Physical Vapor Deposition (PVD) – sputtering – Chemical Vapor Deposition (CVD)

Energetic ions! Heat!

/Applied Physics - Erwin Kessels

g

More applications have stricter requirements on

1. Precise growth and thickness control 2 Hi h f lit / t 2. High conformality/step coverage 3. Good uniformity on large substrates 4. Low substrate temperatures

/Applied Physics - Erwin Kessels

Very demanding applications

Nanoelectronics Photovoltaics f Protective thin films Flexible electronics

/Applied Physics - Erwin Kessels

CMOS scaling in nanoelectronics

??? ??? graphene graphene

??? ??? ??? ???

Ge/IIIV Ge/IIIV nanowires nanowires g p g p

HfO

metal gate metal gate FinFET FinFET

L=35nm

SiGe

L=35nm L=35nm

SiGe

strain strain

HfO 2

high high -

• 

time

silicide silicide USJ USJ

Time

Courtesy of Marc Heyns, IMEC

/Applied Physics - Erwin Kessels

Field-effect transistor: replacing SiO2 by HfO2

32 nm Thermally grown SiO2 Thermally grown SiO2

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Precise deposition of nanometer-thick Hf-based oxides

www.chipworks .com

Field-effect transistor: going from 2D to 3D gates

22 nm Precise deposition of nanometer-thick Hf-based oxides with excellent conformality

/Applied Physics - Erwin Kessels

with excellent conformality

www.chipworks .com

Outline

1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD

/Applied Physics - Erwin Kessels

Atomic Layer Deposition (ALD)

• Reactants (precursors) are pulsed into reactor alternately and cycle-wise (ABAB..)
• Precursors react through saturative (self-limiting) surface reactions
• A sub-monolayer of material deposited per cycle

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ALD of Al2O3 films: Al(CH 3)3 - H 2O process

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Thickness vs. number of cycles

Film thickness is ruled by the number of cycles chosen 30

• 1. Al(CH3)3

2 S

iH {N(C H )}

H3C Al CH3 CH3 N(C2H5)2

30

1. Al2O3 2. SiO2 3. Ta2O5

m)

• 2. S

iH2{N(C2H5)}2 3 T {N(CH ) }

N(CH3)2 Si H H N(C2H5)2

20

2 5

4. ZnO2 5. TiO2

ness (nm

• 3. Ta{N(CH3)2}5

(H3C)2N Ta N(CH3)2 N(CH3)2 (

3)2

N(CH3)2

10

Thickn

• 4. Zn(CH2CH3)2

H3C H2 C Zn H2 C CH3

50 100 150 200 250

ALD C l

• 5. Ti(Cp*)(OCH3)3

Ti H3CO OC OCH3 H3C CH3 CH3 H3C CH3

+

/Applied Physics - Erwin Kessels

Potts et al., J. Electrochem. Soc., 157, P66 ( 2010). Dingemans et al., J. Electrochem. Soc. 159, H277 (2012)

ALD Cycles

H3CO OCH3

+

H2O, O3, or O2 plasma

Key features of ALD

1. Control of film growth and thickness ‘Digital’ thickness control 2. High conformality/step coverage Self-limiting surface reactions 3 G d if it l b t t 3. Good uniformity on large substrates 300 mm and even bigger 4. Low substrate temperatures p Between 25 - 400 °C 5. Multilayer structures and nanolaminates Easy to alternate between processes 6. Large set of materials and processes Many different materials demonstrated Many different materials demonstrated

/Applied Physics - Erwin Kessels

Line-of-sight vs. conformal grow th

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Materials deposited ALD

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Puurunen, J. Appl. Phys. 97, 121301 (2005) Miikkulainen et al., J. Appl. Phys. 113, 021301 (2013).

