Design of compact Microwave Plasma Ion Sourcesnuplex.snu.ac.kr/new/archives/upload/pt_pdf58.pdf · 2012. 4. 2. · NUPLEX, Dept. of Nuclear Eng., Seoul National University San 56-1,

(+) Bias Electrode

PlasmaBubble

Ambient Plasma

Design of

Ambient Plasma

Design of compact Microwave Plasma Ion Sources

for Focused Ion Beamfor Focused Ion Beam

대한기계학회 - 2008 생산 및 설계공학부문 춘계학술대회

June 4th, 2008, Jeju Oriental Hotel, Jeju, Korea

Yeong-Shin Park*, H.T. Kim, and Y.S. Hwang

NUPLEX, Dept. of Nuclear Eng., Seoul National University

San 56-1, Shillim-dong, Gwanak-gu, Seoul 151-742, Korea

* [email protected]

Design of compact Microwave Plasma Ion Source for FIB

1/15Contents

1. Introduction - Focused Ion Beam and Ion Source

2. Plasma and Plasma Ion Source

3. RF Plasma Ion Source and Local Sheath Plasma

4 Microwave Plasma Ion Source4. Microwave Plasma Ion Source

5. Two Types of MWPIS for FIB

6. Open Cavity Resonator type MWPIS1. Rectangular cavity and antenna design

2. Optimum cavity length

7 Insulated Antenna type MWPIS7. Insulated Antenna type MWPIS1. Cavity and insulated antenna design

2. Beam extraction result

8. Summary & Conclusion

NuplexNuplexNuplex대한기계학회 - 2008 생산 및 설계공학부문 춘계학술대회



2/15Focused Ion Beam and Ion Source

Low Emittance Small Virtual Low Emittance Small Virtual ◈ FIB system and its applications[1]

▶ FIB : Ion Source + Lens ▶ Requirement of ion source

( High Brightness ) Source Diameter dv

High Current, Low Energy Spread

( High Brightness ) Source Diameter dv

High Current, Low Energy Spread

▶ High Brightness Ion Sources : LMIS, PIS◈ Liquid Metal Ion Source(LMIS) ◈ Plasma Ion Source(PIS)

h b h

Limited species : Ga, In

Ga+ ion bombardment

Undesired alloy formation▶ Image-side Beam spot size

High emittance

Low Current High Current

Low emittance

High brightness

Undesired alloy formation

Short operation time

Hard to make multi-beam

Wide ion energy distribution

2 2 2 2 1/2( )cv sdd M d d= + +

▶ Image-side Beam spot size High Current

High brightness plasma ion source



[1] S. Reyntjens and R. Puers, “A review of focused ion beam applications in microsystem technology”, J. Micromech. Microeng. 11, 287 (2001)


3/15Plasma and Plasma Ion Source

+

negative bias+

e+

+

e

+

e

e

Eiz[eV]

Ion BeamN

+

e

N

e

N

+

e

N

+N

e Nee

+

e

+

N

e

positive biaseN

+

e

N+

eN ++

e

+

e

+

e Ne

N

Ne

e

Electron Beam

NeNeNe

Plasma

e Ne

Electric Field

Plasma

† Forth State of Material solid, liquid, gas, plasma

Plasma generation

† collisions between particleshaving energy over ionization

Particle Beam Source

† unlimited ion speciesAr, He, Ne, H, D, O, ……q g p

† electrons, ions, neutrals

† quasi-neutral stateni = ne → plasma density

potential

† the energy generally from electric field generated by DC, AC, RF, Microwave powers.

, , , , , ,

† multi-beam extraction

† long lifetime

† pressure, power




4/15RF Plasma Ion Source and Local Sheath Plasma

◈ ICP RF Plasma Ion Source[2]

107

108

LMIS 10μA1 eV-1]

ICP ◈ Comparison of brightness between RF PIS and LMIS[2]

LSP

( ) Bi

105

106 SNU 1.4μA SNU 3.1μA

ess [

A m

-2sr

-

◈ Local Sheath Plasma(LSP)[2]

