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Spatially Distributed Spatially Distributed Experimentation to Experimentation to
Understand ALD Process Understand ALD Process Chemistry Chemistry
Rubloff Research Group Accomplishments
Rubloff: Spatially distributed atomic layer deposition
Spatially Distributed Atomic Layer Spatially Distributed Atomic Layer Deposition (ALD)Deposition (ALD)
AccomplishmentDesigned and implemented ALD reactor
to achieve spatial distribution of impingement fluxes
Demonstrated spatial gradients in thickness and material properties
SignificanceAtomic layer deposition (ALD) is widely
sought for its atomic-scale thickness control and unprecedented uniformity and conformality
Precursor dose permutations add complexity to ALD process recipes, where underlying surface chemistry is not well understood
Spatially distributed ALD enables rapid investigation of ALD process/dose recipes and optimization of material properties
Researchers involvedLaurent Henn-Lecordier, Gary W. Rubloff
SupportNSF IMI, PAT-IRST MicroCombi, Laboratory for
Physical Sciences, MKS Instruments
Rubloff: Spatially distributed atomic layer deposition
Spatially Distributed Atomic Layer Spatially Distributed Atomic Layer Deposition (ALD)Deposition (ALD)
Intellectual meritAtomic layer deposition (ALD) enables atomic-
level control of ultrathin film deposition over 3-D surfaces. It relies on alternating doses of molecules that saturate surface sites to achieve these benefits.
ALD surface chemistry is not well-understood, so finding suitable dose recipes is hampered by the numerous permutations available.
We have designed and implemented an ALD reactor design that uses cross-flow of precursor gases to achieve combinatorial variation of surface reaction conditions across a 4” wafer.
We have demonstrated the fabrication of spatial gradients in thickness and material properties for an Al2O3 ALD process.
Coupled with rapid characterization of across-wafer material and electrical properties, the cross-flow ALD reactor provides a platform for addressing the relation of ALD process chemical conditions to resulting material properties.
Rubloff: Spatially distributed atomic layer deposition
Spatially Distributed Atomic Layer Spatially Distributed Atomic Layer Deposition (ALD)Deposition (ALD)
Broader ImpactsAtomic layer deposition (ALD)
is widely sought for its atomic-scale thickness control and unprecedented uniformity and conformality, key benefits for existing technologies (e.g. semiconductors) and for a broad set of nanotechnology applications.
The numerous precursor dose permutations inhibits fundamental understanding of ALD surface chemistry and process applications.
Our cross-flow ALD design and associated material characterization provide a platform for rapid learning in ALD process behavior and enhanced development of ALD applications.
Close collaboration with Italy group (FBK-irst) has been essential in chemical, compositional, and structural characterization of ALD layers.
TMA dose
H2O dose
Optimal properties
saturatingdoses
Rubloff: Spatially distributed atomic layer deposition 08/25/05 5
• Alternating doses of chemical precursors, repeated approximately once per atomic layer
• Self-limiting adsorption/reaction for each dose
Growth of 1 monolayerof metal oxide
SUBSTRATE
OH OH OH
M LL
L
L
OH OH O
M LL
L
L
M LL
L
LH
M LL
L
M LL
L
M LL
L
M LL
L
M LMOH
OH OH
H2O
MM
OH OH
O O O
O O OO O O
O O M
OH
Initial surfaceMetal precursor
exposure Purge
Water exposurePurge
O
LH
H2O
H2O
Atomic Layer Deposition (ALD)Atomic Layer Deposition (ALD)
Rubloff: Spatially distributed atomic layer deposition 6L. Henn-Lecordier - 54th AVS TF-Mo M10 - 10/15/07
ALD mini- reactor
Z-axis pneumatic actuator
Moveable cap
MKS RGA
50µm orifice
100 mm wafer
Substrate heater
UHV chamber
0.1 torr
10-5 torr
Gas InletGas Outlet
Cross-Flow ALD ReactorCross-Flow ALD Reactor
Rubloff: Spatially distributed atomic layer deposition
Across-Wafer AlAcross-Wafer Al22OO33 ALD Film Properties ALD Film Properties
0 2 4 6 8 1080
100
120
140
160
180
Position across wafer [cm]
0 2 4 6 8 10
1.20E-010
1.40E-010
1.60E-010
1.80E-010
2.00E-010
2.20E-010
Position across wafer [cm]
0 2 4 6 8 106.8
7.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
Position across wafer [cm]
0 2 4 6 8 101.64
1.66
1.68
1.70
1.72
1.74
Position across wafer [cm]
Thickness (Å) Capacitance (F)
Refractive indexPermittivity
Under-dose H2O conditions (0.8µmol)
Rubloff: Spatially distributed atomic layer deposition 8
0 2 4 6 8 100
20
40
60
80
100
120
140
160
180
200
TMA dose [mol] 3.6 0.43 0.33 0.30 0.28
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 100
20
40
60
80
100
120
140
160
180
200
TMA dose [mol] 3.6 0.43 0.33 0.30 0.28 0.26
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 100
20
40
60
80
100
120
140
160
180
200
TMA dose [mol] 3.6
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 100
20
40
60
80
100
120
140
160
180
200
TMA dose [mol] 3.6 0.43
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 100
20
40
60
80
100
120
140
160
180
200
TMA dose [mol] 3.6 0.43 0.33
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 100
20
40
60
80
100
120
140
160
180
200
TMA dose [mol] 3.6 0.43 0.33 0.30
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
Saturating H2O dose(1.25 μmol)
Moderate under-dosing TMA causes uniformity degradation & depletion
Larger under-dosing TMA condition generates very strong nonuniformity, nearly discontinuous profile
Enhance growth rate at inlet with dramatic depletion at outlet
Possibly OH oversaturation at inlet which getters and reacts the under-dosed TMA
AlAl22OO33 ALD: TMA under-dosing ALD: TMA under-dosing
Rubloff: Spatially distributed atomic layer deposition
9
0 2 4 6 8 10-20
0
20
40
60
80
100
120
140
160
180
200
220
240
9/6/2007, graph 2
H2O dose [mol]
2.65 1.25 0.81 0.68 0.54
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 10-20
0
20
40
60
80
100
120
140
160
180
200
220
240
9/6/2007, graph 2
H2O dose [mol]
2.65
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 10-20
0
20
40
60
80
100
120
140
160
180
200
220
240
9/6/2007, graph 2
H2O dose [mol]
2.65 1.25
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 10-20
0
20
40
60
80
100
120
140
160
180
200
220
240
9/6/2007, graph 2
H2O dose [mol]
2.65 1.25 0.81
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 10-20
0
20
40
60
80
100
120
140
160
180
200
220
240
9/6/2007, graph 2
H2O dose [mol]
2.65 1.25 0.81 0.68
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
0 2 4 6 8 10-20
0
20
40
60
80
100
120
140
160
180
200
220
240
9/6/2007, graph 2
H2O dose [mol]
2.65 1.25 0.81 0.68 0.54 0.30
Th
ickn
ess
[A
ng
stro
m]
Position across wafer [cm]
Under-dosed TMA (0.33 μmol)
1 Å/cycle
H2O/TMA < 2
improved uniformity but mean thickness decreases due to insufficient reactant supply
H2O/TMA > 2
profound nonuniformity at front and rear, with limited uniformity at middle
AlAl22OO33 ALD: H ALD: H22O under-dosingO under-dosing