Outline

1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD

/Applied Physics - Erwin Kessels

Single w afer ALD reactor

Shower head reactor (warm or hot wall reactor) Flow-type reactor (hot wall reactor)

• Temporal ALD

P l t i f

• Pulse-train of precursors
• Reactor pressure 1-10 Torr
• Applications: semiconductor (logic)

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pp ( g )

Batch ALD reactor

Temporal ALD

Batch reactor

• Temporal ALD
• Typically 50-500 substrates in a single deposition run
• Single-side deposition can be challenging

g p g g

• Applications: semiconductor (memory), displays,

solar cells, etc.

/Applied Physics - Erwin Kessels

Plasma ALD reactors

Plasma-assisted ALD can yield additional benefits for specific applications: 1. Improved material properties 2. Deposition at lower temperatures (also room temperature) Direct plasma Remote plasma p p ( p ) 3. Higher growth rates/cycle and shorter cycle times 4. More versatility/freedom in process and materials etc. Direct plasma Substrate part of plasma creation zone Remote plasma Substrate “downstream” of plasma creation zone

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Heil et al., J. Vac. Sci. Technol. A 25, 1357 (2007). Profijt et al., J. Vac. Sci. Technol. A 29 050801 (2011)

Plasma-based chemistry (metal oxides)

1. Al(CH3)3

2.

H3C Al CH3 CH3 Si N(C2H5)2

2 0

Al2O3 TiO2 - Ti(O

iPr)4

e)

SiH2{N(C2H5)}2 3. Ta{N(CH3)2}5

(H3C)2N Ta (C ) N(CH3)2 N(CH3)2 Si H H N(C2H5)2

1.6 2.0

2 3 2

( )4 SiO2 TiO2 - Ti(Cp

Me)(O iPr)3

Ta2O5 TiO2 - Ti(Cp*)(OMe)3

e (Å/cycle

(

3)2 5

4. Ti(OiPr)4

N(CH3)2 N(CH3)2 Ti

i

OiPr

0.8 1.2

per Cycle

4

5. Ti(CpMe)(OiPr)3

Ti Ti

iPrO

OiPr OiPr CH3

0 0 0.4

Growth

3

6. Ti(Cp*)(OCH )

Ti

iPrO

OiPr OiPr H3C CH3 CH3

50 100 150 200 250 300 0.0

Substrate Temperature (°C)

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Ti(Cp*)(OCH3)3

Ti H3CO OCH3 OCH3 H3C CH3

Potts et al., J. Electrochem. Soc., 157, P66 ( 2010). Dingemans et al., J. Electrochem. Soc. 159, H277 (2012)

Oxford Instruments OpAL reactor – Plasma ALD

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ALD equipment suppliers (incomplete list)

Semiconductor Solar / R2R R& D / Pilot

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Outline

1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD

/Applied Physics - Erwin Kessels

Metalorganic and H 2O: ligand exchange (Al2O3)

Al(CH3)3 exposure Purge

10

• 8

H O ry signal (A)

Al(CH3)3 Al(CH3)3 Al(CH3)3 Al(CH3)3 H2O H2O H2O H2O

10

• 8

H O ry signal (A)

10

• 8

H O ry signal (A)

Al(CH3)3 Al(CH3)3 Al(CH3)3 Al(CH3)3 H2O H2O H2O H2O

10

• 10

10

• 9

H2O spectrometr CH4

10

• 10

10

• 9

H2O spectrometr CH4

10

• 10

10

• 9

H2O spectrometr CH4

AlOH*+ Al(CH3)3 AlOAl(CH3)2* + CH4

Cycle

25 50 75 100 10

• 11

Mass Time (s)

4

25 50 75 100 10

• 11

Mass Time (s)

4

25 50 75 100 10

• 11

Mass Time (s)

4

AlOH Al(CH3)3 AlOAl(CH3)2 CH4

Surface chemistry rules ALD process: ligand exchange between Al(CH ) and

AlOH* + CH4 AlCH3* + H2O

ligand exchange between Al(CH3)3 and –OH surface groups and H2O and –CH3 surface groups leads to CH4 reaction products

* are surface species

H2O exposure Purge

/Applied Physics - Erwin Kessels

Metalorganic and H 2O: ligand exchange (Al2O3)

