master class: electronegative plasmas september 28-30

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Master Class: Electronegative Plasmas September 28-30

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Page 1: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Page 2: Master Class: Electronegative Plasmas September 28-30

Diagnostics for Electronegative Plasmas

Winfred Stoffels

Page 3: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Outline

Introduction

Standard diagnostics

Specific diagnostics

Using negative ion diagnostics for neutrals

Dusty plasma

Page 4: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Electronegative plasmas

Page 5: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Example plasma: capacitively coupled

radiofrequency low pressure plasma

Page 6: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Properties of electronegative plasmas

Negative ions

Charged

Heavy

Trapped in the discharge polymerization

Ne + N_ = N+

Changed ionization and loss rates plasma

quenching (switches)

Changed transport different I-V characteristics

Page 7: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Page 8: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Standard diagnostics show influence of negative ions

Approach

Use electropositive plasma as comparison

Measure as a function of dilution

Beware that transition electropositive to electronegative can occur at small dilutions

Page 9: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

We can use traditional diagnostics to follow negative ions: resistance

Page 10: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

We can use traditional diagnostics to follow negative ions: optical emission

Page 11: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

We can use traditional diagnostics to follow negative ions:

Charge neutrality

Page 12: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

We can use traditional diagnostics to follow negative ions:

Transport

Page 13: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

We can use traditional diagnostics to follow negative ions:

Plasma structure and current

Page 14: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Conclusion

Transition from electropositive to electronegative plasma

occurs at small dilution

Visible in:

Resistance

Voltage

Current

Emission

Charge balance

Plasma and sheath structure

Measurable by traditional plasma diagnostics

Page 15: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Outline

Introduction

Standard diagnostics

Specific diagnostics

Using negative ion diagnostics for

neutrals

Dusty plasma

Page 16: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

OutlineIntroduction

Standard diagnostics

Specific diagnostics

Probes

Mass spectrometry

Photo detachment

Using negative ion diagnostics for neutrals

Dusty plasma

Page 17: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Direct negative ion measurement with Probes(Amemiya)

+ simple and cheap setup

- “not” species selective

- difficult to measure

Negative ion current is visible in the second derivative of the probe characteristic as a small peak just above 0 V.

Page 18: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Ion Mass Spectrometry (QMS, TOF, …)

+ Well known technique

+ Direct ion measurement

+ Mass selective most often chemical identification possible

+ Sensitive

- Detects a flux not a density plasma model is needed

- Mass dependent transmission model is needed

- Poor spatial and temporal resolution

Page 19: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Ion Mass Spectrometry (negative ions)

- Negative ions are trapped in glow

Solutions:

positive bias disturbs plasma

typical approach in ion sources

Pulse plasma

» Afterglow measurement

» Diffusion model needed

Page 20: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Page 21: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Page 22: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Pulse plasma.

Negative and positive ions in SiH4 plasma

(after Howling)

Page 23: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

direct measurement : Surface produced negative ions

Example:

O- produced at kathode and measured at anode

Page 24: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

OutlineIntroduction

Standard diagnostics

Specific diagnostics

Probes

Mass spectrometry

Photo detachment

Using negative ion diagnostics for neutrals

Dusty plasma

Page 25: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Photodetachment

X- + hv X + e The negative ion is transformed into a free electron

Lasers provide the needed photon

Electron can be measured easily

Optogalvanic

Probe

Microwave resonance

Electron and ion kinetics can be measured

Page 26: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Photodetachment

X- + hv X + e+ Local measurement

+ High time resolution (pulsed laser)

+ Kinetic information

+/- Specific on species depends on threshold

- Electron diagnostic needed (and its minus points)

- Need to check for other laser induced effects (ionization of

neutrals)

Page 27: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Selectivity depends on electron affinity EA of F- 3.4 eV (364nm)

(Haverlag)

Page 28: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

•Photodetachment can be done in two regimes

linear +less disturbing- cross section must be known

saturation+ independent of cross section-hard to acchieve

After Bacal

Page 29: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

+ easy

+/- spatial information modified by transport true plasma

- difficult to make quantitative

Photodetachment in combination with Optogalvanic method

Page 30: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Page 31: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Photodetachment in combination with probe(Bacal)

