Miniaturized non-thermal atmospheric pressure plasma jet ...bonitz/si10/foest.pdf · Miniaturized non-thermal atmospheric pressure plasma jet ... an atmospheric-pressure plasma jet,

Miniaturizednon-thermal atmospheric pressure plasma jet and thin film deposition

R. FoestLeibniz Institute for Plasma Science and Technology e.V. Greifswald

Felix-Hausdorff-Str. 2,17489 Greifswald, GermanyPhone: +49 - 3834 - 554 300Fax: +49 - 3834 - 554 301E-mail: foest@inp-greifswald.deWeb: www.inp-greifswald.de

2nd Graduate Summer InstituteComplex PlasmasAugust 5-13, 2010 Greifswald

2

Foest, Summer School Complex Plasmas 2010

Motivation

Micro plasmasnon-equilibrium plasmas, spatially confined to dimensions of 1 mm or lessgeneration of stable discharges at atmospheric pressure

Fascination for p lasma physics (basics) and technology (application):breakdown of 'pd scaling'high current and energy densities , electron densities as high as 5x1016 cm-3 (e.g. microcavity plasmas)emphasis of boundary-dominated phenomenaUV emission by broadband continuathree body collisions (charge carriers, radical generation ) effective gas heating and momentum transfer from the electric field to the gas molecules, gas dynamics

Advantages of plasma jets with regard to surface tr eatment:Flexible dimensions (several cm … sub-mm), local treatmentAccess to inner walls of wells, trenches or cavities .

J. G. Eden et al.,University of Illinois

20 mm

trench width: 0.12 mm

3


Handheld device based on a capillary plasmajet at atmospheric pressure

4


Outline

• Motivation

Peculiarities of micro plasmas

• Introduction

Principles, Designs and Devices

• Discharge Regimes

Stochastic Mode / Locked Mode

Range of Existence

Experimental characterization

Impact on SiOx deposition

• Conclusion

• Outlook

5


Introduction - Principles

Koinuma (1992): 'microbeam plasma generator'(rf cold plasma jet)

H. Koinuma, H. Ohkubo et al., Appl. Phys. Lett. 60 (1992) 816

Selwyn (1998): Atmospheric Pressure plasma Jet (APPJ ) 13.56 MHz, He/O2, no dielectric between electrodes – for thin film deposition from TEOS

S.E.Babayan, J.Y. Jeong, V. J. Tu, G.S. Selwyn, R. F. Hicks, Deposition of silicon dioxide films with an atmospheric-pressure plasma jet, Plasma Sources Sci. Technol. 7 (1998) 286-288

Tool for deposition of a-C:H films

J. Benedikt, K. Focke, A. Yanguas-Gil, A. v. Keudell, Atmospheric pressure microplasma jet as depositing tool, Appl. Phys. Lett. 98, 251 504 (2006)

6


Main distinctive criteria: Power density (temperature load), operating voltages (E field), Frequency, Geometry, Gas mixtures

Openair Plasma(Plasmatreat)

Atomflo D(SurfX)

Blaster(Tigres)

Plasmabrush(Reinhausen Plasma)

Spottec, Plasma Nozzle(Tantec)

Arcospot(Arcotec)

Introduction - Devices

7


RF

Matchingnetwork

G1 G2 G1+P

OES

Detail of capillary…

active dischargeregion

effluent

Experimental – Plasma Source

8


Source geometry, parameters

DimensionsOuter capillary: di = 4 mm, da = 6 mm, Inner capillary: di = 100 µm to 1 mm

da =1 to 2 mmadjustable relative to nozzle (z)