Al(CH3)3 exposure Purge

10

• 8

H O ry signal (A)

Al(CH3)3 Al(CH3)3 Al(CH3)3 Al(CH3)3 H2O H2O H2O H2O

10

• 8

H O ry signal (A)

10

• 8

H O ry signal (A)

Al(CH3)3 Al(CH3)3 Al(CH3)3 Al(CH3)3 H2O H2O H2O H2O

10

• 10

10

• 9

H2O spectrometr CH4

10

• 10

10

• 9

H2O spectrometr CH4

10

• 10

10

• 9

H2O spectrometr CH4

Cycle

25 50 75 100 10

• 11

Mass Time (s)

4

25 50 75 100 10

• 11

Mass Time (s)

4

25 50 75 100 10

• 11

Mass Time (s)

4

Surface chemistry rules ALD process: ligand exchange between Al(CH ) and ligand exchange between Al(CH3)3 and –OH surface groups and H2O and –CH3 surface groups leads to CH4 reaction products

H2O exposure Purge

/Applied Physics - Erwin Kessels

Metalorganic and H 2O: ligand exchange (Al2O3)

4x10

• 5

rbance

2940 cm-1 1207 cm-1

Al(CH3)3 chemisorption

Al(CH3)3 exposure Purge frared abso

OH stretching CHx stretching CHx deformation 2940 cm 1 1207 cm 1

H O

4000 3500 3000 2500 2000 1500 1000

In Wavenumber (cm

• 1)

H2O exposure

Cycle

Surface chemistry rules ALD process: Surface alternately covered by –OH Surface alternately covered by –OH surface groups and –CH3 surface groups

/Applied Physics - Erwin Kessels

H2O exposure Purge

Metalorganic and H 2O: ligand exchange (Al2O3)

0.8 1.2

Cycle (Å)

Al(CH3)3 exposure Purge

0.4

• wth per C

20 40 60 0.0

Gro Al(CH3)3 dose (ms)

Cycle

Conditions such that precursors react through saturative surface reactions: Al(CH3)3 does not react with –CH3 surface groups

/Applied Physics - Erwin Kessels

H2O exposure Purge

Metalorganic and H 2O: ligand exchange (Al2O3)

0 8 1.2

ycle (Å)

Al(CH3)3 exposure Purge

0.4 0.8

wth per Cy

20 40 60 80 0.0

Grow H2O dose (ms) Cycle

Conditions such that precursors react through saturative surface reactions: H2O does not react with –OH surface groups

/Applied Physics - Erwin Kessels

H2O exposure Purge

Metalorganic and H 2O: ligand exchange (Al2O3)

1.2 1.6

cle (Å)

Al(CH3)3 exposure Purge

0.4 0.8

wth per Cyc

CVD+ALD ALD 2 4 6 8 0.0

Grow Purge after Al(CH3)3 dose (s) Cycle

Precursors and reactants should be very well evacuated/separated from reactor before pulsing the next precursor/reaction: Otherwise parasitic CVD

/Applied Physics - Erwin Kessels

H2O exposure Purge

ALD process: saturation curves (Al2O3)

(a)

0.15 0.20

(nm/cycle)

Thermal ALD - Al(CH3)3 & H2O

0.05 0.10

wth per Cycle (

CVD

Subsaturation

CVD

0 20

le)

(b)

20 40 60 80 100

0.00

Grow

Dose time (ms)

1 2 3 4 5

Purge time (s)

20 40 60 80

H2O dose (ms)

1 2 3

Purge time (s)

Plasma ALD - Al(CH3)3 & O2 plasma

0.10 0.15 0.20

Cycle (nm/cycl Subsaturation

20 40 60 80 100

0.00 0.05

Growth per C

1 2 3 4 5 1 2 3 4 5 1 2 3

CVD

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Dose time (ms) Purge time (s) Plasma time (s) Purge time (s)

ALD process: substrate temperature (Al2O3)

e)

0.2

Plasma ALD Thermal ALD e (nm/cycle

(a) 0.0 0.1

Growth rate

3 4 5 6 (b)

per cycle cm

• 2)

1 2 3

# Al atoms (10

15 c

100 200 300 400

Substrate temperature (

• C)

AlOH* + Al(CH3)3 AlOAl(CH3)2* + CH4

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(

3)3

(

3)2 4

AlOH* + CH4 AlCH3* + H2O

Van Hemmen et al., J. Electrochem. Soc. 154, G165 (2007) Potts et al., J. Electrochem. Soc., 157, P66 ( 2010).

