physical vapour deposition of thin film coatings

1

European Summer School PPST 2008

WITOLD GULBIŃSKI

Institute of Mechatronics, Nanotechnology

and Vacuum Technique

Koszalin University of Technology, PL

Physical Vapour Deposition of Thin Film CoatingsPart II

Magnetron sputtering

2Institute of Mechatronics, Nanotechnologyand Vacuum TechniqueKoszalin University of Technology, PL

Koszalin, August 18-29, 2008


OutlineInteraction of charged particles with electric and magnetic field. Magnetron effect.

Magnetron sputtering sources (coaxial, planar and other constructions).

Unbalanced magnetrons (closed field systems).

Magnetron sputtering sources for magnetic materials.

Pulsed magnetron sputtering (unipolar and bipolar sputtering, suppression of unipolar arcs)

High power magnetron sputtering – selfsputtering.

High Power Impulse Magnetron Sputtering (HIPIMS)




MAGNETRON SPUTTERING SOURCES




Electron motion in homogeneous magnetic field




Drift of electron in inhomogeneous magnetic field.

A

A

A-A




Electron motion in so called

“magnetic mirror" area.

Magnetic „bottle”




Electron motion in crossed, homogeneous

electric (E) and magnetic (B) fields.

cathode

vdRL

ve

vR E B

anode+

-

Let’s add electric field E perpendicullar to magnetic field vector B




Basic configurations of cylindrical magnetron sputtering systems:a) the general one, b) so called post-magnetron configuration with the cathode end-plates,c) multi-trap configuration

_ _ _+ + +




Cylindrical magnetron cross section

a) discharge structure,

b) electron paths.

a)

b)




Advantages of co-axial magnetrons,

Homogeneous target erossion,

High deposition rate (when compared to diode systems)

Very large substrate mounting space

Drawbacks of co-axial magnetrons,

High thermal load to substrates dueto electron bombardment (electroncollecting grid anodes)




Inverted cylindrical magnetron.

N

S S

N

anodecathode




Planar magnetron sputtering sources: rectangular(a) and circular(b)




Electron movement over the planar magnetron cathode.

cathode




Planar magnetron source - secondary electron escape paths




Discharge voltage vs. discharge current for planar magnetron source for different magnetic field magnitude.




Discharge voltage vs. discharge current for planar magnetron source for different argon pressures.

I [A]c

B = 500 Gsgas - Artarget - Tiplanar magnetron

6.5 10 Pa-2

U [V]c

0.11-1 Pa

0.1 Pa0.08 Pa

0.065 Pa




0

0,5

1

1,5

2

2,5

0 5 10 15 20 25 30

Power density [W/cm2]

Dep

ositi

onra

te[ µ

m/m

in]

WTiCr

AlNiPt

CuAuAgSn

1192320C

1089620C

19710640C

6310840C

19517680C

276600C

Argon40

18434220C

4816680C

Dependence of deposition rate of metals on power density at the target (planar magnetron).




Film thickness distribution for different target - substrate distance (magnetron cathode diameter: 80 mm)




Planarmagnetron source –constructiondetails




Sputter gun




Magnetrons with rotated targets Coating of large surfaces

Continous coating of foils




Double source magnetron sputtering system – combination od planar and rotatingtarget sources (deposition of 2-component coatings)




Triple source magnetron sputtering system – for deposition of 3-component CMA coatings

2 inch planar magnetrons (Al, Cu, Fe)

Rotated and heated substrate holder

3xDC power supply in master-slavemode

LN2 trap




Planar magnetron with additionalhot filament

Thermally emited electrons areinjected into the magnetic trap

Enhanced ionization

Lower working pressure




Magnetron sputtering of ferromagnetic materials(Fe, Co, Ni…)

Ferromagnetic target

Short circuit for magnetic field

No magnetic field above the cathode(target)

TARGET SECTIONALIZATION




Advantages of planar magnetron sources

High deposition rate (up to hundreds nm/min)

DC and RF operation possible

Low discharge voltage (200-600V)

Low working pressure (1Pa)

Easy upscaling

Easy maintenance

Easy design of multisource systems

Plasma confined in target vicinity (coating oftemperature sensitive materials possible)




Unbalanced magnetrons– why and what does it mean?

For the balanced magnetic circuit: the intensities of magnetic flux through the pole faces of the outer poles and through the pole face of the inner pole are identical or comparable.

A preferred strengthening or weakening of one of the involved poles of the magnet leads to “unbalanced” magnetic circuit.

Such an effect can be obtained by:

the change of cross section surface ratio of outer and inner pole of the magnet,

external field source




Balanced (a), permanently unbalanced (b) and externally unbalanced (c) magnetic circuits of planar magnetron sputter source.




a) Dual unbalanced magnetron closed - field system called „ionic gemini”

b) Four source, closed field sputtering system

b)

a)

Opposite poles




Advantages of unbalanced magnetrons

Plasma expanded to the substrate,

Higher (up to 10mA/cm2) ion current density at the substrate

Ion assisted deposition possible

„Closed field” multi-source systems widely used by industry for hardand wear resistant coatings deposition




Pulsed magnetron sputtering

Why?

