atomic layer depositionatomic layer deposition (ald) · th per cycle cvd subsaturation cvd l 020 e)...

Atomic Layer DepositionAtomic Layer Deposition(ALD)

Erwin Kessels

[email protected]/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 / t2. High conformality/step coverage

3. Good uniformity on large substrates

4. Low substrate temperatures


Very demanding applications

Nanoelectronics Photovoltaics

fProtective thin films Flexible electronics


CMOS scaling in nanoelectronics

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Active Area

Gate FieldSpacers

Active Area

Gate FieldSpacers

Active Area

Gate FieldSpacers

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Gate FieldSpacers

Active Area

Gate FieldSpacers

Active Area

Gate FieldSpacers

Ge/IIIVGe/IIIV

nanowiresnanowires

g pg p

HfO

metal gatemetal gate

FinFETFinFET

L=35nm

SiGe

L=35nmL=35nm

SiGe

strainstrain

HfO 2high high --

timesilicidesilicide

USJUSJ

Timee

Courtesy of Marc Heyns, IMEC/Applied Physics - Erwin Kessels

Field-effect transistor: replacing SiO2 by HfO2

32 nm

Thermally grown SiO2Thermally grown SiO2


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


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


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


ALD of Al2O3 films: Al(CH3)3 - H2O process


Thickness vs. number of cycles

Film thickness is ruledby the number of cycles chosen

30

1. Al(CH3)3

2 SiH {N(C H )}

H3C AlCH3

CH3

N(C2H5)2 301. Al2O3

2. SiO2

3. Ta2O5m)

2. SiH2{N(C2H5)}2

3 T {N(CH ) }N(CH3)2

SiH H

N(C2H5)2

202 5

4. ZnO2

5. TiO2ne

ss (n

m3. Ta{N(CH3)2}5(H3C)2N Ta

N(CH3)2

N(CH3)2

( 3)2

N(CH3)2

10

Thic

kn

4. Zn(CH2CH3)2H3C

H2C

Zn

H2C

CH3

0 50 100 150 200 2500

ALD C l

5. Ti(Cp*)(OCH3)3

TiH3CO OC

OCH3

H3CCH3

CH3

H3C CH3

+

/Applied Physics - Erwin KesselsPotts et al., J. Electrochem. Soc., 157, P66 ( 2010).Dingemans et al., J. Electrochem. Soc. 159, H277 (2012)

ALD CyclesH3CO OCH3+ H2O, O3, or O2 plasma

Key features of ALD

1. Control of film growth and thickness‘Digital’ thickness control

2. High conformality/step coverageSelf-limiting surface reactions

3 G d if it l b t t3. Good uniformity on large substrates300 mm and even bigger

4. Low substrate temperaturespBetween 25 - 400 °C

5. Multilayer structures and nanolaminatesEasy to alternate between processes

6. Large set of materials and processesMany different materials demonstratedMany different materials demonstrated


Line-of-sight vs. conformal growth


Materials deposited ALD

/Applied Physics - Erwin KesselsPuurunen, J. Appl. Phys. 97, 121301 (2005)Miikkulainen et al., J. Appl. Phys. 113, 021301 (2013).

Outline


2. ALD equipment





Single wafer 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)


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 challengingg p g g

• Applications: semiconductor (memory), displays,

solar cells, etc.


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 times4. More versatility/freedom in process and materials etc.

Direct plasmaSubstrate part of plasma creation zone

Remote plasmaSubstrate “downstream” of plasma creation

zone

/Applied Physics - Erwin KesselsHeil 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 AlCH3

CH3

Si

N(C2H5)2

2 0 Al2O3 TiO2 - Ti(OiPr)4

e)

SiH2{N(C2H5)}2

3.Ta{N(CH3)2}5 (H3C)2N Ta

(C )

N(CH3)2

N(CH3)2

SiH H

N(C2H5)2

1.6

2.0 2 3 2 ( )4

SiO2 TiO2 - Ti(CpMe)(OiPr)3

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

e (Å

/cyc

le

( 3)2 5

4.Ti(OiPr)4

N(CH3)2N(CH3)2

Ti i

OiPr0.8

1.2

per C

ycle

4

5.Ti(CpMe)(OiPr)3 Ti

TiiPrO OiPr

OiPr

CH3

0 0

0.4G

row

th

3

6.Ti(Cp*)(OCH )

