new nano-processing tools nac 05 mar 2007...nanofab tools can be tailored for the controllable...

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©Oxford Instruments

Oxford Instruments

New nano-processing tools - extending the capabilities and opportunities in nanofabrication

John W Burgoyne, Chris Hodson & Cigang XuOxford Instruments

NAC Nanotechnology Colloquium05 March 2007



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Oxford Instruments plc• c. 1,300 people worldwide• c. £160m turnover (2005/06)• Listed on the London Stock

Exchange (OXIG)• 10 manufacturing sites in 5

countriesUK (3)USA (4)Finland (1)Denmark (1)PR China (1)

• First technology spin-out from Oxford University (1959)



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Objective

Enabling nanoscience and nanotechnology

“To become the leading provider of new generation tools and systems for the Physical and Bioscience sectors, based on our ability to observe and manipulate matter at the smallest scale.”



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Quality & environmental measurement

NanotoolsBiotools



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Nanotools

• FabricationTools and processes to create micro- & nano-structures

• CharacterisationChemical and elemental analysis

• EnvironmentsHigh magnetic field, low temperature and optical environments for fundamental nanoscience

• Plasma etch & deposition• Atomic layer deposition• Molecular beam epitaxy• Ion beam etch & deposition



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Key markets and applications

Courtesy of OSRAM Opto Semiconductors GmbH

• Semiconductor• Opto-electronics

HB LEDs, VCSELs, blue/violet laser diodes

• Photonics• MEMS• High-quality optical coatings,

mirrors, filters• Nanotechnology

creating structuresCourtesy of Sharp Laboratories Europe



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Nano-processing tools – the motivation

• There are a lot of tools out there – why do we need more/new/better ones?

Repeatability – same thing every timeControllability – what you want, where you wantSelective processes - when you wantDevices & heterostructuresCleanliness and particle control

- Learning from the semiconductor industry



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Nanotube and nanowire growth tools –Nanofab

Dr Cigang XuDevelopment Scientist



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Nanofab tools

• What do we want to deliver to researchers and device developers?

• Core benefits of all our process tools

Proven processesProcess supportRepeatabilityReliabilityFlexibility

• In a system tailored to nanowire and nanotube growth

Small sample up to 8” wafer capabilityLoadlock wafer handling

- Particle control and safetyFlexible temperature

- 700 °C, 1000 °CProcesses



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Materials of interest

• Carbon nanotubesMulti-wall, single wall

• Si nanowires• Ge nanowires• ZnO nanowires• SiC nanowires• III-V materials

GaN, GaAs, InP….



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Materials of interest

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

CSi

GeGaOZnOInNBNAlNSiC

ZnO MOCVDZnSe MOCVDGaP MOCVD

GaAs MOCVDInP MOCVDSiC MOCVD

Wafer Temperature

PECVD / CVD

MOCVD(LIQUID DELIVERY)

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

CSi

GeGaOZnOInNBNAlNSiC

ZnO MOCVDZnSe MOCVDGaP MOCVD

GaAs MOCVDInP MOCVDSiC MOCVD

Wafer Temperature

PECVD / CVD

MOCVD(LIQUID DELIVERY)



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Nanofab tools – delivering our goals

Liquid precursor delivery to enable

MOCVD

800-1000 ˚C heater for high temperature

applications

700 ˚C for low temperature & O2-based processes

Aligned nanotubes with dc bias

NanofabBase PECVD system



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Nanofab tools – delivering our goals

• Nanofab700Flexible nanowire and nanotube growth up to 650 °C

• Nanofab800AgileFlexible non-oxide nanowire and nanotube growth up to 800 °CAgile heating (up to 130 °C/min) and cooling for rapid turnaround

• Both systems featurePlasma catalyst conditioningLiquid precursor option



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Nanofab production of nanostructuresSi/SiO2 substrate (Wafer)

Si/SiO2 substrate (Wafer)Seed layer (Co)

Deposition of metal catalyst

Step 1: Catalyst treatment Nanofab

Step 2: Growth of CNT/NWs

Si/SiO2 substrate (Wafer)



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Application example: growth of carbon nanotubes

Allotropes of carbon



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Single-walled Carbon Nanotubes (SWNTs)

Multi-walled Carbon Nanotubes (MWNTs)