PlasmaBubble

(+) Bias Electrode

102

103

104

m. B

righ

tne

Typical range of beam current Ambient Plasma

10-4 10-3 10-2 10-1 100 101 102 103101

0N

orm

Beam Current [nA]

used in FIB system



[2] Yoon Jae Kim, Yong Shin Park, Dong Hee Park, and Yong Seok Hwang, “High Brightness Plasma Ion Source for Nano Fabrication”, presented at 2007 International Conference on Ion Sources, Aug. 27-31, 2007, Danguk Univ., Korea


5/15Microwave Plasma Ion Source

† It is possible to heat without collision. L d d i

▶ Wave heating * General Properties of High Density Plasma (including ECR)

: Landau damping

† Low pressure operation

† Continuous acceleration of electrons

Pressure (mTorr)

Power (W)

Frequency (MHz)

Magnetic Field (kG)

0.5 - 50

100 - 5000

0 - 2450

0 - 1

Plasma Density (cm-3)

Electron Temperature (eV)

1010 – 1012

2 - 7▶ Generally used microwave power

† Wavelength : 12.24 cm

† Frequency : 2 45 GHz ▶ Electron cyclotron resonance(ECR)† Frequency : 2.45 GHz

▶ Compactness

† small matching system ECR multiply charged ions

▶ Electron cyclotron resonance(ECR) and off-resonance Plasma

▶ Noise free

† f f l t i l i t f

: using small stub not large matching box as RF plasma

- multiply charged ions - operation in an extremely wide range of gas pressures or particles - high degree of ionization and plasma density

▶ Long lifetime

† free from electrical interference

† non-plasma-contacted electrode

Off resonance- singly charged ions



† p


6/15Two Types of MWPIS for FIB

▶ Open Cavity Resonator type† Rectangular cavity

▶ Insulated Antenna type† Insulated antenna

† Resonant electric field

† Easy to breakdown

† High electric field / compact

† ECR or off-resonance

▶ Requirement of ion sources for FIB

† Compact† Noise free

† High current† Low emittance

† Low energy spread

† Various ion species† Long life time

† High voltage break

Cavity ResonatorMWPIS

Insulated AntennaMWPIS

RF Plasma Ion Source

MWPIS




7/15Open Cavity Resonator type MWPIS

◈ Overview of insulated antenna type MWPIS




8/15Design of Rectangular Cavity Resonator

◈ Rectangular cavity[3]

2 2 2⎛ ⎞ ⎛ ⎞ ⎛ ⎞

Resonance frequency of the TEmnl mode

db

2 2 2

2,

mnlr r

r r

c m n lfa b d

permittivity permeability

π π ππ μ ε

ε μ

⎛ ⎞ ⎛ ⎞ ⎛ ⎞= + +⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠

= =a

† a = 100 mm, b = 25 mm, d = 155 mm

r r

▶ TE102 mode for 2.45 GHz

60mm

◈ Rectangular cavity and quartz tube drawn at HFSS[3] ◈ Electric field calculated from HFSS[3]

100mm

155mm25mm



[2] 김현태, 박용신, 성충기, 이재령, 황용석, “Design and Characterization of a Microwave Plasma Source using a Rectangular Resonant Cavity”, presented at 34th confereneceof Korean Vacuum Society, Feb. 13-14, 2008, Danguk Univ., Korea


9/15Fabrication of Rectangular Cavity Resonator MWPIS

† Rectangular cavity : Copper

† Movable cavity door : from 135 mm to 160 mm

◈ Rectangular cavity resonator MWPIS[3]

† Antenna : located at ¼ ‘d’, N-type connector, attaching disk at the end of antenna

† Discharge tube : Quartz, located at ¾ ‘d’

◈ Rectangular cavity resonator with movable door[3]

about 60 mm in diameter

d

Movable cavity door




10/15Optimum Cavity Length for Breakdown

◈ Breakdown power as varying Ar gas pressure and cavity length[3]

500

600

]

160mm 155mm 150mm145mm

† Optimum Pressure : around 0.6 Torr

† Lower Pressure Region: neutral particles contribute to discharge

300

400

wn

pow

er[W

] 145mm 140mm 135mm

p g

† Higher Pressure Region: pretty much collisions interfere for electron to gain energy

200

300

brea

kdow † Optimum Cavity Length

: 140 ~ 145 mm: shorter than calculated result (155 mm): quartz and boundary conditions

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

100: quartz and boundary conditions: effective permittivity (Ar, air and quartz) is higher than ideal permittivity(vacuum).