ConfigurationOuter ring electrodes (Cu):

upper: RF lower: grounded

Mounted on x-y plotter:dynamic deposition, v= 1 cm/s

Analysis of local deposition profile (foot print)

z

ParametersFrequency: 27.12 MHzGases: Ar, O2, HMDSO (‰ range)RF power: 2-40 WGas flow: max. 2 slm (inner capillary)

max. 20 slm (outer capillary)HMDSO: 1 g/h

9


Challenges for thin film deposition (PE CVD) withAPPJ

A Conformal coating of 3D objectssmooth covering of edges

B Adjustable film propertiessolid film without pores and with excellent adhesion

for thicknesses of 50..500 nm(e.g. as permeation barrier,

corrosion protection,

top coat)for thicknesses up to 3 µm (scratch resistance)

Si-Micro systems

Si3N4/Resist/Si Lift-off Structure

10


Film morphology

200 µm

2 µm

11


Thin film deposition using silicon organic precursors

Starting substance: Hexamethyldisiloxane HMDSO (CH3)3-Si-O-Si-(CH3)3

Active plasma volume: Activation, thin film precursor formation (e.g. bydissociation, dissociative ionization)

Transport of activated species to surfaceThin film formation (plasma polymerization)

Influencing film properties:A) Energy per moleculeB) Addition of reactive gas:e.g. oxygen:Reduction of C-content in the film,

‚organic‘ → ‚inorganic‘ characterplasma polymer films → quartz-like SiOx films

+ ��

e-

metastablesexcited particles

(CH3)3SiOSi(CH3)2(+)

+CH3

(+)

+ (2 e-, Ar)

(CH3)3SiOSi(CH3)3

1 µm

SEM micrographof film edge

12


-20 -15 -10 -5 0 5 10 15 200

20

40

60

80

100

[%]

r [mm]

N Si O C Br K

108 106 104 102 100 98400

500

600

700

800

900

1000

binding energy / eV

Cps Si(-O)4 Si(-O)

Si(-O)2Si(-O)3

108 106 104 102 100 98400

600

800

1000

1200

Si(-O)4

Si(-O)

Si(-O)2Si(-O)3

Cps

binding energy / eV

mm

-5 0 5

-20mm 0 mm 20mm

Si 2p-peak:

108 106 104 102 100 980

1000

2000

3000

binding energy / eV

Si(-O)4

Si(-O)3

Si(-O)2Si(-O)

Foot print

Si(-O)4, Si(-O)3 – represent “SiO2” – like anorganic film – center Si(-O)2, Si(-O) – represent plasma polymer like film, increasing org. character - edge

Local Deposition ProfileScanning XPS (Elemental composition)

13


Presence of stochastic filaments

1 cm

2 ms exposure

Observation: short time discharge phenomena

14


Regular filaments in rf capillary discharge –Locked Mode

Exposure: 70 ms 10 ms 2 ms

New mode, different from known stochastic filamentary mode:Locked Mode = regularily patterned, equidistant filaments with

fixed spatiotemporal relation and periodic motionConsequence: Homogenized discharge volume

15


Ordered filaments

Exposure time:0.25 s …. 1 ms

D=15mm, low pressure (Ar, few mbar)

16


Locked Mode

17


Other Observations of Self-organization (DBD)

Anode spots, DBD, Helium (2004)

K. H. Schoenbach, M. Moselhy, W. Shi, Plasma Sources Sci. Technol. 13 (2004), 177.

18


Suggestion: Movement driven by convective electrical current, due to translation of surface charge domains?

Other Observations of Self-organization (Water surface)

A. Wilson, D. Staack, T. Farouk, A. Gutsol, A. Fridman, B. Farouk, Plasma Sources Sci. Technol. 17 (2008), 045001.

19


0 50 100 150

5

10

15

P [W

]Flow [sccm]

Electrode distance 7 mm5

4

3

2

1

3 7 12

Gas flow

P/W

Applied RF Power

Number of Filaments

Ar–Flow

Correlation with power

Electrode distance

Dependence on

distance

h1

h2

n1=3_ n2=4

Locked Mode – mode transitions

Q

APP += 0

mm 20)1( 2111 ≈+= hnhn

222

RF

RF

ϕrhn

hn

+Λ=

⇒Ν∉Λ=

Conditions:

