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

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100

120

140

160

180

200

TMA dose [mol] 3.6 0.43 0.33 0.30 0.28

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Position across wafer [cm]

0 2 4 6 8 100

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60

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120

140

160

180

200

TMA dose [mol] 3.6 0.43 0.33 0.30 0.28 0.26

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Position across wafer [cm]

0 2 4 6 8 100

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TMA dose [mol] 3.6

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0 2 4 6 8 100

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TMA dose [mol] 3.6 0.43

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0 2 4 6 8 100

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100

120

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160

180

200

TMA dose [mol] 3.6 0.43 0.33

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0 2 4 6 8 100

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TMA dose [mol] 3.6 0.43 0.33 0.30

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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

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9/6/2007, graph 2

H2O dose [mol]

2.65 1.25 0.81 0.68 0.54

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Position across wafer [cm]

0 2 4 6 8 10-20

0

20

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240

9/6/2007, graph 2

H2O dose [mol]

2.65

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Position across wafer [cm]

0 2 4 6 8 10-20

0

20

40

60

80

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9/6/2007, graph 2

H2O dose [mol]

2.65 1.25

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Position across wafer [cm]

0 2 4 6 8 10-20

0

20

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9/6/2007, graph 2

H2O dose [mol]

2.65 1.25 0.81

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Position across wafer [cm]

0 2 4 6 8 10-20

0

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9/6/2007, graph 2

H2O dose [mol]

2.65 1.25 0.81 0.68

Th

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[A

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Position across wafer [cm]

0 2 4 6 8 10-20

0

20

40

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9/6/2007, graph 2

H2O dose [mol]

2.65 1.25 0.81 0.68 0.54 0.30

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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