ultraviolet deposition of thin films and nanostructures boyd - etc brunel... · cv d 1) pl asma -...

Ultraviolet Deposition of Thin Films and

Nanostructures

Ian W. Boyd

ETC

Brunel University

Kingston Lane

Uxbridge

Middx UB8 3PH

UK

T: +44 (0)1895 267419 W: etcbrunel.co.uk E: [email protected]

Outline of Talk

1. Principles & properties of UV Excimer Lamps

2. Development of UV deposition system

3. Potential Applications:

Surface engineering

Oxide, metal deposition

Interface engineering

Nanoparticle deposition & doping

Excimer Excitation Schematic: Rare Gas (Rg)

Xe atoms excited by energetic es to

higher electronic states & even ionised

Excimer (Excited Dimer) molecules

formed by collision

Excimer relaxes by collisions and

photon emission to ground state

Ground state:

Dissociation to original atoms

Non-absorbing to the light produced

Atoms are “Renewable”

Non-polluting chemistry

continuum

Exciplex Excitation Schematic: Rare Gas Halide (RgX*)

High energy electron

excitation & ionisation

3-body recombination

or harpooning reaction

Exciplexes unstable

(ns lifetime) & emit UV

or quench (low P)

or trimer formation

(high P)

B1/2

X1/2

Summary of “Excimer” UV Sources

Excimer (nm) E (eV) UV range NeF* 108 11.48 Ar2* 126 9.84 Kr2* 146 8.49 VUV F2* 158 7.85 ArBr* 165 7.52 Xe2* 172 7.21 ArCl* 175 7.08 KrI* 190 6.49 ArF* 193 6.42 KrBr* 207 5.99 KrCl* 222 5.58 KrF* 248 5.01 XeI* 253 4.91 UV-C

Cl2* 259 4.79

XeBr* 283 4.41

Br2* 289 4.29 UV-B XeCl* 308 4.03 I2* 342 3.63 XeF* 351 3.53 UV-A



Cl2* 259 4.79

XeBr* 283 4.41


Common

Excimer

Lasers



Cl2* 259 4.79

XeBr* 283 4.41


Common

Excimer

Lasers

V E R Y

Expensive !

Classical v. Dielectric Barrier Discharges

Classical v. Dielectric Barrier Discharges

V E R Y Cheap !

Cylindrical Excimer UV Source

Efficiency & Long term stability: 222nm

Excimer lamp: Characteristic features

o Incoherent, almost monochromatic, more than 20 wavelengths,

high UV and VUV intensities

o Robust and inexpensive, ecologically beneficial (Hg free)

o Long stable lifetime

o No self-absorption, high efficiency

o Easy to handle, no major cooling

o Scalable - large areas possible (cm2-m2)……..

Bond Dissociation Energy of Covalent Bonds

and Wavelengths of Excimer UV Radiation



….lots of available photochemistry !

Outline of Talk




Surface engineering




Lamp Chamber Reactor Chamber

Large area excimer lamp system

Uniformity modelling of three lamp system

UV intensity profile of three lamp system

Distance (cm)

0

50

100

150

200

250

300

7 6 5 4 3 2 1 0

0

50

100

150

200

250

300

7654321

8 cm from lamps

UV

in

ten

sity

(W

/m

)2

edge of left lamp edge of right lampcenter of middle lamp

Extent of 100 mm wafer

Outline of Talk




Surface engineering




Treatment of Polymer Surfaces

Low

High

Fluence

UV irradiation

c leaning

Polymerisation, cross-linking Oxidation, bond/chain breaking

Surface modification, roughening

Removal by laser ablation or photoetching

Hole drilling

Polymer

VUV Surface Modification of Polymide: 126nm

Non-irradiated

20 seconds

60 seconds

120 seconds, 126 nm lamp

100nm

No-irradiation

120 seconds, 126 nm lamp

XPS results show photo-dissociation

of imide groups in Polyimide during

126 nm VUV irradiation

Surface changes of PET irradiated for different times with a 222nm excimer lamp

UV Surface modification of PET

Surface changes of PET irradiated for different times with a 222nm excimer lamp

UV Surface modification of PET

……….can be used to promote surface adhesion

Patterned Treatment of Polymer Surfaces

Copper structures on aluminium nitride

5 µm

Photo-oxidation of Silicon: Si +h + O2



O2

Emission spectrum of the second excimer continua of

Ar2* rare gas dimer

Wavelength (nm)

FTIR spectra of SiO2 grown by 126nm excimer lamp at room temperature

Growth of SiO2 with 126 nm excimer radiation:

10

15

Th

ickn

ess (

nm

)

Growth of SiO2 with 126 nm excimer radiation:

Room Temperature !

