11

Influence of Tungsten/Carbon Interactions On Carbon Erosion Behavior In D2 Plasma

 

Nick Lyon, Florian Weilnboeck, and Gottlieb S. OehrleinDepartment of Material Science and Engineering and

Institute for Research in Electronics and Applied PhysicsUniversity of Maryland, College Park, Maryland, 20742

Russ P. Doerner Center for Energy Research, University of California – San Diego

July 2009

2

Outline

Experimental apparatus and diagnostics Erosion of hard a-C:H in deuterium plasma Influence of W near-monolayer coverage on a-

C:H erosion Conclusions

3

University of Maryland Cluster System for Plasma Processing of Materials

Multi-TechniqueSurface Analysis

Chamber(XPS, AES, ...)

Evaporator

Capacitively Coupled Plasma (CCP) Reactor

LoadLock I

ICP Reactor

LoadLock II

Inductively

Coupled PlasmaReactor Evaporator

Numerous Plasma and SurfaceDiagnostic Techniques Shared

Between All Systems

4

Experimental Setup Inductive Power 600W to 800W (13.56 MHz)

Operating Pressure 10 mTorr Erosion

RF Bias -100 V, 3.7 MHz

CH4, D2, Ar

Total gas flow = 40 sccm

Planar Coil ICP

Network

RF power

RF bias power

Laser Detector

Confinement Ring

In situ ellipsometry real time monitoring of processesXPS: surface characterization

5

ICP Device Measurements used as basis of computer simulations and model validation by several major

plasma modeling groups – Sandia National Labs, M. J. Kushner In turn has helped us refine the measurements

Xi Li, Li Ling, X. Hua and G. S. Oehrlein, Y. Wang, A. V. Vasenkov and M. J. Kushner, J. Vac. Sci. Technol. A 22, 500 (2004). V. Vasenkov, Xi Li, G. S. Oehrlein, and M. J. Kushner, J. Vac. Sci. Technol. A 22, 511 (2004).

Geometry and B-Field Measurements

6

Process Sequences to be Discussed

D2 erosion of

• a-C:H films• a-C:H + in-situ deposited W (below and

above 1 monolayer)• a-C:H + in-situ deposited W above 1

monolayer and air-exposed for oxidation

25 30 35 4020

30

40

50

60

70

80

De

lta [d

eg

.]

Psi [deg.]7

WOx on W2nm Steps

Deuteration/Roughening5 nm steps

W coverage 1 mL (0.3nm) steps

Ellipsometry Interpretation

a-C:H

deposition

erosion

8

Erosion of a-C:H Film in D2 Plasma

D2 Plasma

32 33 34 35 3640

45

50

55

De

lta [D

eg

.]

Psi [Deg.]

Deposition Fit Erosion Data Model of soft Layers

11 12 13 14 15268

272

276

280

284

De

lta [d

eg

.]

Psi [deg.]

Deposition Data Erosion Data Model of soft layers

Deposition

Deposition

Erosion

Erosion

9

Simulation of a-C:H:W Materials in ReactorExperimental

• W sputter onto a-C:H film• Ar 10 mTorr 30 sccm• 600 W Source Power• -100V bias

a-C:H

Ar

W

C, H

a-C:H-W

D2

W

C, H, W

• D2 erosion of a-C:H/W films• D2 10 mTorr 30 sccm• 600 W Source Power• -100 V bias

Erosion of W/a-C:H Film in D2 Plasma

0 20 40 600

50

100

150

200 a-CH Deposition Deuterium Erosion

D

elta

[Deg

.]

Psi [Deg.]

Erosion start

Erosion stop

120s

240s

0 10 20 30 40 50

30s W 40mTorr

Inte

nsity

[arb

. uni

ts]

Binding Energy [eV]

valence band

0 10 20 30 40 50

30sW 40mTorr240s D2

Inte

nsity

[arb

. uni

ts]

Binding Energy [eV]

valence band

0 10 20 30 40 50

30s W 40mTorr120s D2

Inte

nsity

[arb

. uni

ts]

Binding Energy [eV]

valence band

0 10 20 30 40 50

30sW 40mTorretch stop

Inte

nsi

ty [a

rb. u

nits

]Binding Energy [eV]

valence band

11

Impact of W Monolayer Coverage On a-C:H Erosion

0.0 0.5 1.0 1.50

5

10

15

20

25

30

35

40

45

Ero

sio

n R

ate

[nm

/min

]

Monolayer W Coverage0.0 0.5 1.0 1.50

30

60

90

Monolayer W Coverage

Tim

e T

o r

em

ove

10

nm

a-C

H [s

]