Deposition (direct and reactive) of insulating films means:

arcing problem (unipolar and bipolar arcs)

disappearing anode effect

low deposition rate




What is unipolar arc?

Dielectric island(Al2O3), few nm thick+ + + + + + + + + + +

Metallic target (Al) at high negative potential

PLASMA

Cathode

Electric field higher thanbrakedown field

Local arc discharge




Fundamental capacitor model.

J. Sellers, Surface and Coatings Technology 98 (1998) 1245 - 1250

Plasma

Target A1

Al O (dielectric)2 3

(dielectric)

Plasma

Target

Dielectri c breakdown(Micro - Arcing)




Arrangements for unipolar (a) and symmetric bipolar (b) pulsed magnetron sputtering

a) b)

pulsedpower supply

pulsedpower supply

disappearing anode andarcing problem solved




Normal sputter mode

Asymmetric bipolar pulse sputtering(single source)

T0-T1 duty cycle < break down voltage buildup time




Reversal mode (neutralizationof positive surfacecharge at the dielectric)


+Vrev about 10% of Vsputt.




Return to sputter mode





Magnetron sputter source with double ring plasma on 2 electrically separated targets

Can be operatedin bipolar mode




High power DC magnetron sputtering(self-sputtering of metals)

Due to high power dissipated at the target of „self-sputtering” source, ionisation conditions change resulting in an increased number of ionised target atoms in the plasma.

According to energy exchange model metal ions, carrying the mass equal to that of target material atoms, induce very effective sputtering.

When the power density at the cathode exceeds a „self-sputtering”threshold value, argon supply can be closed and the discharge becomes sustained by metal ions only.

In transition region between classical sputtering and self-sputtering, both these processes coexist.




Light emission spectra recorded during coppersputtering in argon, at three target currents.

Radzimski et al.: J. Vac. Sci. Technol. B, Vol. 15, No. 2, Mar/Apr 1997




New trends:High power impulse magnetron sputtering (HIPIMS)

Very short pulse duty time (few % of AC voltage period)

Very high discharge current in pulse (in kA range)

High fraction of ionized target material in the plasma

Medium deposition rate

Hysteresis effect during reactive sputtering highly suppressed -stable reactive deposition




Peak power density: 2000 Wcm-2

Repetition frequency; 100 Hz (T = 10ms)Current pulse duty time = 200µs i.e. 2% of the pulse periodPlasma density n = 1013 cm-3 (classical magnetron: n = 1010 cm-3)

High Power Impulse Magnetron Sputtering (HIPIMS)A. P. Ehiasarian (2001)




In conventional magnetron discharges:

HIPIMS exhibits n = 1!

nkUI =where: n = 5…10

HIPIMS

Ehiasarian, A.P. R.; Munz, W.-D.; Hultman, L.; Helmersson, U.; Kouznetsov, V., Vacuum, 65 (2002) 147-154




HIPIMS

Eion = 20- 40 eV




HIPIMS has been implemented successfully on industrial scale machines

HIPIMS discharges produce metal ions charged up to 2+ for Ti, Cr and Nb

The metal ion–to–neutral ratio increases continuously as a function of peak power

Metal ion etching by HIPIMS promotes local epitaxial growth and improves theadhesion of coatings without incorporation of droplets

HIPIMS pretreatment improves the corrosion performance due to defect-freeinterface of multilayer films

High Power Impulse Magnetron Sputtering (HIPIMS)

A. P. Ehiasarian

Nanotechnology Centre for PVD Research,Materials and Engineering Research Institute,Sheffield Hallam University, UK




Recommended literature

1. Kelly, P.J., Arnell, R.D. (2000) Magnetron Sputtering: A Review of Recent Developments and Applications, Vacuum, 56, 159-172.

2. Safi, I. (2000) Recent Aspects Concerning DC Reactive Magnetron Sputtering of Thin Films: a Review, Surf. Coat. Technol. 127, 203-219.

3. Musil, J. (1998) Recent Advances in Magnetron Sputtering Technology, Surf. Coat. Technol. 100/101, 280-286.

4. Bunshah, R.F. (1991) Handbook of Deposition Technologies for Films and Coatings: Science, Technology and Applications, Second Edition, Noyes Publ., New Jersey

5. Wasa, K., Hayakawa, S. (1991) Handbook of Sputter Deposition Technology, Noyes Publ., Park Ridge, New Jersey.

6. S. M. Rossnagel, J.J. Cuomo & W.D. Westwood (eds.) Handbook of Plasma Processing Technology, Noyes Publ. (1990) Park Ridge, New Jersey

physical vapour deposition of thin film coatings

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