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

pressure[Torr]




11/15Insulated Antenna type MWPIS

◈ Overview of insulated antenna type MWPIS




12/15Design of Magnetic Field

† 6 permanent magnets – ring shape, I.D. : 50 mm, O.D. : 80 mm, Height : 10 mm

† NdFe35 : Large magnetism, cheap (SmCo24,28 : good magnetism/thermal resistance, expensive)

† Maximum magnetic field : 1.8 kGauss

† Electron cyclotron resonance : 875 Gauss at 2.45 GHz, ◈ Axial magnetic field at the center of magnet and position

of electron cyclotron resonance positionantenna position at high B-field regionboth ECR and off-resonance microwave plasma

◈ Six ring magnets(left) and magnetic-field strength(right)

of electron cyclotron resonance position

calculated in Maxwell 3D ECR region 875 Gauss




13/15Design of Cylindrical Cavity and Antenna

† Cylindrical Cavity – stainless steel, I.D.: 46 mm, height : 50 mm

† Powered Antenna – copper, O.D. 10 mm, terminated disk, N-type connector ,optimum position : 28 mm away from bottom (HFSS simulation)

† Effective electric field : ~2x104~2x103 V/m (input voltage 100 V) (HFSS simulation)

† Dielectric discharge chamber : Pyrex glass, screening antenna from plasma

◈ Cylindrical cavity and antenna drawn at HFSS ◈ Electric field distribution ◈ Dielectric chamber and Antenna adopting N-type connector




14/15Ion Beam Extraction

100

◈ Beam and bias current as varying bias voltage without B-field(Ar, 1sccm, MW power : 150W, Aperture : 1 mm)

◈ S

▶ Bias Current

▶ Ion Beam Current

100 Beam Current Bias Current

Breakdown of Local S

80

100

80 1.0sccm 1.0sccm 1.0sccm 2.5sccm3 0

◈ Saturated bias current w.r.t. power and flow rate

10

urre

nt [μA

]

Sheath Plasma

40

60

Bias C

urren

40

60

atur

atio

n C

urre

nt [m

A]

3.0sccm

1

Mi Pl

Bea

m C

20

nt [mA]

100 150 2000

20Sa

Microwave Power [W]

0 10 20 30 40 50 60 70 80 90 1000.1

Microwave Plasma +

Bias Voltage [V]

Microwave Plasma only Local Sheath Plasma0

† To increase bias current

Higher microwave power

† Using bias method : Local Sheath Plasma occurs at 60 V

† Over 200 μA (~25 mA/cm2) Ar+ Ion beam

† Beam current is proportional to bias current

Lower pressure



† Beam current is proportional to bias current


15/15Summary & Conclusion

Plasma ion source is regarded as a promising key to improve FIB.

Bright of RF plasma ion source have almost reached to that of LMIS.

Microwave plasma ion source has benefits to be adopted to FIB.

Open rectangular cavity resonator type MWPIS has been designed.Considering resonance frequency, geometry of resonator for TE102 has been achieved.Position of antenna and discharge chamber has been determined from simulation result.Optimum cavity length for efficient breakdown has been investigated.Optimum cavity length for efficient breakdown has been investigated.

MWPIS adopting insulated antenna has been newly introduced.Powered antenna is immersed in plasma in order to maximize electric field.However, the antenna is insulated from plasma by dielectric chamber.p yBoth off-resonance and ECR plasma can be generated by using ring shape magnets.

25 mA/cm2 Ar+ ion beam has bean achieved.Beam current density would be increased by optimizing extraction condition and decreasing operating pressure.



(+) Bias Electrode

PlasmaBubble

Ambient PlasmaAmbient Plasma

Thanks for your Attention!

bl @ k

Thanks for your Attention!

Please contact to [email protected]

Documents

Design of compact Microwave Plasma Ion Sourcesnuplex.snu.ac.kr/new/archives/upload/pt_pdf58.pdf · 2012. 4. 2. · NUPLEX, Dept. of Nuclear Eng., Seoul National University San 56-1,