Entfernung von Kohlenwasserstoffschichten aus Gräben und ...home.uni-leipzig.de/iom/muehlleithen/2008/schwarz_selinger.pdfschwarz-selinger.ppt, © Thomas Schwarz-Selinger, 05. März

schwarz-selinger.ppt, © Thomas Schwarz-Selinger, 05. März 2008

Max-Planck-Institutfür Plasmaphysik

Entfernung von Kohlenwasserstoffschichten aus Gräben und Spalten mittels Sauerstoffplasmen:

Das delikate Zusammenspiel von Physik und Chemie

Thomas Schwarz-Selinger, Wolfgang Jacob

XV. ErfahrungsaustauschOberflächentechnologie mit Plasma- und Ionenstrahlprozessen

Mühlleithen 05. März 2008



Removal of hydrocarbons from gaps with oxygen plasmas:

the delicate interplay between physics and chemistry

Thomas Schwarz-Selinger, Wolfgang Jacob

XV. ErfahrungsaustauschOberflächentechnologie mit Plasma- und Ionenstrahlprozessen

Mühlleithen 05. März 2008


motivation

Thermonuclear Fusion Research

as longs as carbon will be a first wall material carbon redeposition will be a safety issuein terms of tritium inventory

For the next step fusion device ITERfilm removal is mandatory to guaranteelong term operation

Oxygen glow discharge cleaning was proposed as one candidate

Question to address: are low pressure/temperature O2 plasmas suited ?

ratesintegration (dc-glow, rf, microwave …)compatibility (oxide formation, …)…mechanism

ASDEX Upgrade


challenge for film removal: gaps everywhere

plasma exposed surface ≈ remote surfaces

EU Prototype ofInner Vertical Targetwith CfC & W Armouranimated view inside ITER


erosion of carbon in tile gap structures by oxygen plasmas

1) a-C:H deposition on Si (001)

2) erosion of pre-deposited tile gap structures in oxygen discharges

3) analysis ex-situ by ellipsometry expectation:not possible to clean

deep trenches

plasma depositeda-C:H

Si

model system for redeposited films: amorphous, hydrogenated carbon (a-C:H)

size ≈ mean free path

size ≈ λDebye




1) a-C:H deposition on Si (001)

2) erosion of pre-deposited tile gap structures in oxygen discharges

3) analysis ex-situ by ellipsometry expectation:not possible to clean

deep trenches

plasma depositeda-C:H

Si

size ≈ mean free path

size ≈ λDebye


erosion of carbon by oxygen

CO, CO2 , H2O O2, O2+ , O+ , O0 , O3

candidates

at elevated temperature: O2 ( > 650 K, oxidation)

at RT: O2 & ions (chemical sputtering: yields > 1)

O+, O2+ (chemical sputtering : yields > 1)

O0 (chemical erosion: yields << 1)

O3 (chemical erosion: yields << 1)

a-C:H




different oxygen plasmas

ECR afterglow (thermal energies)

ECR plasma (ion energy ≈ 15 eV)

CCP mode (ion energy ≈ 300 eV)

2.45 GHz

magneticcoils

ECRPlasma

ellipsometry

laser (633 nm)

blocking plate

analysis by ellipsometry

before exposure 2D scanduring exposure locallyex-situ 2D scan of all surfaces




different oxygen plasmas

ECR afterglow (thermal energies)

ECR plasma (ion energy ≈ 15 eV)

CCP mode (ion energy ≈ 300 eV)

2.45 GHz

magneticcoils

r f

ECRPlasma

ellipsometry

laser (633 nm)

rf biasedsubstrate





prior to exposure

gap: widths 4 mm, 2 mm, 1 mm, 0.5 mm

trench depth: 19 mm

exposure to O2 afterglow




erosion in ECR oxygen afterglow (thermal particle energies)

efficiency is vastly reduced inside the tile gaps !