20 - 140 sccm Ar

5 - 16 W, 27 MHz

4 Filaments

Electrode width: 5 mm

Electrode distance: 3 – 8 mm

1..5 filaments

Empirical relations:

20


Systematics - Locked Mode

Nr. 1 2 3 4

S mode

L mode

21


Range of Existence - Locked Mode

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1 2 3 4 5 6 7 8 9 10 11

LM4

LM3

LM2

Locked modes (LM1-4) stationary mode (S4) stationary mode (SM3) stationary mode (SM2) stationary mode (SM1) empirical models (SM1-4) empirical models (LM2-4, eq. 1)

flow

rat

e [s

lm]

RF power [W]

LM1

22


40

45

50

55

60

65

70

75

80

85

90

RF power @ 27.12 MHz [W]

v rot [

cm/s

]

LM 3 Ar 200 sccm (26.7 cm/s) Ar 250 sccm (33.3 cm/s) Ar 300 sccm (40.0 cm/s)

f [H

z]

20

25

30

35

5 6 7 8 9 10 11 12 13 14 15 16 17 18

0 50 100 1500

200400600

Ar 200 sccm, RF 6 W

a k [co

unts

]

fk [Hz]

LM3: Low frequency analysis

FFT, time sequence of 3800 optical emission spectra,

sampling frequency 300 Hzphoto-diode array (TranSpec 2000)

23


13,1 13,2 13,3 13,4 13,528

29

30

31

650 700 750 8000

2000

4000

6000

ln(I

ijλA

-1 ijg i-1

) [

]

Εi [eV]

dy/dx=1/(kBT

e)

Ar I (772.3 nm)4p-4s

Ar I (750.4 nm)4p-4sAr I (696.5 nm)

4p-4s

I ij [

coun

ts]

λ [nm]

Ar I (667.7 nm)4p-4s

LM3: Detail Ar spectrum

Boltzmann method: approximation of the excitation temperatureNo exact real state of excitation equilibrium

Estimation of ‘Effective excitation temperature ’ as a thermodynamic plasma parameter reflecting the relative changes

Applicability of Boltzmann Method:

ne:1012 .. 1013 cm−3

Transition phase between LTE and

coronal phase:

Local partial excitation

saturation phase

24


5 6 7 8 9 10 11 12 13 14 151600

1700

1800

1900

2000

2100

Ar flow 250 sccm

Te [

K]

RF power [W]

5 6 7 8 9 10 11 12 13 14 15200

250

300

350 Te [K]

16001700180019002000210022002300

RF power [W]

Ar

flow

rat

e [s

ccm

]

LM 3

85 Hz

78 Hz

45 Hz

LM3: Excitation Temperature

Effective excitation temperature Texc : - Correlates with operating characteristics of LM3- Increasing function of RF power

Regions of constant Texc : constant frequency f. Increasing f of LM3 : increase Texc. (also for other modes LMn)

Tex

c[K

]

Texc [K]

25


Neutral gas temperature

� Measurement of the rotational states of OH provides approximation of gas temperature within micro channel

� Complementary temperature measurements in the gas flow (fluoroptic fibre probe and IR camera) validate the assumption of a local equilibrium between gas and surface of inner capillary

� Results:� Axial profile of gas

temperature� Decreasing Tg with

increasing flow rate

26


Electron concentration

� Line Broadening of Balmer Hβ and Hγ� Gaussian profile: Instrumental broadening, Doppler broadening� Lorentzian profile: van der Waals broadening, electron imact

broadening (Stark broadening)

Broadened profiles of Balmer Hβ and Hγ. The intensitiesof the Gaussian and Lorentzian profilesare not calibrated.