TEM images



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Applications of nanotubes

• Thin film displays (FED) • Hydrogen fuel cells• Interconnects, heat dissipation• Composite materials• Many more…



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Nanotube Chip

Hair



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Seed layer preparation

• Catalyst metal is usually Co, Ni or Fe for CNT• Can be deposited as a thin film• Can be prepared as catalyst particles• Films need to be treated to ensure particle formation prior

to growth



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Seed layer preparation: effect of plasma

H2 thermal reduction H2 plasma treatment

Effect of plasma on 5 nm Co film, 800 °C, 20 min



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Factors studied for controllable growth of CNT

• Many process variables add up to controllable growthtemperatureplasma treatmentcomposition of process gas effect of pressure with RFeffect of RF/LFeffect of LF power leveleffect of pressure with LFeffect of RF/LF combinationeffect of bias



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Effect of plasma treatment

No pretreatment, thermal growth with plasma treatment, then thermal growth Co(Ac)2catalyst, 700 °C, 50C2H2/50NH3, 1T, 100 W



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Typical CNT grown in Nanofab



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Silicon nanowire growth process

• Need Si-source gas (SiH4), catalyst metal (Au, In, Ga)• Temperature needed lower that CNT growth• Investigating use of etch gases to control a-Si deposition

H2 addition to SiH4 gas proving to be effective



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Si nanowire growth

• ~5 nm thick Au/Pd catalyst layer• Nanowires of varying diameter• Grown thermally by catalytic

decomposition of silane (400 °C)



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Selective Si nanowire growth

• Possible to grow nanowires selectively at catalyst sites (in this case Au particles)

• Larger nanoparticles tend to give straighter nanowires

• Possibility of etching native oxide in plasma system to encourage epitaxial growth

• Grown at 400 °C



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Conclusions

• The development of nanotechnology requires controllable growth of nanostructures

Nanofab tools can be tailored for the controllable growth of materials of interest

• Application example of Nanofab tools: controllable growth of carbon nanotubes

Plasma plays an important role in growing carbon nanotubes, withvarious affecting factors such as growth temperature, frequency and gas composition



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Nanometer thin film growth - atomic layer deposition

Chris HodsonALD Applications Specialist



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What is Atomic Layer Deposition (ALD)?

• Self limiting process giving precise thickness control• Typically using two or more liquid halide or organometalic

precursors in vapour form• Conformal coating even in high aspect ratio structures• Very thin films and low deposition rate• Wide variety of materials possible



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Applications of ALD- mainstream semiconductor and traditional

Area Application Associated film types

High-k dielectric

Interconnects

Hard drives

TFEL displays Phosphorescent layer ZnS:Mn, ZnS:xxCaS:xx, SrS:xx

Gate oxides, storage capacitor dielectrics Al2O3, HfO2, HfSiO, HfON

Cu diffusion barriers / adhesion promoters TiN, Ru, TaN, Ta, WN, WCN

Barrier in magnetic tunnel junctions, used in magnetic read heads

Al2O3, HfO2



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Applications of ALD- non-semi and new


Anti-stiction coatings (charge dissipation and hydrophobic coatings)

Al2O3 (Zn doping for charge)

Passivation of silicon Al2O3

Transparent conductive oxide ZnOWear resistant coatings Al2O3

Heat spreader/dissipater AlN

OLEDs Pinhole free passivation layers for OLEDs and polymers

Al2O3, Si3N4

MEMS

Solar cells



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Applications of ALD- non-semi and new


Hard masks Metal hard masks for etching Al

Pressure sensor membranes Al2O3

Metal electrodes Ru, TaNLab on chip Microfluidics Al2O3

Fuel cells SOFC catalyst PtUV Sensors Transparent conductive oxide ZnO

Nano electronics

…and any application that benefits from thin, precisely controlled, pinhole free, conformal films with materials not possible by conventional (PE)CVD.



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What is atomic layer deposition (ALD)?

1)

2)

3) Purge 4) 5) Purge

Al(CH3)3 exposure

Initial surface

H2O exposure

Example:Al2O3 from Al(CH3)3 and

(1) H2O thermal and(2) O2 plasma



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1)

2)

3) Purge 4) 5) Purge

Al(CH3)3 exposure

Initial surface

O2 plasma exposure

O2 plasma

Example:Al2O3 from Al(CH3)3 and

(1) H2O thermal and(2) O2 plasma

What is atomic layer deposition (ALD)?



