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Spatial Atomic Layer Deposition: ASpatial Atomic Layer Deposition: A Path to High-Quality Films on
C ti S b t tContinuous Substrates
David H. Levy, Roger S. Kerr, Shelby F. Nelson, Lee W. Tutt, and Mitchell Burberry
Eastman Kodak CompanyRochester, NY
Agenda
Atomic Layer Deposition (ALD) as a processSpatial ALDSpatial ALD• Approach• Performance
Devices and patterning using Spatial ALD• Working demonstrations of film quality• Effective film patterning with ALD
Atomic Layer Depositions (ALD)ALD: process where a substrate is exposed to reactive gases one by one
Film growth occurs
s re
peat
ed
Film growth occurs layer by layerPrecursor (I)
Cyc
le is
High quality
ConformalPrecursor (II) Conformal
Low temperature
© Eastman Kodak Company 3
Atomic Layer Deposition Uses
Barrier layers• Very conformal and dense coatingVery conformal and dense coating• Prevent moisture and oxygen transmission• Thin layers (100–200 Å) are effective
Thin, high-performance dielectrics• New generation silicon chips: 25 A layers with low electrical
leakageg
Many other applications• Coating of high aspect ratio structures• Transparent conductors• Oxide and other binary/ternary semiconductors
Spatial Atomic Layer Deposition (S-ALD)
ChamberALD
SubstrateExposureALD
Inert (II)(I)Time
Exposure
SpatialALD S-ALD Head
Q
SubstrateExposure(Point Q)
Spatial Process
ALD S ALD HeadTime
p• Steady-state gas flows• Can be “open air”• Suitable for large or continuous substrates
Isolating the Reactive Gases
Gas confinement is keyThere is a variety of proposed y p psystems for gas confinement
Inert (II)(I)Gas
regions
Source andexhaust slots
The ALD Coating Head
PP
Small GapL G
Large gap to substrate
Large Gap
• Low pressure gradients• Gas will mix across many channels
Small gap → Substrate floats (gas bearing)Small gap → Substrate floats (gas bearing)• High pressure to drive from source to exhaust: Good Isolation• Excellent control of substrate position• Very small “chamber”• Very small chamber
Equipment Design
Current work is on aCurrent work is on a laboratory scale unit• 2" wide coating width• Used with discrete 2.5" square
substrates
Process demonstrationsProcess demonstrations• Gas isolation• ALD film growth and saturation• Open air operation →
extendability to long substrates
8
Isolation of Precursor GasesHow good is the gas separation?• Measure by using a “tag” gas (NH3) in the metal channels
P
• Look for crossover of this gas to the oxygen channels
“metal”h t
ppm level NH3 detector
Results
exhaust “oxy-”exhaust
Pure NH3
pp 3
• Stationary operation: No detectable mixing• At our current maximum velocity (0.26 m/s): ~23 ppm mixing• Gas phase reaction minimal factor
© Eastman Kodak Company 9
• Gas phase reaction → minimal factor
Saturation Behavior for TMA/Water
Relative residence times hard wired by h d d ihead designHowever• Constant flow: accurate
1.2
1.4 200 °C
• Constant flow: accurate control over chemistry levels
• Very sharp chemistry changes 0 6