TiiPrO OiPr

OiPr

H3CCH3

CH3

0 50 100 150 200 250 3000.0

Substrate Temperature (°C)


Ti(Cp*)(OCH3)3Ti

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


ALD equipment suppliers (incomplete list)

Semiconductor Solar / R2RR&D / Pilot


Outline


2. ALD equipment





Metalorganic and H2O: ligand exchange (Al2O3)

Al(CH3)3 exposure Purge

10-8

H Ory s

igna

l (A)

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

H2O

H2O

H2O

H2O

10-8

H Ory s

igna

l (A)

10-8

H Ory s

igna

l (A)

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

H2O

H2O

H2O

H2O

10-10

10-9H2O

spec

trom

etr

CH410-10

10-9H2O

spec

trom

etr

CH410-10

10-9H2O

spec

trom

etr

CH4AlOH*+ Al(CH3)3 AlOAl(CH3)2* + CH4

Cycle0 25 50 75 100

10-11Mas

s

Time (s)

4

0 25 50 75 10010-11M

ass

Time (s)

4

0 25 50 75 10010-11M

ass

Time (s)

4AlOH Al(CH3)3 AlOAl(CH3)2 CH4

Surface chemistry rules ALD process:

ligand exchange between Al(CH ) and

AlOH* + CH4AlCH3* + 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 exposurePurge/Applied Physics - Erwin Kessels



10-8

H Ory s

igna

l (A)

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

H2O

H2O

H2O

H2O

10-8

H Ory s

igna

l (A)

10-8

H Ory s

igna

l (A)

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

Al(C

H3)

3

H2O

H2O

H2O

H2O

10-10

10-9H2O

spec

trom

etr

CH410-10

10-9H2O

spec

trom

etr

CH410-10

10-9H2O

spec

trom

etr

CH4

Cycle0 25 50 75 100

10-11Mas

s

Time (s)

4

0 25 50 75 10010-11M

ass

Time (s)

4

0 25 50 75 10010-11M

ass

Time (s)

4


ligand exchange between Al(CH ) andligand exchange between Al(CH3)3 and –OH surface groups and H2O and –CH3

surface groups leads to CH4 reaction products

H2O exposurePurge/Applied Physics - Erwin Kessels


4x10-5

rban

ce

2940 cm-1 1207 cm-1

Al(CH3)3chemisorption


frare

d ab

so OH stretching

CHxstretching

CHxdeformation

2940 cm 1 1207 cm 1

H O

4000 3500 3000 2500 2000 1500 1000

In

Wavenumber (cm-1)

H2Oexposure

Cycle


Surface alternately covered by –OHSurface alternately covered by –OH surface groups and –CH3 surface groups


H2O exposurePurge


0.8

1.2

Cyc

le (Å

)Al(CH3)3 exposure Purge

0.4

owth

per

C

0 20 40 600.0

Gro

Al(CH3)3 dose (ms)Cycle

Conditions such that precursors react through saturative surface reactions:

Al(CH3)3 does not react with –CH3surface groups


H2O exposurePurge


0 8

1.2

ycle

(Å)Al(CH3)3 exposure Purge

0.4

0.8

wth

per

Cy

0 20 40 60 800.0G

row

H2O dose (ms)Cycle

Conditions such that precursors react through saturative surface reactions:

H2O does not react with –OH surface groups


H2O exposurePurge


1.2

1.6

cle

(Å)


0.4

0.8

wth

per

Cyc

CVD+ALD ALD

0 2 4 6 80.0G

row

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


H2O exposurePurge

ALD process: saturation curves (Al2O3)

(a)

0.15

0.20

(nm

/cyc

le) Thermal ALD - Al(CH3)3 & H2O

0.05

0.10

wth

per

Cyc

le (

CVDSubsaturation CVD

0 20le) (b)

0 20 40 60 80 1000.00G

row

Dose time (ms)0 1 2 3 4 5

Purge time (s)0 20 40 60 80

H2O dose (ms)0 1 2 3

Purge time (s)Plasma ALD - Al(CH3)3 & O2 plasma

0.10

0.15

0.20

Cyc

le (n

m/c

ycl

Subsaturation

0 20 40 60 80 1000.00

0.05

Gro

wth

per

C

0 1 2 3 4 5 0 1 2 3 4 5 0 1 2 3

CVD


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 (n

m/c

ycle

(a)

0.0

0.1

Gro

wth

rate

3456

(b)

per

cyc

le

cm-2)

