Process of magnetron sputtering

L. Marot - ITPA 12 meeting, Princeton March 28, 2007 n° 1/21

Process of magnetron sputtering

Laurent Marota, Grégory De Temmermana b; Andrey Litnovskyb, Grégory Covarelc and Peter Oelhafena

Rhodium coated mirrors deposited

by magnetron sputtering for first mirror

a Institute of Physics, University of Basel, Switzerlandb now: Center for Energy Research, University of California at San Diego, USAc Institut für Plasmaphysik, Ass. EURATOM, TEC, Forschungszentrum Jülich, Germanyd Mechanical Laboratory, University of Haute-Alsace, France


500 1000 1500 200030

40

50

60

70

80

90

100

SS

W

MoRh

Cu

Ref

lect

ivit

y (%

)Wavelength (nm)

Motivation

1Handbook of optical constants of solids, ed. E.D. Palik, Acad. Press, 1985 and 1991

Calculated with (n, k) from [1]

Rhodium is a very attractive

option for first mirror material:

Good reflectivity

High melting point (1966 °C)

Low sputtering yield (high Z)

High price of the raw material calls for developing thin film technology

Existing studies made with electro-deposition or magnetron

(Reference: G Maddaluno 11th ITPA, N.V Klassen 10th ITPA)


Routine process:

Total time deposition: 25 hours

Total Rh thickness deposited:

35 microns

Rhodium layeron copper

[2] Characterization of magnetron sputtered rhodium films for reflective coatings , L. Marot et al, submitted to Surface Coating Technology


Vacuum deposition technique

Typical deposition conditions:

Pressure: 0.6 Pa - argon gas DC power, 25 W (U = -225 V / I = 0.11 A ) Deposition rate: 0.6 nm / s Deposition on silicon and metallic

substrates

Investigated conditions:

Pressure, Power applied to the target,

Deposition temperature [2]


No impurities (carbon, oxygen, argon) were detected by in-situ XPS on the surface after deposition

Homogeneous rhodium film with dense columnar structure (up to 2.4 m thick)

SEM cross section observation of rhodium film deposited on Si at RT

SEM cross section observation of rhodium film deposited on Si at 350 °C

Characterization of the layer / 1

1.2 m 1.8 m


500 1000 1500 2000 25000.0

0.5

1.0

1.5

2.0

Mo before deposition Ra = 4 nm

Rh after deposition on Mo Ra = 4.2 nm

Dif

fuse

ref

lect

ivit

y (%

)

Wavelength (nm)

Ra = 4.2 nm / Before deposition 4 nm

Crystallite size = 10 nm

SEM observation of a rhodium layer (1,5 m) on molybdenum


Diffuse reflectivity measured before and after deposition

No polishing after deposition

Low roughness after deposition

Film roughness depends on the initial substrate

roughness


600 1200 1800 240065

70

75

80

85

90

Sp

ec

ula

r re

fle

cti

vit

y (

%)

Wavelength (nm)

Deposition RT Deposition 170°C Deposition 350°C


RSpecular = RTotal - RDiffuse

Specular reflectivity measured on Rh layer deposited on stainless steel at different temperatures

Film roughness depends on the deposition temperature

0 100 200 300 4000.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

350 °C

170 °C

RT

Roughness

Afte

r D

eposi

tion

Roughness

Befo

re D

eposi

tion

Temperature (°C)


30 40 50 60 70 80 90

84.6°70.1°

47.9°

41.2°

Rh(311)Rh(220)Rh(200)

Rh(111)

Rel

ativ

e In

ten

sity

2 (degrees)

X-ray diffraction measurements:

Polycrystalline, no specific texture, no specific orientation for the grains

Grain size around 10 nm (Calculated by

Scherrer formula)


X-ray diffraction pattern of deposited rhodium film

Nanohardness (3 mN) measurements:

The hardness of a rhodium layer (1.7 m thick)

is 9.2 GPa, in comparison to 1.2 GPa for the

annealed bulk rhodium

Influence of the hardness for

erosion?