+ easy

- need theory

- laser hits probe and can result in photo electrons

from probe

Page 32: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Photodetachment in combination with probe(Bacal)

Page 33: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

+ quantitative

+ no model needed

+ gives information on ion kinetics

+/- line of sight

- complex

Photodetachment in combination with microwave resonance(Eindhoven)

Page 34: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Photodetachment in combination with microwave resonance

Page 35: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

negative charge in dusty plasma

Beginning: only negative ions

ne = 1013 m-3

Slow electron capture

After 1 sec:

charged particles

ne = 1014 m-3

Fast electron capture

Page 36: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

particle charge: measured by photodetachment

As particles grow:

-Charge on particles increases

-Recharging time decreases

Page 37: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

OutlineIntroduction

Standard diagnostics

Specific diagnostics

Probes

Mass spectrometry

Photo detachment

Using negative ion diagnostics for neutrals

Dusty plasma

•Optogalvanic

•Probe

•Microwave resonance

Page 38: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Electron Attachment Mass Spectrometry

Use electronegative character to analyze neutrals

XY + e XY- or X- + Y

+ negative ions can be mass specific detected by QMS

+ lower electron energy needed less fragmentation

+ resonant process possible to selectively create negative

ions

Page 39: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Electron Attachment Mass Spectrometry

Page 40: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Polymerization in C2F6 plasma:

Negative ion fragments Positive ion fragments

Page 41: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Combinations of Mass spectrometry and photodetachment

After

Boesl, Muenchen

Page 42: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Combinations of Mass spectrometry and photodetachment

Page 43: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Figure 1: Partial cross section for the process K- + γ - K(5s) + e- in the photon energy range from

4.19 eV to 4.26 eV. Curves: present results in dipole velocity (solid) and dipole length

(dotted) approximations

After Chien-Nan Liu

Page 44: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

OutlineIntroduction

Standard diagnostics

Specific diagnostics

Probes

Mass spectrometry

Photo detachment

Using negative ion diagnostics for neutrals

Dusty plasma

Page 45: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Page 46: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Page 47: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Solar Cells

m etalnegatively doped layer

intrinsic a-S i:H

positively doped layertransparent conductive oxide

glass

-

+

incom ing light

Page 48: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

a solar cell

Consists of multiple layers with different functions

Produced in low pressure RF plasma

Layer is an amorphous hydrogen rich silicon layer

wall

Amorphous H-Si

rf

C

Page 49: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

The Staebler-Wronski effect

0 50 100 150 2000

2

4

6

8

10

pm Si

Eff

icie

ncy

(%

)

Time (hours)

He 250oC Std 250oC

Std 150oC

Std 100oC

After Roca i Cabarrocas et al, Ecole Polytechnique, Palaiseau, France

• Solar cell degradation induced by exposition to sun light

• Initial degradation during the first 200 kWh/m2

• Embedded nanocrystalline structures increase solar cell lifetime and efficiency (pm-Si)

Page 50: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Solar Cells

Roca i Cabarrocas et al, Thin Solid Films 403-404 (2002) 39-46

cr:Si a:Si

pm:Si

m etalnegatively doped layer

intrinsic a-S i:H

positively doped layertransparent conductive oxide

glass

-

+

incom ing light

Page 51: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Dust Particles

0.1nm 1nm 10nm 100nm 1μm

molecule macro-molecule nano-particle agglomerate powder

α-regime γ´-regime

amorphous not usable

Page 52: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

•Neutral chemistry

•Particles

•Electrons and ions

Internal plasma parameters:

Page 53: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

•Neutral chemistry

•Emission spectroscopy: ASDF, dissociation

•RGA, FTIR, LIF: dissociation, polymerization, ASDF

•Infrared absorption spectroscopy: dissociation, polymerization, temperature

•Infrared CRD: radical densities

•Ellipsometry: surface chemistry

•Particles

•Electrons and ions

Results available

Available if needed

Under construction

Internal plasma parameters:

