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%