Rel

ativ

e In

tens

ity


Layer deposited on metallic substrate (Mo, Cu, stainless steel) for layer thickness > 1 m

Total reflectivity measured on Rh layer deposited on metallic substrates

No influence of the

substrates on the

optical properties

600 1200 1800 2400

65

70

75

80

85

90

95

To

tal r

efle

cti

vity

(%

)

Wavelength (nm)

Rhodium reference [1] Rh on Stainless Steel Rh on Copper Rh on Molybdenum

Influence of the substrate on the optical properties


Stainless Steel 273 30 < 2

Critical Load (N)

1.5

8.8

8.3Stainless Steel 273 350

Stainless Steel 273 170 9.5

Molybdenum 261 30

Copper 122 30

SubstrateHardness Vickers

Hv 0.1Temperature of deposition (°C)

Scratch test measurements: load from 0 to 20 N at a rate of 10 N·min-1)

Influence of the substrates for the adhesion of the coating

Main part of a scratch track of rhodium film sample deposited at 170°C on stainless steel

The adhesion

properties increase

with the substrate

hardness

First crack

1.7 N 4 N

First breakthrough

Lc = 9.5N

First pad adhering Worn out30 m

19.5 N

Scratch direction


0 20 40 60 80

50

60

70

80

90

100

Total reflectivity

Lambda = 660 nm

s p

Ref

lect

ivit

y (%

)

Angle of incidence (°)

Reflectivity at 40, 50, 60, 70 and 80° for s and p polarizations at 660 nm of rhodium layer

For some laser diagnostics (LIDAR, MSE) the polarisation of the linearly polarised laser radiation is relevant

Measurement of polarization reflectivity by ellipsometry


600 1200 1800 240055

60

65

70

75

80

85

90

95

Rhodium reference Rh (1000nm) on Stainless Steel Same layer after 10 times annealing Rh (1250nm) on Molybdenum Same layer after 10 times annealing

To

tal r

efle

ctiv

ity

(%)

Wavelength (nm)

Annealing cycles: 10 times @ 5h at 200 °C in air

Effect of annealing cycles on the mirror reflectivity

The optical

observations did not

reveal any

modification or

delamination of the

layer

Total reflectivity of Rh layer before and after annealing cycles


Laboratory experiments for erosion by deuterium ions of rhodium mirrors [4]

Deuterium RF plasma with a graphite hollow cathode

Bias on sample: - 300 V to

control impinging ions energy

Pressure: 6 Pa

Time of plasma: 13 h

Fluence: 2×1020 ions/cm2

Laboratory experiments for erosion / 1

[4] Same process described by G. De Temmerman et al, 10th ITPA

Setup for D2 plasma sputtering, for rhodium deposition and in situ XPS


Post Cleaning D2 RF Plasma

-100 V / 30 min / 300 °C


Total reflectivity measured on Rh layer (1.8 m) deposited on Mo

Reflectivity after D2 sputtering

Weight measurements

allow the determination

of the eroded tickness:

375 nm eroded

500 1000 1500 2000 2500

55

60

65

70

75

80

85

90

To

tal r

efle

ctiv

ity

(%)

Wavelength (nm)

Rhodium layer (1.8 m) on Mo Same layer after Deuterium Plasma

500 1000 1500 2000 2500

55

60

65

70

75

80

85

90

To

tal r

efle

ctiv

ity

(%)

Wavelength (nm)

Rhodium layer (1.8 m) on Mo Same layer after Deuterium Plasma Post Cleaning after Deuterium Plasma

Carbon on the surface (measured by XPS)


500 1000 1500 2000 25000.00

0.25

0.50

0.75

1.00

1.25

1.50

Rh after deposition on Mo Ra = 4.2nm Rh after D2 Plasma Ra = 2.8 nm Rh after Post D2 Cleaning Ra = 5.6 nm

Dif

fuse

ref

lect

ivit

y (%

)

Wavelength (nm)

Ra = 4.2 nm

Ra = 2.8 nm

Ra = 5.6 nm

Diffuse reflectivity measured before, after D2 sputtering and after post cleaning

500 1000 1500 2000 25000.00

0.25

0.50

0.75

1.00

1.25

1.50

Rh after deposition on Mo Ra = 4.2nm Rh after D2 Plasma Ra = 2.8 nm Rh after Post D2 Claning Ra = 5.6 nm

Dif

fuse

ref

lect

ivit

y (%

)

Wavelength (nm)


No significant change of roughness after erosion



Total reflectivity measured on Rh layer deposited on Stainless Steel and Copper

Same experiment on 2 layers (> 1 m) deposited on Stainless Steel and Copper

After erosion by

deuterium ions the

reflectivity is constant

500 1000 1500 2000 2500

50

60

70

80

90

To

tal r

efle

ctiv

ity

(%)

Wavelength (nm)

Rh on SS Rh on SS After D2 Plasma

Rh on Cu Rh on Cu After D2 Plasma

500 1000 1500 2000 2500

50

60

70

80

90

To

tal r

efle

ctiv

ity

(%)

Wavelength (nm)

Rh on SS Rh on SS After D2 Plasma Rh on SS After Cleaning Rh on Cu Rh on Cu After D2 Plasma Rh on Cu After Cleaning


TEXTOR, Jülich, Germany

• 19 shots, ~ 210 plasma seconds

• Mirror temperature 300 – 500 °C

• D+ energy: ~ 250 - 300 eV

• Fluence = 2x1020 ions/cm2

Mirrors exposed in the Scrape-Off layer plasma of TEXTORRh Uni.