27


Crossing point method

Determination of electron concentration for given electron temperature.Application of GKS model and crossing point methodEstimation of electron concentration using the GC model applied on the measuredBalmer Hβ (J. Schäfer, et al, Eur. Phys. J. D 2010)

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Locked Mode

Discharge ignition:• Temperature gradients in the gas at the capillary surface, changed boundary conditions, • Development of a different flow profile, still stationary solution for SMn• Consumption of electrical power digitized (number of filaments)• Spending of excess energy, before additional discharge filament is evoked: achieved by

expansion of the ionization volume• Filaments become unstable, length increases, twisting and moving ends along the capillary• Response on the flow profile: Conservation of laminar flow, but with helical flow component

(laminar flow in tubes)• Vice versa, helical flow : stable solution for convective electric current trajectories• Filaments adopt the similar form - lock to helical flow regime.

Relation between axial gas velocity and radial velo city of the rotating filaments?

Observations

Discharges evolve strictly along the tube wall, prominent role of surface effects

29


20 25 30 35 40

20

25

30

35

40

16 Wv ro

t [cm

/s]

vz [cm/s]

LM3 6 W 7 W 8 W

LM3: Correlation of axial gas velocity and radial filament velocity

Higher RF powers: radial velocity exceeds the average axial velocity of the gasIndication for a possible response of the discharge on the acceleration of the gas flow

30


SiOx film with Locked Mode

-4

-3

-2

-1

0

1

2

3

0,2 0,3 0,4 0,5

-4

-3

-2

-1

0

1

2

3

0 20 40 60 80 100

binding %

Pos

ition

[mm

]

Si/O ratio

OO-Si-O O

O-Si-O O

108 106 104 102 100 98

0

500

1000

1500

2000

108 106 104 102 100 980

500100015002000250030003500

108 106 104 102 100 98

0500

10001500200025003000

Si(-O)4

Si(-O)

Si(-O)2

Si(-O)3

Cps

binding energy [eV]

Cps

Si(-O)4

Si(-O)3

Si(-O)2

Si(-O)

Cps

Si(-O)4

Si(-O)

Si(-O)2

Si(-O)3

Analysis Si 2p peak (Scanning XPS)

Lateral dependence of chemical Composition

C – free SiOx films:J. Schäfer, R. Foest, A. Quade, A. Ohl, K.-D. Weltmann, Eur. Phys. J. D 54 (2009), 211-217

31


Fluid model of single filament

RF-excited plasma jet withrotating filamants

Model of fluid dynamics with preassumedplasma generation

approach 1

Model of plasma generation

Filament 1D Filament 2D with gas flow

approach 2

Fil. 3D

gas flowProduction and

transport of active speciesreactions at target surfaces

(deposition)

particle densities and fluxeselectric field, outer circuit

impact of gas flow

32


Conclusion

• Locked mode - distinctive discharge regime of the RF APPJ with applicative potential for homogeneous and symmetric thin film deposition

• Systematic investigation of range of existence / operating conditions of the different locked modes depending on the number of filaments in the active zone

• Examination of LM 3 in Ar:

1. appearance of locked mode associated with increase of effective excitation temperature

2. positive correlation with rotation frequency of the discharge filaments3. (maximum: 35 cm/s, for gas flow velocity of 33 cm/s and RF power of

10 W)4. Determination of effective excitation temperature, rotational

temperature and electron concentration

• Supposition:1. Locked mode can be caused by coupling of the helical gas flow regime

and twisted filament propagation in the jet capillary.2. Establishment of the helical flow regime due to laminar conditions in

the capillary and due to symmetric disturbance of the boundary conditions of the gas flow at the wall with the moving filaments.

33


Acknowledgement

Contributions:

J. SchäferH. LangeA. QuadeS. PetersF. SigenegerM. BeckerC. WilkeK.D. Weltmann

34


Contact

Leibniz Institute for Plasma Science and Technology e.V.Address: Felix-Hausdorff-Str. 2, 17489 Greifswald Tel: +49 - 3834 - 554 300, Fax: +49 - 3834 - 554 301E-Mail: welcome@inp-greifswald.de, Web: www.inp-greifswald.de

Miniaturized non-thermal atmospheric pressure plasma jet ...bonitz/si10/foest.pdf · Miniaturized non-thermal atmospheric pressure plasma jet ... an atmospheric-pressure plasma jet,

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