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Study of Electronegativity in Inductively Coupled Radio-Frequency
Plasma with Langmuir Probe
Dept. Energy Sciences
Tokyo Institute of Technology
Hotta Lab
D1 Bin Huang (黄 斌)
International Training ProgramQueen’s University Belfast
About Queen’sDirector: Prof. Bill Graham
Cooperator: Mr. Mujahid
Main building of Queen’s
Inductively Coupled Plasma (ICP)
Introduction to ICP
Type: planar/cylindrical
Principle:
time-varying current through coil
time-varying magnetic field
induces azimuthal electric currents
break down forming plasma
Oxygen ICP applicationSemiconductor manufacture
photo resist is applied to the wafer
photo mask hardens/illuminates resist
Deposition/etching
Cleaning wafer
Oxygen +polymers /organics CO2+H2OAshing:
Oxygen ICP characteristics
Two operation regimes:
E-mode: low power, low density,
capacitive discharge.
H-mode: high power, high density,
inductively discharge.
E-H transition:
change of electron density, EEDF,
coil current, light emission, etc.Negative ions:O-,O2
-, O3- ,etc
Photo-detachment measuring system
Nd:Yag laser 532nm
Langmuir Probe
Schematic of photo-detachment measurement system
GEC reference cell
Electrode diameter: 165.1 mmElectrode gap: 40.5 mm
Upper electrode
Lower electrode
RF:13.56 MHz
Photo-detachment diagnostics
Diagnostics principle:
Less perturbing Better time resolution Capacity of measuring ion temperature
A-+hν=A+e
electron affinities:O-:1.46 eV; O2
-:0.44 eVNd:YAG laser(532 nm): hν=2.33 eV
Suffice to photo-detach both species
Advantages:
Photo-detachmentelectron current
E:incident laser power
S:beam cross-sectional area
σpd: photo-detachment cross section
of negative ion
Photodetachment fraction Vs laser energy
Photo-detachment fraction:
0 5 10 15 20 25 30 35 40 45 50
0.0
0.5
1.0
1.5
2.0
Ph
oto
de
tac
he
mn
t fr
ac
tio
n 400W 100mtorr
20mtorr 50W
theory
Energy (mJ)
Photo-detachment fraction against energymeasured with probe 1.25 cm from lowerelectrode with laser diameter of 5 mm.
Deviate from theory:thermionic electron emissionlaser ablation of the probe surface
Negative ion density:
Ie: probe current
ne: background density
ΔIe: instantaneous current
Theoretical:
Experimental:
0 10 20 30 40 50 60
0
10
20
30
40
50
60
Ele
ctr
on
eg
ati
vit
y
Negative ion current
Electron Current
A.
U.
Probe bias (V)
0.0
0.5
1.0
1.5
2.0
2.5
Electronegativity
0 10 20 30 40 50
0.0
0.1
0.2
0.3
0.4
0.5 Electronegativity
Negative ion current
Electron current
A.U
.Bias Voltage (V)
400W 100mtorr
Electronegativity (blue), Negative ion current(black) and electron current (red) against probebias voltage in capacitive mode.
Electronegativity (black), Negative ion current(red) and electron current (green) against probebias voltage in inductive mode.
Probe bias voltage Probe bias voltage
Electronegativity Vs probe bias
Capacitive mode:Electronegativity stablize @45 V
Inductive mode:Electronegativity stablize @30 V
elec
tro
neg
avit
y
0.0 0.5 1.0 1.5 2.0 2.5 3.0
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
2mm
3mm
4mm
5mm
~6mmAm
pli
tud
e (
mV
)
Time (s)
2 3 4 5 6
0.2
0.4
0.6
0.8
1.0 30mtorr 50W
A U
Diameter (mm)
Electronegativity Vs laser diameterr
Electronegaticity stablizes @ 5 mm
elec
troneg
avit
y
Electronegativity against pressure
5 10 15 20 25 30 35 40
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
50W
100W
150W
Ele
ctr
on
eg
ati
vit
y
Pressure (mtorr)
0 5 10 15 20 25 30 35 40
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
50W
100W
150W
Ele
ctr
on
eg
ati
vit
y
Pressure (mtorr)
2cm from the ground 1.25cm from the ground
O-is produced by dissociative attachment of O2 and destroyed by ion-ionrecombination at low pressures. At higher pressures it is lost due todetachment.
Capacitive mode
Peak electronegativity when RF power fixed:
Electronegativity decreased when RF power increase:Electron density increases while negativity ion density is almost constant
10
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
50W
100W
150W
Ele
ctr
on
eg
ativity
Pressure (mtorr)
Electronegativity against pressureCompared with simulation
From Corrmac. Corr Ph.Dthesis
Conclusion & future work
Laser energy, laser diameter and probe bias voltage were calibrated
and suitable parameters were selected for photo-detachment
measurement.
Electrongativity were measured at different positions in capacitive
mode.
The relationship between electronegaticity and pressure & RF power
is consistent with simulation.
Measuring electronegativity against pressure in inductively mode
< Future work: >
< Conclusion: >
Electronegativity against pressure
Inductive mode1.25 cm from lower electrode
0 20 40 60 80 100
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
400W
300W
Ele
ctr
on
eg
ativity
Pressure (mtorr)
The relationship isnot clear and shoulddo again.
0 10 20 30 40 50 60 70 80 90 100
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
2nd measurment 300W
1st measurment 300W
Ele
ctr
on
eg
ati
vit
y
Pressure (mtorr)
Electronegativity against pressureCompared with simulation
5 10 15 20 25 30 35 40
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
50W
100W
150W
Ele
ctr
on
eg
ati
vit
y
Pressure (mtorr)
Global model
From Corrmac. Corr thesis
Self introduction
Name: Bin Huang (黄 斌)
Hometown : Suzhou, China (蘇州,中国)
Research in Tokyo Tech: Xe gas jet type Z-pinch EUV source
Research in Queen’s: Oxygen radio-frequency ICP
Oxygen Inductively Coupled Plasma
◊surface modification◊fabrication of chips◊thin film deposition
Two operation regimes:
E-mode: low power, low density,
capacitive discharge.
H-mode: high power, high density,
inductively discharge.
E-H transition:
change of electron density, EEDF,
coil current, light emission, etc.
Negative ions:O-,O2
-, O3- ,etc
< Application: >
O2- is less than 10%