Basel Rh [5] SC Mo

[5] G Maddaluno 11th ITPA

Exposure of Rh mirrors under erosion conditions in TEXTOR


No significant change of the XRD measurements

=> No crystallographic change (temperature exposure 300 – 500

°C)

=> No delamination

XRD measurements before and after exposure


30 40 50 60 70 80 90

Before Exposure After Exposure

Rh(311)Rh(220)Rh(200)

Rh(111)

Rel

ativ

e In

tens

ity

2 (degrees)


Total reflectivity measured before and after exposure

Reflectivity of mirrors exposed in the Scrape-Off layer plasma of TEXTOR

Eroded thickness for rhodium: 440 nm

SIMS / XPS after exposure: Mo and/or MoCand MoO ( 5 - 8 %)and Amorphous Carbon

Rh Basel



500 1000 1500 2000250055

60

65

70

75

80

85

90

Sp

ecu

lar

refl

ecti

vity

(%

)

Wavelength (nm)

Rh Basel Before Exposure Ra = 6.3 nmRh Basel After Exposure Ra = 8.9 nm

Possibility of mirror

cleaning

Same Post Cleaning experiment with : D2 RF plasma -100 V / 45 min / 250 °C

10000.5

1.0

1.5

2.0

2.5

3.0

3.5

Rh Basel Before Exposure Ra = 6.3 nm Rh Basel After Exposure Ra = 8.9 nm Post Cleaning D2 Plasma Ra = 6.5 nm

250 °C / -100 V / 45 min

Dif

fuse

ref

lect

ivit

y (%

)

Wavelength (nm)


600 1200 1800 24000.5

1.0

1.5

2.0

2.5

3.0

3.5

Dif

fuse

ref

lec

tivi

ty (

%)

Wavelength (nm)

600 1200 1800 24000.5

1.0

1.5

2.0

2.5

3.0

3.5

Dif

fuse

ref

lect

ivit

y (%

)

Wavelength (nm)

500 1000 1500 200025000.5

1.0

1.5

2.0

2.5

3.0

3.5

D

iffu

se r

efle

ctiv

ity

(%)

Wavelength (nm)

Rh Basel Before Exposure Ra = 6.3 nmRh Basel After Exposure Ra = 8.9 nmPost Cleaning D2 Plasma Ra = 6.5 nm


No impurities were detected by XPS on the surface after deposition

Homogeneous rhodium film with dense columnar structure ( up to 2.4 m thick) with small grain size (~10 nm)

Low roughness after Rh deposition (depending on the substrates)

No effect of annealing treatment in air on the reflectivity(10 times @ 5h at 200 °C in air)

Good adhesion of coating on hard substrate (measured by scratch test)

Rh-coating has survived the exposure in erosion-dominated conditions in laboratory experiment and in TEXTOR

Conclusion


On going

Erosion test for high D+ energy :500 - 600 eV (Karkov Institute, V. Voitsenya)

Measurement of the sputtering yield of rhodium film (to compare with that of bulk Rh)

Effect of baking cycles (400 °C) in vacuum

Thank you for your attention

Questions ?



Laurent Marota, Grégory De Temmermana b; Andrey Litnovskyb, Grégory Covarelc and Peter Oelhafena

Rhodium coated mirrors deposited

by magnetron sputtering for first mirror

a Institute of Physics, University of Basel, Switzerlandb now: Center for Energy Research, University of California at San Diego, USAc Institut für Plasmaphysik, Ass. EURATOM, TEC, Forschungszentrum Jülich, Germanyd Mechanical Laboratory, University of Haute-Alsace, France


500 1000 1500 2000 250050

55

60

65

70

75

80

85

90

95

100

Rh Basel Before Exposure Rh Basel After Exposure SC Mo Before Exposure SC Mo After Exposure Rh ENEA After Exposure

T

ota

l ref

lect

ivit

y (%

)

Wavelength (nm)Total reflectivity measured before and after exposure

Mirrors exposed in the Scrape-Off layer plasma of TEXTOR


Documents

Process of magnetron sputtering