ALD_Kessels.pdf

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

Very demanding applications
Nanoelectronics Photovoltaics
f
Protective thin films Flexible electronics

CMOS scaling in nanoelectronics
???
???
graphene
graphene
ActiveArea
Gate Field
Spacers
ActiveArea
Gate Field
Spacers
ActiveArea
Gate Field
Spacers
???
???
???
???
ActiveArea
Gate Field
Spacers
ActiveArea
Gate Field
Spacers
ActiveArea
Gate Field
Spacers
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
e
Courtesy of Marc Heyns, IMEC

Field-effect transistor: replacing SiO2 by HfO2
32 nm
Thermally grown SiO2
Thermally 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 ruled
by the number of cycles chosen
30
1. Al(CH3)3
2 SiH {N(C H )}
H3C Al
CH3
CH3
N(C2H5)2
30
1. Al2
O3
2. SiO2
3. Ta2
O5
m)
2. SiH2{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
0 50 100 150 200 250
0
ALD C l
5. Ti(Cp*)(OCH3)3
Ti
H3CO
OC
OCH3
H3C
CH3
CH3
H3C CH3
+
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

Line-of-sight vs. conformal growth

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

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 challenging
g 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 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
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 Al2
O3
TiO2
- Ti(O
i
Pr)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
i
Pr)3
Ta2
O5
TiO2
- Ti(Cp*)(OMe)3
e
(Å/cycle
( 3)2 5
4.
Ti(OiPr)4
N(CH3)2
N(CH3)2
Ti i
Oi
Pr
0.8
1.2
per
Cycle
4
5.
Ti(CpMe)(OiPr)3 Ti
Ti
i
PrO
Oi
Pr
Oi
Pr
CH3
0 0
0.4
Growth
3
6.
Ti(Cp*)(OCH )
Ti
i
PrO
Oi
Pr
Oi
Pr
H3C
CH3
CH3
0 50 100 150 200 250 300
0.0
Substrate Temperature (°C)
Ti(Cp*)(OCH3)3
Ti
H3CO
OCH3
OCH3
H3C CH3
Dingemans et al., J. Electrochem. Soc. 159, H277 (2012)

Oxford Instruments OpAL reactor – Plasma ALD

ALD equipment suppliers (incomplete list)
Semiconductor Solar / R2R
R&D / Pilot

Metalorganic and H2O: ligand exchange (Al2O3)
Al(CH3)3 exposure Purge
10
-8
H O
ry
signal
(A)
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
H
2
O
H
2
O
H
2
O
H
2
O
10
-8
H O
ry
signal
(A)
10
-8
H O
ry
signal
(A)
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
H
2
O
H
2
O
H
2
O
H
2
O
10
-10
10
-9
H2
O
spectrometr
CH4
10
-10
10
-9
H2
O
spectrometr
CH4
10
-10
10
-9
H2
O
spectrometr
CH4
AlOH*+ Al(CH3)3 AlOAl(CH3)2* + CH4
Cycle
0 25 50 75 100
10
-11
Mass
Time (s)
4
0 25 50 75 100
10
-11
Mass
Time (s)
4
0 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

10
-8
H O
ry
signal
(A)
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
H
2
O
H
2
O
H
2
O
H
2
O
10
-8
H O
ry
signal
(A)
10
-8
H O
ry
signal
(A)
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
Al(CH
3
)
3
H
2
O
H
2
O
H
2
O
H
2
O
10
-10
10
-9
H2
O
spectrometr
CH4
10
-10
10
-9
H2
O
spectrometr
CH4
10
-10
10
-9
H2
O
spectrometr
CH4
Cycle
0 25 50 75 100
10
-11
Mass
Time (s)
4
0 25 50 75 100
10
-11
Mass
Time (s)
4
0 25 50 75 100
10
-11
Mass
Time (s)
4
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

4x10
-5
rbance
2940 cm-1
1207 cm-1
Al(CH3)3
chemisorption
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 alternately covered by –OH
Surface alternately covered by –OH
surface groups and –CH3 surface groups
H2O exposure
Purge

0.8
1.2
Cycle
(
Å
)
0.4
owth
per
C
0 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
H2O exposure
Purge

0 8
1.2
ycle
(
Å
)
0.4
0.8
wth
per
Cy
0 20 40 60 80
0.0
Grow
H2
O dose (ms)
Cycle
Conditions such that precursors react
through saturative surface reactions:
H2O does not react with –OH
surface groups
H2O exposure
Purge

1.2
1.6
cle
(
Å
)
0.4
0.8
wth
per
Cyc
CVD+ALD ALD
0 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
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)
0 20 40 60 80 100
0.00
Grow
Dose time (ms)
0 1 2 3 4 5
Purge time (s)
0 20 40 60 80
H2
O dose (ms)
0 1 2 3
Purge time (s)
Plasma ALD - Al(CH3)3 & O2 plasma
0.10
0.15
0.20
Cycle
(nm/cycl
Subsaturation
0 20 40 60 80 100
0.00
0.05
Growth
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
(nm/cycle
(a)
0.0
0.1
Growth
rate
3
4
5
6
(b)
per
cycle
cm
-2
)
0
1
2
3
#
Al
atoms
(10
15
c
0 100 200 300 400
0
Substrate temperature (
o
C)
AlOH* + Al(CH3)3 AlOAl(CH3)2* + CH4
( 3)3 ( 3)2 4
AlOH* + CH4
AlCH3* + H2O
Van Hemmen et al., J. Electrochem. Soc. 154, G165 (2007)

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

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
/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 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

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

ALD of doped films, ternary compounds, etc.

ALD of Al-doped ZnO films
Zn(C2H5)2 + H2O ZnO + 2 C2H6
ZnO
ZnO:Al n cycles ZnO + m cycles Al2O3
101
150 ºC
Al2O3 TMA or DMAI + H2O
100
TMA
cm)
2
10-1
sistivity
(
0 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)
0 5 10 15 20 25 30
Al fraction (at.%)

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
/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
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, USA)

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, SnO2,
TiO2, etc.
Blocking layer Encapsulation
Al2O3, ZnO, TiO2
selective layer
Van Delft et al., Semicond. Sci. Technol. 27, 074002 (2012).
q p
available
g y
HfO2, SnO2, TiO2
p
Al2O3

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
www.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 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

Spatial ALD: S2S and R2R
• Sheet-to-sheet (S2S, or wafer-to-wafer)
M i 1
www.levitech.nl
Movie 1
Movie 2
• Roll-to-roll (R2R)
www.solaytec.com
Movie 2
www.lotusat.com www.beneq.com
www.tno.nl
Movie 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 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

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 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)

Title
/Department of Applied Physics

ALD_Kessels.pdf

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to ALD_Kessels.pdf

Similar to ALD_Kessels.pdf (20)

Recently uploaded

Recently uploaded (20)

ALD_Kessels.pdf