0.8
1.0
h/C
ycle
(Å)
PTMA(mTor)
PWater(mTor)
g
Clear saturation behavior
Å0.2
0.4
0.6
Gro
wth r) r)
300 170
30 170
• Saturation near 1.2 Å/cycle for TMA/Water
0.00 500 1000 1500 2000 2500
Residence Time (msec)
300 17
30 17
© Eastman Kodak Company 10
Equipment Development (underway)
Objectives• Increased coating width• Web handling
d
Phase A• Coating head migration to 6” width
6 in
ch ri
gid • Coating head migration to 6 width
• DEMO: Ability to construct wider heads
• DEMO: Uniform delivery of gas6s
DEMO: Uniform delivery of gas
Phase B
Sho
rt P
ass
Web
• Short pass 6” web unit• DEMO: Ability to handle free
standing webs
S
Throughput
Empirical model can be constructed for a given reaction systemreaction system
1.200
1.400
GPC
(A)
1.200
1.400
GPC
(A)
Cyc
le
Slot spacing gth
0.000
0.200
0.400
0.600
0.800
1.000
G
GPC
GPC-Calc
0.000
0.200
0.400
0.600
0.800
1.000
G
GPC
GPC-Calc
Gro
wth
per
C p g
Rea
ctor
Len
RequiredThickness
Currently have good data on Al O and ZnO
0.000 1.000 2.000 3.000Residence (sec)
0.000 1.000 2.000 3.000Residence (sec)
Residence TimeModel
Web Speed
Currently have good data on Al2O3 and ZnO system
12
Throughput for Al2O3 or ZnO
30
00A
(m)
The material system tt
30
00A
(m)
230 mTorr
15
20
25
Leng
th fo
r 100 matters
Slot spacing is a weaker dependence
15
20
25
Leng
th fo
r 100
Al2O3Water
5 9 Torr
0
5
10
Zone
weaker dependenceLonger spacing• Longer residence →ZnO0
5
10
Zone
L 5.9 TorrWater
00 5 10
Speed (m/min)
• Longer residence → more deposition per cycle
• Easier head assembly
ZnO00 5 10
Speed (m/min)
Gro
wth
Per
Cyc
le • Easier head assemblyTo date: Small to no effects when not in complete saturation
Example:200 Å Film5 m/min web speed
Residence Time saturation → 1.6 m zone
S-ALD ZnO Thin-Film Transistors (TFT)
TFTs: the drive element for flat displays• Laptop screen: a-Si TFTs with mobility ~1 cm2/V-sLaptop screen: a Si TFTs with mobility 1 cm /V s
To drive an OLED• Higher mobility is needed to handle the pixel current
E t d
• Higher stability is needed to continuously supply the pixel
ZnO is a promising alternative
250 Å ZnOBy the SpatialALD Process
EvaporatedAl Contacts
Vd
i
Glass ITO Gate Layer on Glass
1100 Å Al2O3
ALD Process
Vg
© Eastman Kodak Company 14
(commercially obtained)Side View, Schematic
Typical Device Performance
1.E-03
m2) DF141-6-D6C-ID-[VA=0]
DF141 4 D1E ID [VA 0]1E 02 (A)
Al2O3 Dielectric Leakage
1.E-07
1.E-06
1.E-05
1.E-04
eaka
ge (A
/cm DF141-4-D1E-ID-[VA=0]
DF141-2_D2C-ID-[VA=0]
1E-06
1E-05
1E-04
1E-03
1E-02
Dra
in C
urre
nt
150 °C200 °C
W/L = 600/50 mmTox= 1100 ÅITO GateShadow mask Al contacts
1.E-10
1.E-09
1.E-08
0 2 4 6 8 10Applied Field (MV/cm)
Le
1E-11
1E-10
1E-09
1E-08
1E-07 250 °C
High on/off ratio >108
IgApplied Field (MV/cm)
1E-12
1E-11
-10 0 10 20 30Gate Voltage (V)
Additional Characteristics…St bilit C bl t SiHigh on/off ratio 10
Low gate leakage <2.5 × 10-8 A/cm2
Mobility: ~15 cm2/V-s
Stability: Comparable to a-Si.2.3 MHz ring oscillator circuits: Fast (J. Sun, et al., IEEE Electron Device Lett.))