Page 54: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

•Neutral chemistry

•Particles

•Electrons and ions

•Microwave resonance: electron density

•Photodetachment: negative ion density

•Doppler resolved LIF, energy resolved QMS: IEDF, E-field

•Langmuir probe, Thomson scattering: EEDF

Results available

Available if needed

Under construction

Internal plasma parameters:

Page 55: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

•Neutral chemistryResults available

Available if needed

Under construction

•Particles

•Mie Scattering: density, size, spatial distribution

•Laser heating, LIPEE: presence, size

•Photodetachment: particle charge; charging kinetics

•FTIR: particle composition

•Infrared CRD: particle formation

•Electrons and ions

Internal plasma parameters:

Page 56: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Experimental setup

• rf CCP plasma

•Homogeneous gas flow though top rf showerhead and bottom grid in closed configuration

•Controled temperature using heater/cooling system

•Variable gas: today only 5% SiH4 in Ar

Page 57: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

The “neutral chemistry” setup

Infrared CRDS

FTIR

OES

The “electrons and ions” setup

Microwave resonance

Photodetachment

PIM

Page 58: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Emission increases with time

After some time particles are ejected

Time delay depends on temperature

video

14.39

15.40

16.19

Page 59: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Plasma impedance monitor•a small capacitance and a pickup coil in rf line

Determines:

•Voltage, current en phase between them•For the fundamental frequency and the first 6 harmonics

•With a time resolution of 0.1 s

V I

RF

Page 60: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Measurement Scheme

Particle detectionDissociation processes

Electric parameters

He-Ne laser beam

OMA-

PIM

Page 61: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

0.8

0.9

1

1.1

1.2

1.3

1.4

0 20 40 60 80 100Time [s]

Fu

nd

am

en

tal cu

rre

nt

[A]

17

80

120

35

40

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0 20 40 60 80 100Time [s]

Fu

nd

am

en

tal V

olt

ag

e [

V]

17

80

120-95

-93

-91

-89

-87

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-83

-81

0 20 40 60 80 100Time [s]

Fu

nd

am

en

tal P

has

e [

de

gre

e]

17

80

120

p=0.133 mbar f=10 sccm 5%SiH4 in Ar V=155 mV (P=8 W)

current voltage phase

353K

393K

290K

3rd h

arm

onic

1st

har

mon

ic

fund

amen

tal

0

0.005

0.01

0.015

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0.025

0 20 40 60 80 100Time [s]

Fir

st

harm

on

ic [

A]

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0.0005

0.001

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0 20 40 60 80 100TIme [s]

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ird

harm

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A]

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0

0.1

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0 20 40 60 80 100Time [s]

Fir

st

harm

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ic [

V]

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0

0.05

0.1

0.15

0.2

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0 20 40 60 80 100Time [s]

Th

ird

harm

on

ic [

V]

17

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0 20 40 60 80 100Time [s]

Fir

st

harm

on

ic [

de

gre

e]

17

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-250

-200

-150

-100

-50

0

50

100

150

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250

0 20 40 60 80 100

Time [s]

Th

ird

harm

on

ic [

de

gre

e]

17

80

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Page 62: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Si-H line

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140

He-Ne laser

0

100

200

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500

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700

800

900

1000

0 10 20 30 40 50 60

Halfa line

0

20

40

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100

120

140

0 20 40 60 80

Si-H line

0

100

200

300

400

500

600

700

800

900

0 20 40 60 80

HE

-NE

Ha

SiH

170C= 290KHe-Ne laser

0

500

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3500

4000

0 20 40 60 80 100 120 140

Halfa line

0

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0 20 40 60 80 100 120 140

 

He-Ne laser

0

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0 50 100 150 200 250

Halfa line

0

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0 50 100 150 200 250

Si-H line

0

20

40

60

80

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200

0 50 100 150 200 250

800C= 353K 1200C= 393K 100 secp=0.133 mbar f=10 sccm 5%SiH4 in Ar P=8 W

Page 63: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

Same behavior in electron density measured by microwave resonance

-fast decay with several phases

-oscillations as several generations grow

-electron density growth as particles are expelled

Page 64: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

5 mm

Page 65: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

10 mm

500 nm

Page 66: Master Class: Electronegative Plasmas September 28-30

Master Class: Electronegative Plasmas September 28-30

The End