ALD process: substrate temperature (ideal case)

ALD Temperature Window



• A. Condensation

B Insufficient

Window

Cycle 

A C A C

• B. Insufficient

thermal energy

• C. CVD

wth per C

B

• D. Evaporation

H2O

Grow

B D B D

OH OH O ∆T

Substrate Temperature 

Substrate/film surface

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Metal halide: ligand exchange (HfO2 and TiN)

HfOH* + HfCl HfOHfCl * + HCl Metal oxides: ligand exchange HfOH* + HfCl4 HfOHfCl3* + HCl HfOH* + HCl HfCl* + H2O TiNH* + TiCl TiNTiCl * + HCl Metals nitrides: ligand exchange TiNH + TiCl4 TiNTiCl3 + HCl TiNH2* + HCl TiCl* + NH3

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* are surface species

Metals: combustion (Pt) and reduction (W)

Noble metals: combustion by chemisorbed O2 3 O* + 2 (MeCp)PtMe3 2 (MeCp)PtMe2* + CH4 + CO2 + H2O 2 Pt* + 3 O* + 16 CO2 + 13 H2O 2 (MeCp)PtMe2* + 24 O2

Pt

Metals: fluorosilane elimination reactions WSiF H* + WF WWF * + SiF H WSiF2H + WF6 WWF5 + SiF3H WSiF2H* + SiF3H + 2H2 WWF5* + Si2H6

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* are surface species

Plasma-based chemistry (Al2O3 and TiN)

Metal oxides: combustion AlOH*+ Al(CH3)3 AlOAl(CH3)2* + CH4 AlOH* + CO2 + H2O AlCH3* + 4O Metal nitrides: ligand exchange and reduction TiNH* + TiCl TiNTiCl * + HCl TiNH + TiCl4 TiNTiCl3 + HCl TiNH2* + HCl TiCl* + 3H + N

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* are surface species

ALD of doped films, ternary compounds, etc.

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ALD of Al-doped ZnO films

Zn(C2H5)2 + H2O ZnO + 2 C2H6 ZnO ZnO:Al

n cycles ZnO + m cycles Al2O3

10

1

150 ºC Al2O3 TMA or DMAI + H2O

10 TMA

cm)

2

10

• 1

sistivity (

5 10 15 20 25 30 10

• 3

10

• 2

Res

DMAI

/Applied Physics - Erwin Kessels

Wu et al., J. Appl. Phys. 114, 024308 (2013)

5 10 15 20 25 30

Al fraction (at.%)

Outline

1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD

/Applied Physics - Erwin Kessels

Thin-film electroluminescent (TFEL) displays

New large-area display in 1983

Atomic layer deposited ZnS:Mn 1974 First patent on ALD filed by Tuomo Suntala 1983 Introduction of first ALD (non)-transparent inorganic TFEL display Since 1989 Commercial production of ALD-TFEL displays by Planar

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• T. Suntola, Mater. Sci. Rep. 4, 261 (1989)

Encapsulation of OLED Devices

No encapsulation Thin-film-encapsulated OLEDs after testing 40 nm ALD Al2O3 film

Thin film encapsulation requires:

• low deposition temperatures
• low water vapor transmission rates
• low pinhole (black spot) density

/Applied Physics - Erwin Kessels

Langereis et al., Appl. Phys. Lett. 89, 081915 (2006). Keuning et al., J. Vac. Sci. Technol. A 30, 01A131 (2012).