Mapping Electrical Characteristics
Deposited film on Si( h thi k t ) Map of Linear Differential Mobility(shows thickness steps)
Thinner dielectric and
Measurement region: Central area
Thinner dielectric and semiconductor
© Eastman Kodak Company 16
TFTs with Shadow-masked Al Contacts
Linear Mobility Vth12 3 ± 0 6 cm2/V-s 4 68 ± 0 04 V12.3 ± 0.6 cm /V-s 4.68 ± 0.04 V
240 devices
© Eastman Kodak Company 17
Bias Stability
Initial observations• Stability depends on Gate Bias (not current flow)Stability depends on Gate Bias (not current flow)• Mobility shows little change
Conditions• Typically stress time = 10,000 s• Bias applied Vg = 10 V (for gate dielectric thickness = 50 nm)• Relatively high field (2 × 106 V/cm)Relatively high field (2 × 10 V/cm)
For W/L = 500/50• Linear: Vd = 0.25 V, drain current ~50 μA• Saturation: Vd = 10 V, drain current ~0.9 mA
© Eastman Kodak Company 18
Passivated TFTPassivation with alumina in Spatial ALD system
200 °C processThickness = 50 nm
1.0E-06
1.0E-05
1.0E-04
t (A
)
Al
Al2O3
Chromium Gate
ZnOAl
1.0E-09
1.0E-08
1.0E-07
Dra
in C
urre
n
t = 0 s
t = 10000 s
Glass
1.0E-11
1.0E-10
-10 -5 0 5 10Vg (V)
0 80.91.0
ent Low
0.00.10.20.30.40.50.60.70.8
1 10 100 1000 10000 100000
Nor
mal
ized
Cur
re
Low movement of threshold or
current
© Eastman Kodak Company 19
Stress Duration (s)
Patterning and R2R ALD
Typical Semiconductor ProcessingPhotolithographic processPhotolithographic processLayers applied, then patterned with photoresist + etching
Large-area processing: A new landscape
Material Process Printed Patterning
Direct Print Functional Materials
Physical Vapor Deposition
Chemical Vapor Deposition
ALD
?Selective Area
Selective Area Deposition
Reaction inhibition• If precursors cannot react
with the substrate, the film does not grow
Advantages• Thin inhibitor layers
I hibit b i t d• Inhibitors can be printed• After ALD, film is ready for
next layer
Characterization of Growth Inhibition
ess)
½ Sample N I hibit
½ Sample O.D
. (~t
hick
ne
(inhibition)
Inhibitor spun on sample
No Inhibitor InhibitorALD Cycles
During ALD growth, sample removed periodically• No inhibitor: Normal surface growth
I hibit id R d d/ li i t d th• Inhibitor side: Reduced/eliminated growth
Growth of ZnO characterized with 355 nm optical density
PMMA: a Good Inhibitor
PMMA solutions spun on borosilicate glass• 950 000 MW (Microchem 950 PMMA A4)
38 A PMMA
• 950,000 MW (Microchem 950-PMMA-A4)• Thicknesses by ellipsometry on silicon controls (3000 rpm)
– 9 Å (0.025% solution)18 Å (0 05% l ti )
1
1.2
1.418 A PMMA
9 A PMMABare
@ 3
55 n
m
– 18 Å (0.05% solution)– 38 Å (0.1% solution)
Inhibition results
0.4
0.6
0.8
O.D
. @
Inhibition results• Strong inhibition even for
9 Å film40 Å it bl f t
0
0.2
0 500 1000 1500
ALD Cycles
• 40 Å suitable for most applications
• Thinness: Quick inhibitor l f i li ALD Cyclesremoval for inline process
TFT Structure Completely by Selective Area ALD
1000 Å Doped ZnO 1100 Å Al2O3 300 Å Intrinsic ZnO 1000 Å Doped ZnO
StSt St StStampStamp Stamp Stamp
PDMS Based StampingPDMS Based Stamping
Result: Working transistor with mobility ~3 cm2/V-s 1.0E-06
1.0E-05
1.0E-04
1.0E-03
Drain Current (Vd=10V)Drain Current (Vd=20V)Gate Leakage (Vd=10V)Gate Leakage (Vd=20V)
mobility ~3 cm /V-sAll layers by ALDAll patterning by selective area depositionTransparent too! 1.0E-12
1.0E-11
1.0E-10
1.0E-09
1.0E-08
1.0E-07
© Eastman Kodak Company 24
Transparent, too! -10 0 10 20 30
Conclusions
Spatial ALD Approach• Open air performance demonstrated on rigid
substrates
• Scaleup and flexible work underway• Scaleup and flexible work underway
A li iApplications• High performance semiconductor /
dielectricsdielectrics
• Accessible patterning
© Eastman Kodak Company 25