-10 0 10 20 30 40

800

600

400

200

0

ECRafterglow

erod

ed fi

lm th

ickn

ess

botto

m p

late

(Å)

lateral position (mm)

gap width4 mm 2 mm 1 mm 0.5 mm

undisturbed flat surface:

1200 Å

ellipsometry



ellipsometry

efficiency is vastly reduced inside the tile gaps !

-10 0 10 20 30 40100

50

0

-50

ECRafterglow

erod

ed fi

lm th

ickn

ess

botto

m p

late

(Å)


gap width4 mm 2 mm 1 mm 0.5 mm

efficiency drops further for smaller gaps !

(NO collisions to reach the bottom,field of view, …)



0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

10

20

30

40

50

60

70

80

90

100

erod

ed fi

lm th

ickn

ess

botto

m p

late

(Å)

gap width (mm)

ECR afterglow

efficiency of bottom erosionincreases linearly with gap width !

(neutral transport)

ellipsometry



ellipsometry

0 1 2 3 40

20

40

60

80

100

botto

m e

rosi

on (%

of f

lat s

urfa

ce)

gap width (mm)

ccp 300 eV ECR 15 eV ECR afterglow

efficiency of bottom erosionincreases with ion energy !



ellipsometry

0 6 12 180

200

400

600ECR

afterglow

erod

ed fi

lm th

ickn

ess

side

wal

ls (Å

)

penetration depth (mm)

/ 4 mm (r/l) / 2 mm (r/l) / 1 mm (r/l) / 0.5 mm (r/l)

side wall erosion drops faster for smaller gaps !



bottom erosion ≈ side wall erosion

30 35

0

-200

0 200 400 600

18

16

14

12

10

8

6

4

2

0600 400 200 0

erod

ed fi

lm th

ickn

ess

(Å)


gap width0.5 mm

ECRafterglow

pen

etra

tion

dept

h (m

m)

eroded film thickness (Å)

expected:



0 5

0

-200

0 200 400 600

18

16

14

12

10

8

6

4

2

0600 400 200 0

erod

ed fi

lm th

ickn

ess

(Å)


gap width4 mm

ECRafterglow

pen

etra

tion

dept

h (m

m)


expected:

bottom erosion ≈ 4 times side wall erosion


erosion in ECR oxygen plasma (15 eV ion energy)

bottom erosion ≈ 4 times side wall erosion

0 5

500

250

0

-250

0 250 500 750

18

16

14

12

10

8

6

4

2

0750 500 250 0

erod

ed fi

lm th

ickn

ess

(Å)


gap width4 mm

ECR15 eV

pen

etra

tion

dept

h (m

m)


expected:


erosion in ccp oxygen plasma (300 eV ion energy)

0 5

750

500

250

0

0 250 500 750

18

16

14

12

10

8

6

4

2

0750 500 250 0

erod

ed fi

lm th

ickn

ess

(Å)


gap width4 mm

CCP300 eV

pen

etra

tion

dept

h (m

m)


bottom erosion > 10 times side wall erosion


erosion in ccp oxygen plasmas (300 eV ion energy)

30 35

200

0

-200

0 200 400 600

18

16

14

12

10

8

6

4

2

0600 400 200 0

erod

ed fi

lm th

ickn

ess

(Å)


gap width0.5 mm

CCP300 eV

pen

etra

tion

dept

h (m

m)


bottom erosion > 8 times side wall erosion


summary

erosion rates on flat surfaces much higher than in gaps

eroded amount drops with gap width

erosion on lower side walls smaller than on bottom surface (esp. for 300 eV)

(but side wall erosion dominates total erosion)

bond breaking + chemical reactivity (chemical sputtering)

aim to reach deep inside the gaps: high flux of species with low reactivity !

low-T oxygen plasmas are not suited to reach deep gaps


outlook

erosion of tile gap structures in different low-T plasmas

erosion of cavities in the afterglow

erosion of a-C:H with ozone

erosion with atomic oxygen



Documents

Entfernung von Kohlenwasserstoffschichten aus Gräben und ...home.uni-leipzig.de/iom/muehlleithen/2008/schwarz_selinger.pdfschwarz-selinger.ppt, © Thomas Schwarz-Selinger, 05. März