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Materials possible by ALD

Adapted from source: Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process, Riikka L. Puurunena, Interuniversity Microelectronics Center (IMEC vzw), JOURNAL OF APPLIED PHYSICS 97, 121301 2005



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Why plasma ALD? Key advantages

• Widest choice of precursor chemistry available• Lower temperature processing – O2 plasma instead of H2O and

better quality of film• Higher quality films – better impurity removal• Effective metal chemistry – H2 or N2 plasma• More process control, e.g. stoichiometry• Higher rates• Plasma surface treatment possible• Plasma cleaning of chamber



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Low T Al2O3 deposition & short purge

400 800 1200 1600 200010-6

10-5

10-4

10-3

H2O

Pre

ssur

e (m

bar)

Pump down time (s)

O2

Pump down time after flowing H2O and O2

10-1 mbar H2O/O2 for 20 sreactor temperature = 55 °C

0 50 100 150 2001

10

100

Remote plasma ALD

Pur

ge ti

me

(s)

Substrate (reactor) temperature (oC)

Thermal ALD

Purge time for thermal ALD of Al2O3 (H2O)and remote plasma ALD of Al2O3 (O2)

Langereis et al., Appl. Phys. Lett. 89, 081915 (2006).



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Why remote plasma ALD?

• Better film qualityLower plasma damage1

More radical speciesHigher plasma densitySource isolation possible

- stop deposition of conductive and insulating coatings

- stop coating in thermal ALD mode

1Remote Plasma Atomic Layer Deposition of Hafnium Oxide, Hyeongtag Jeon, AVS 5th International Conference on Atomic Layer Deposition 2005. (makes a damage comparison of remote vs direct plasma)



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FlexAL ALD process tool

To turbo and pumping

Precursorand purge injection

Ports forin-situ ellipsometery

Plasma gasinjectionRemote ICP

source

Plasma source isolation valve

400°C or 650°Csubstrate heater

Rapid automatic pressure controller



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Example material – Al2O3

TRI METHYL ALUMINIUM

• Precursors:TMA, O2 plasma, H2O

• ApplicationsMedium k (~9) dielectricWear resistant coating of MEMS structuresPassivation layer – good moisture barrier – e.g. OLED passivation



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Al2O3 thickness saturation

• Growth rate 1.18 Å/cycle @ 200 °C• Set TMA dosage time at 20 ms

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.50.00

0.02

0.04

0.06

0.08

0.10

0.12

grow

th ra

te [n

m/c

ycle

]

plasma time [s] 20 30 40 50 60 700.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

grow

th ra

te [Å

/cyc

le]

TMA dosing time [ms]



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Al2O3 linear growth regime

0 100 200 300 400 500 600 7000

20

40

60

80

100

120 25° 100 °C 200 °C 300 °C

thic

knes

s [n

m]

cycle

• Measured by in-situ spectroscopic ellipsometry

Possible to measure layer growth as run progressesGrowth rate 1.18 Å/cycle @ 200 °C

• Linear self limiting growth with number of cycles – classic ALD behaviour

• Note RT (25 °C) growth possiblePlastic/organic compatible



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Al2O3 dielectric for high-density trench capacitors

80 nm remote plasma ALD Al2O3 film in 2.5 µm wide trenches with aspect ratio ~10 deposited in the FlexAL reactorCourtesy of Eindhoven University of Technology & Philips Research.



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Moisture permeation barriers

Encapsulation of polymeric devices to prevent lifetime degradation by water uptake

Flexible OLEDs

Photo Voltaics

Demands on barrier

properties

Excellent barriers demanded for flexible OLEDs

(Lifetime ≥ 10 years)

Polymers

Water vapor transmission rate, WVTR (g·m-2·day-1)10-7 10-5 10-3 10-1

Electro-Chromic

s

Food packagin

g

10 100

WVTR = Water Vapor Transmission Rate



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Moisture barrier results

0.00

0.05

0.10

0.4

0.5

PE-C

VD 1

00 n

m S

i 3N4

Rem

ote

plas

ma

ALD

20

nm A

l 2O3

WVT

R (g

⋅m-2⋅d

ay-1)