0123

# A

l ato

ms

(10

15 c

0 100 200 300 4000

Substrate temperature (oC)

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


( 3)3 ( 3)2 4

AlOH* + CH4AlCH3* + 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. CondensationB InsufficientWindow

Cyc

le A C

AC

B. Insufficient thermal energy

C. CVD

wth

per

C

B

D. Evaporation

H2O

Gro

w B DBD OH OH O∆T

Substrate Temperature Substrate/film surface


Metal halide: ligand exchange (HfO2 and TiN)

HfOH* + HfCl HfOHfCl * + HCl

Metal oxides: ligand exchange

HfOH* + HfCl4 HfOHfCl3* + HCl

HfOH* + HClHfCl* + H2O

TiNH* + TiCl TiNTiCl * + HCl

Metals nitrides: ligand exchange

TiNH + TiCl4 TiNTiCl3 + HCl

TiNH2* + HClTiCl* + NH3

/Applied Physics - Erwin Kessels * 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 H2O2 (MeCp)PtMe2* + 24 O2Pt

Metals: fluorosilane elimination reactions

WSiF H* + WF WWF * + SiF HWSiF2H + WF6 WWF5 + SiF3H

WSiF2H* + SiF3H + 2H2WWF5* + Si2H6


Plasma-based chemistry (Al2O3 and TiN)

Metal oxides: combustion

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

AlOH* + CO2 + H2OAlCH3* + 4O

Metal nitrides: ligand exchange and reduction

TiNH* + TiCl TiNTiCl * + HClTiNH + TiCl4 TiNTiCl3 + HCl

TiNH2* + HClTiCl* + 3H + N


ALD of doped films, ternary compounds, etc.


ALD of Al-doped ZnO films

Zn(C2H5)2 + H2O ZnO + 2 C2H6ZnO

ZnO:Al n cycles ZnO + m cycles Al2O3

101

150 ºC

Al2O3 TMA or DMAI + H2O

100

TMA

c

m)

2

10-1

sist

ivity (

0 5 10 15 20 25 3010-3

10-2

Res

DMAI

/Applied Physics - Erwin Kessels Wu et al., J. Appl. Phys. 114, 024308 (2013)

0 5 10 15 20 25 30

Al fraction (at.%)

Outline


2. ALD equipment





Thin-film electroluminescent (TFEL) displays

New large-area display in 1983

Atomic layer deposited ZnS:Mn

1974 First patent on ALD filed by Tuomo Suntala1983 Introduction of first ALD (non)-transparent inorganic TFEL display

Since 1989 Commercial production of ALD-TFEL displays by Planar

/Applied Physics - Erwin Kessels 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 KesselsLangereis 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, USA)

ALD films for photovoltaics

CIGS solar cells Dye-sensitizedsolar cells

c-Si solar cellsOrganic solar cells

Buffer layers

Zn(O S)

Barrier layer

Al O HfO

Surfacepassivation

Transparent conductive oxide

On the verge of

Zn(O,S)(Zn,Mg)O

In2O3

l

Al2O3, HfO2, TiO2, etc.

PhotoanodeZ O S O

pAl2O3ZnO:Al

Electron selective layer

industrial application

High-throughput equipment

Encapsulation

Al2O3

ZnO, SnO2, TiO2, etc.

Blocking layer Encapsulation

Al2O3, ZnO, TiO2

selective layer

/Applied Physics - Erwin Kessels Van Delft et al., Semicond. Sci. Technol. 27, 074002 (2012).

q pavailable

g y

HfO2, SnO2, TiO2

pAl2O3

Outline


2. ALD equipment





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

bwww.beneq.com


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.


www.asm.com www.beneq.com

Spatial ALD concept

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


Spatial ALD: S2S and R2R

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

M i 1www.levitech.nl

Movie 1

Movie 2

• Roll-to-roll (R2R)

www.solaytec.com

Movie 2

www.lotusat.com www.beneq.comwww.tno.nlMovie 3


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 techniques2. 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 launched9. Equipment for batch ALD and S2S and R2R spatial ALD launched

10. ALD has a bright future


Further reading and downloads

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

Recent literature on ALD for PVRecent literature on ALD for PV• Van Delft et al., Semicond. Sci. Technol. 27 074002 (2012)• Bakke et al., Nanoscale 3, 3482 (2011)


Title

/Department of Applied Physics

atomic layer depositionatomic layer deposition (ald) · th per cycle cvd subsaturation cvd l 020 e)...

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