10

15

Th

ickn

ess (

nm

)

126nm Oxidation: Summary

Successful room temperature oxidation of Si using 126nm radiation

XPS and FTIR confirm high quality and stoichiometric SiO2 formed.

Leakage current densities as low as 5 x10-8 A/cm2 at an applied

electric field of 1 MV/cm.

Significant oxidation rates, as high as 8 nm/min achieved.

Thicknesses up to 24 nm readily obtained with no growth saturation.

Rapid oxidation related to creation of aggressive O1S oxidant.

Photo-oxidation of Silicon-Germanium

High-resolution XTEM image of UV Oxidised SiGe

Outline of Talk




Surface engineering




Photo DEPOSITION of Dielectrics

Photo-CVD Apparatus

UV Lamp

Chamber

Processing

Chamber

To pumps

UV

Shower

head

Precursors

Wafer

Sample heater

SiH4, O2,

N2O, NH3

Deposition of Si oxide, oxynitride, and nitride using

SiH4 with various N2O/NH3 precursor ratios

Wavenumber (cm-1)

Metal Oxide Deposition:

Photo-CVD reactor incorporating bubbler/digital liquid

injection & “designer” precursors

“Designer”

Precursor

Excimer lamp deposition of metal oxides

using UV-Injection Liquid Source (UVILS):

TiO2

Ta2O5

HfO2

Tantalum Precursor

• Ta (OEt)4 (O CH2 CH2 N Me2) Et : CH3 - CH2

Me: CH3

EtO

EtO

EtO

EtO Ta

O

CH2

CH2

N

Me Me

Tetra ethoxy (dimethyl amino ethoxy) tantalum

Precursor Injector

UVILS-CVD: Ta2O5

0

10

20

30

40

50

60

To

x (

nm

)

0 50 100 150 200

Number of drops

Thickness (nm) 2.5 Å / injection

Uniformity of UV processed Ta2O5 films

800

850

900

950

1000

1050T

hic

kn

ess

(Å

)

Refr

act

ive i

nd

ex

1100

2

2.04

2.08

2.12

2.16

2.2

0 2 4 6 8 10

Thickness: <1.7%

Refractive index: 2.09±0.004 (<0.43%)

Distance across a 4 inch wafer (cm)

Growth rate of photo- and thermal- CVD of

Ta2O5 films

0

1

2

3

4

5

6

7ln

R (

nm

/min

)

1.2 1.4 1.6 1.8 2 2.2

1/T (1000/K)

Photo-CVD

Thermal-CVD

Fig.2

Ea=1.97 eV E

a=0.078 eV

200°C300°C400°C500°C

FTIR spectra for for Ta2O5 films deposited by

photo-CVD at 350°C and UV annealed at 400°C

Tra

nsm

itta

nce

(a

.u.)

2200 1800 1400 1000 600

Wavenumber (cm-1)

as-deposited

0.5h annealing

1.0h annealing

Ta-O

suboxides

Si-O10%

The SiO2 interface layer: UV Annealing

As deposited 15 mins 25 mins 40 mins

The SiO2 interface layer: UV Annealing

As deposited 15 mins 25 mins 40 mins

…….can the interfacial oxide be reduced ?

Outline of Talk




Surface engineering




Suppression of interface oxide by Pre-

deposition UV-anneal in N2O

Demonstrated previously, BUT typically T > 800oC

Pre photo-CVD at 350oC

0 minutes 10 minutes 20 minutes

Comparison of leakage current densities

in Ta2O5 films obtained by different methods

CVD1) Plasma - CVD2) Photo - CVD (our work) 3)

as-deposited

annealing as-deposited

annealing as-deposited

annealing

Leakagecurrent

density at1 MV/cm(A/cm2)

10-3 10-8 10-3 10-6 2.19x10-5 1.5x10-8

Depositedor annealed

temp350°C 800°C 500°C 700°C 350°C 400°C

• Snapshot overview of UV excimer lamp technology

• Example applications towards low temperature deposition

of high quality electronic films demonstrated

Rapid photo-oxidation

Photo-deposition of dielectrics

Metallization & nanocrystalline formation

Surface modification & patterning

NC-embedded matrices

• Applications in many other areas

Surface modification, crystallisation

Packaging

Pollution control & Water treatment

Curing of Paints, Varnishes, Coatings,

Dry lithography, Printing

Biological/Medical…..

Summary

Thank you for your attention !

ultraviolet deposition of thin films and nanostructures boyd - etc brunel... · cv d 1) pl asma -...

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