PEN

PE-C

VD

100

nm

Al 2O

3

PE-C

VD

100

nm

SiO

2

• Remote plasma ALD: Al2O3 barrier deposition at room temperature

• Excellent single layer barrier (20 nm Al2O3) – WVTR = 5.0·10-3 g·m-2·day-1

• Flexible OLEDs: Thin multilayer barrier stack required to obtain WVTR < 10-5 g·m-2·day-1

• Remote plasma ALD: possibility of SiNx/Al2O3 stack by ALD



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HfO2

0 5 10 15 20 25 300

2

4

6

8

10

12

14

EO

T (n

m)

HfO2 thickness (nm)

• Precursors:TEMAH, O2 plasma, H2O

• ApplicationsHigh k (~18) dielectricGate dielectric



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TiNConformal 40 nm TiN

layer in trench with increasing aspect

ratio

• Precursors:TiCl4, N2/H2 plasma

• ApplicationsConductive nitrideBarrier layer, e.g. Cu diffusion barrierMetal electrode



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TiO2

0 20 40 60 80 100

300°C 200°C

Anatase spectrum

Inte

nsity

Angle [2 Theta]

• Precursors:Ti(OC3H7)4, O2 plasma

• XRD analysis shows phase control

Amorphous @ 200°CAnatase @ 300°CBroad peak is the Si crystal



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Ru

0 10 20 30 40 50 60 700

20

40

60

80

100

Ato

mic

con

cent

ratio

n (a

t.%)

Sputter time (min.)

C O Ti N Si Ru

Oxford - 25 sample

Sputter rate : 10Å/min. Interval : 1.0

In Ru film => Ru : ~98 at.%, O : ~1at.%, C : ~1at.%

In TiN film => O : ~8 at.%, C : ~4 at.%

• Precursors:Ru(EtCp)2, O2 or N2/H2plasma

• ApplicationsBarrier layer, e.g Cu diffusion barrierMetal electrode



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Conclusions

• Proven capability in plasma and thermal ALD processing, including TiN, HfO2, Al2O3, Ru, etc.

• Demonstrated advantages of plasma ALD

• Excellent controlled conformal growth

• Opportunity for highly-controlled nanometer thin films



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Nano-etching for top-down Si nanofeatures

Dr John W BurgoyneNew Business Innovation Manager



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“Traditional” Si etch process chemistry

• Widely used in MEMS structuresAccelerometers, pressure sensors, gyroscopes – many in automotive applications (airbags, tyre pressure, …)

• “Traditional” Si etch process chemistry

Reactive ion etching (RIE)Deep reactive ion etching (DRIE) – “Bosch” process



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DRIE/Bosch limitation – sidewall roughness

• High rateTraded-off vs. feature control

• High aspect ratios• Limitations

Bosch process uses a sequential etch & deposition (passivation) process which limits sidewall smoothness and nano-featured structures

Non-optimised process sequence

“Optimised”process sequence

< 150 nm roughness



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Si nano-feature etching

• Alternative process chemistriesCryogenic SF6 – O2 etchMixed SF6 – C4F8 processHBr process



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Nanoscale Si etching: cryo processing

Photonic crystal – 180 nm holes etched to 1.65 µm depth

Grating structure – 100 nm features etched to 1 µm depth (10:1 AR)



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Nanoscale Si etching: C4F8-SF6 mixed process

50 x 300 nm trenches

16 nm features in Si



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Nanoscale Si etching: HBr based process

34 nm polySi gate etch12 nm gate structure, stopping on 3 nm SiO2. Courtesy of AMO, Aachen



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Summary

• Oxford Instruments is enhancing the nanotechnology armoury with a range of new tools and processes to enable

Bottom-up growth of nanomaterialsTop-down engineering of nanostructuresOverlay and functionalisation with nanometer thin films

• Controllability, repeatability and selectivity are key in nano-processing tools delivering the ability to engineer nano-scale devices



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Thank you to the NAC for this opportunity, thank you for attending.

Further information, please contact:[email protected]

www.oxford-instruments.com

new nano-processing tools nac 05 mar 2007...nanofab tools can be tailored for the controllable...

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