Defect (dust particle) encapsulation

/Applied Physics - Erwin Kessels Courtesy of Jian Jim Wang (NanoNuvo Corporation, US A)

ALD films for photovoltaics

CIGS solar cells Dye-sensitized solar cells c-Si solar cells Organic solar cells Buffer layers Zn(O S ) Barrier layer Al O HfO Surface passivation Transparent conductive oxide On the verge of Zn(O,S ) (Zn,Mg)O In2O3 l Al2O3, HfO2, TiO2, etc. Photoanode Z O S O p Al2O3 ZnO:Al Electron selective layer industrial application High-throughput equipment Encapsulation Al2O3 ZnO, S nO2, TiO2, etc. Blocking layer Encapsulation Al2O3, ZnO, TiO2 selective layer

/Applied Physics - Erwin Kessels

Van Delft et al., S

• emicond. S
• ci. Technol. 27, 074002 (2012).

q p available g y HfO2, S nO2, TiO2 p Al2O3

Outline

1. Atomic layer deposition (ALD): basics and key features 2. ALD equipment 3. Materials & ALD surface chemistries 4. Some applications of ALD 5. Recent developments in high-throughput ALD

/Applied Physics - Erwin Kessels

Large substrate ALD reactors

• Temporal ALD
• Can be (inline) single wafer or batch reactor
• Substrate size up to 120 x 120 cm2
• Applications: Thin-film transistors, encapsulation,

CIGS solar cells, transparent conductive oxides

b w w w .beneq.com

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Batch ALD reactor

• Temporal ALD
• Typically 50-500 substrates in a single deposition run
• Single-side deposition can be challenging
• Applications: semiconductor (memory), displays,

Applications: semiconductor (memory), displays, solar cells, etc.

/Applied Physics - Erwin Kessels

w w w .asm.com w w w .beneq.com

Spatial ALD concept

• Precursor and reactant pulsing occur at different positions
• The substrate or the “ALD deposition head” must move

The substrate or the ALD deposition head must move

• Purge areas created by inert gas barriers prevent CVD reactions

 requires operation at high pressure

• No gas switching or vacuum pumps no deposition on the reactor walls
• No gas switching or vacuum pumps, no deposition on the reactor walls

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Spatial ALD: S2S and R2R

• Sheet-to-sheet (S2S, or wafer-to-wafer)

M i 1

w w w .levitech.nl

Movie 1 Movie 2

• Roll-to-roll (R2R)

w w w .solaytec.com

Movie 2

w w w .lotusat.com w w w .beneq.com w w w .tno.nl

Movie 3

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Summary

1. ALD can fulfill stricter requirements on thin film growth in terms of growth control, conformality, uniformity and low temperature 2 ALD is therefore complementary to PVD and CVD techniques 2. ALD is therefore complementary to PVD and CVD techniques 3. ALD relies on surface chemistry – not all materials can be prepared 4. ALD cycle yields sub-monolayer of film (typically 0.5 – 1 Å/ cycle) ( ) 5. ALD is gaining popularity also outside semiconductor industry 6. Runner up (method): Plasma ALD 7. Runner up (application): ALD for photovoltaics 8. High-volume manufacturing equipment is available 9 Equipment for batch ALD and S2S and R2R spatial ALD launched 9. Equipment for batch ALD and S2S and R2R spatial ALD launched

• 10. ALD has a bright future

/Applied Physics - Erwin Kessels

Further reading and dow nloads

Recent literature on ALD

• Book on ALD, Pinna and Knez (Eds.) Wiley VHC (2011)

, ( ) y ( )

• Kessels and Putkonen, MRS Bull. 36, 907 (2011)

Recent literature on plasma ALD p

• Profijt et al., J. Vac. Sci. Technol. A 29 050801 (2011)

Recent literature on ALD for PV Recent literature on ALD for PV

• Van Delft et al., Semicond. Sci. Technol. 27 074002 (2012)
• Bakke et al., Nanoscale 3, 3482 (2011)

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Title

/Department of Applied Physics