0 50 100 1500

10

20

30

40

0 mL W 0.48 mL W 1.16 mL W

a-C

H R

emov

ed [n

m]

Exposure Time [s]

0 50 100 1500

25

50

75 0 mL W 0.48 mL W 1.16 mL W

a-C

H T

hic

knes

s [n

m]

Exposure Time [s]

~8x lower

28 30 32 34 36 38 40

W 4f30s 40mTorretch stop D2 erosion

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]28 30 32 34 36 38 40

W 4f30s 40mTorr4min D2 erosion

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]28 30 32 34 36 38 40

W 4f30s 40mTorr2 min D2 erosion

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]28 30 32 34 36 38 40

W 4f30s 40mTorr

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]

280 282 284 286 288 290

C 1s30s 40mTorr

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]280 282 284 286 288 290

C 1s30s 40mTorr 2min D2 erosion

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]280 282 284 286 288 290

C 1s30s 40mTorr 4min D2 erosion

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]280 282 284 286 288 290

C 1s30s 40mTorr groundedetch stop

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]

XPS Time Sequence:After W Deposition, 2min D2, 4min D2, Erosion Stop

W depositionRMS=2.4 nm

2min D2RMS=3.4 nm

Etch stop D2RMS=9.24 nm

4min D2RMS=17.38 nm

24 28 32 3620

40

60

80

100 Deposition Data Erosion Data aCH + W aCH + Rough Layer + W aCH + Deuteration

D

elta

[de

g.]

Psi [deg.]

PlasmaStart

Roughness Formation Dominates Surface Modification

15

Real-Time Roughness Measurements

0.0 0.5 1.0 1.50

15

30

45

60

75

Max

imum

Ro

ugh

ness

[nm

]

Monolayer W Coverage0 100 200 300

0

20

40

60

80 20 mTorr Ar W Sputter 40 mTorr Ar W Sputter 40 mTorr W Grounded Sputter 50 mTorr Ar W Sputter 50 mTorr W Grounded Sputter

Rou

gh L

ayer

Thi

ckne

ss [n

m]

Plasma Time [s]

27 30 33 36

25

50

75

100a-CH depositionDeuterium erosionW on a-CHMaximum Roughness

De

lta [d

eg

.]

Psi [deg.]

1.2nm WWOx W

Roughness 40 nm

0 10 20 30 40 50

30s 40mTorrgrounded

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]

valence band

0 10 20 30 40 50

30s 40mTorrgrounded120s D2 erosion

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]

valence band

Fate of Oxidized W During a-C:H Erosion

0 s

120 s D2

120 s D2

0 s

28 30 32 34 36 38 400

1000

2000

3000

4000

5000

6000

7000

8000

9000W 4f30s 40mTorr grounded

2min D2 erosion

Inte

nsi

ty [C

PS

]

Binding Energy [eV]

28 30 32 34 36 38 400

1000

2000

3000

4000

5000

6000

7000

8000

9000W 4f30s 40mTorr grounded

Inte

nsi

ty [C

PS

]

Binding Energy [eV]

Oxygen removal after grounded deposition during D2 erosion

280 282 284 286 288 290

0

1000

2000

3000

4000

5000C 1s30s 40mTorr grounded

Inte

nsi

ty [C

PS

]

Binding Energy [eV]

280 282 284 286 288 290

0

1000

2000

3000

4000

5000C 1s30s 40mTorr grounded

2min D2 erosion

Inte

nsi

ty [C

PS

]

Binding Energy [eV]

526 528 530 532 534 536 538

0

2000

4000

6000

8000

10000

12000O 1s30s 40mTorr grounded

Inte

nsi

ty [C

PS

]

Binding Energy [eV]

526 528 530 532 534 536 538

0

2000

4000

6000

8000

10000

12000O 1s30s 40mTorr grounded

2min D2 erosion

Inte

nsi

ty [C

PS

]

Binding Energy [eV]

Optical Emission Spectroscopy

Although W emission is not detected for D2 plasma, exposure of test coupons show that W transport during D2 plasma exposure of W takes place for conditions employed

0 10 20 30 40 50

Inte

nsi

ty [a

rb. u

nits

]

Binding Energy [eV]

valence band 10min D2 erosionSi sample grounded

19

Conclusions

W monolayer coverage of a-C:H has profound influence on erosion behavior, including

• Initial retardation of erosion

• Lower steady-state erosion rate

• Slow removal of W

• Microscopic blocking of sites and surface roughening The complex surface processes taking place can be efficiently

studied by a combination of

• Real-time

• Post-plasma

surface diagnostics

20

Acknowledgements

We gratefully acknowledge financial support of this work by the Department of Energy