CST korean user meeting-KAIST-plasma

2009 CST Korean user meeting1

Development of VHF Inductively Coupled Plasma (ICP) Source using a CST Microwave Studio

KAIST, Low-temperature plasma lab. Samsung electronics, Etch process team

Hyun-su Jun

Electronic mail: [email protected]

Development of VHF Inductively Coupled Plasma (ICP) Source using a CST Microwave Studio

KAIST, Low-temperature plasma lab. Samsung electronics, Etch process team

Hyun-su Jun

Electronic mail: [email protected]


CONTENTSCONTENTS

1. Introduction

1.1. Inductively coupled plasma 1.2. Necessity for low-electron-temperature plasma1.3. Problems in VHF-ICP operation1.4. Antenna voltage and plasma uniformity

2. VHF-ICP source development

2.1. Antenna theory of VHF-ICP source2.2. Capacitor Distributed Resonance Antenna (C.D.R.A.)2.3. Plasma model setup in CST-MWS2.4. Impedance matching in CST-MWS2.5. Analysis of field simulation results

3. Experimental results

3.1. Structure of Capacitor Distributed Resonance Antenna3.2. Plasma parameter measurements

4. Summary


1. Introduction1. Introduction

Inductively coupled plasma (ICP)Inductively coupled plasma (ICP)

Gas inlet

Gate Valve

Ground Turbo Pump

RotaryPump

Single Langmuir Probe

Plasma, ne~1011/cm3

I.M.B.

13.56 MHz RF

Antenna GND

Plasma medium

Powered end

Groundedend

tHE∂∂

−=×∇ 0µ

Faraday’s law

θE

LVrf ω~

Sheath layercmnTlengthDebyes eem )/740(5)(5~ =

Dielectric window

Antenna

)(

2

c

pr iνωω

ωεε

−−= ∞

Applications: spacer etch, trench etch, contact etch… Debye length



Necessity for lowNecessity for low--electronelectron--temperature plasmatemperature plasma

High electron temperature

Low etch selectivityProfile angle problem

Radical density ratio [CFx/F] as a function of electron temperature

H. Kokura, 2000 Jpn. J. Appl. Phys.

311103 −×= cmne

MaxwellianeVTb 75.2=

MaxwellianbieVTtempTail t

−= 5.3.

MaxwellianbieVTtempTail t

−= 0.5.

Trench etch (0.2 mm wide by 4 mm deep)in single-crystal silicon

Ion trajectory bending

Electron



Necessity of lowNecessity of low--electronelectron--temperature plasmatemperature plasma

Measured EEPFsD. S. Lee, H. S. Jun Thin Solid Films, 2006

Measured EEPFsH. S. Jun Applied Physics Letters, 2007

→ The Electron temperature (Teff) decreased with an increase in the driving frequency.



Problems in VHFProblems in VHF--ICP operationICP operation

E-field distribution at 13.56MHz

Antenna current -vector at 13.56 MHz

E-field distribution at 60 MHz

Antenna current -vector at 60 MHz

→ Because of the node-effect in the VHF-ICP source, an inductive discharge(H-mode) is practically impossible over the frequency of 60 MHz.



Antenna voltage and plasma uniformityAntenna voltage and plasma uniformity

Antenna’s powered end

Sputtering map on dielectric window Azimuthal electric field distribution

Antenna’s powered end

→ Antenna voltage distribution is the key factor in uniform plasma generation.


2. VHF-ICP source development2. VHF-ICP source development

Antenna theory of VHFAntenna theory of VHF--ICP sourceICP source

TL LIV ω=

2T

RLIV ω=

4T

RLIV ω=

TL

TC2 TC2

TC4 TC4 TC4 TC4

2/TL 2/TL

4/TL 4/TL 4/TL 4/TL

V

LI

RI

RI

GND

GND

GND

0

0=N

2=N

4=N

22 1

⎟⎟⎠

⎞⎜⎜⎝

⎛Ω+−+==

TTLT C

LRIIZVω

ω

TL LX ω= TC CX ω/1=

RCL atXX ωω == 22 Ω+== RIZIV RLRT

Ti NCC = Tic NCX ω1= TRicRic NCIXIV ω==

NLL Ti /= NLX TiL /ω= NLIXIV TRiLRiL /ω==

Total antenna impedance

L-C series resonance condition

Local antenna voltage drop

→ The local voltage drop of each antenna segment is inversely proportional to the number of segments N.


Capacitor Distributed Resonance Antenna (C.D.R.A.) Capacitor Distributed Resonance Antenna (C.D.R.A.)

Main purpose of CST-MWS simulation Verification of the azimuthal E&H field distribution at the antenna resonance freq. Analysis of the impedance match condition

Low antenna voltage & high antenna current

Antenna L-C series resonance

High density & low electron temperature plasma

capacitors

Power input Antenna ground



Plasma model setup in CSTPlasma model setup in CST--MWSMWS

)(

2

c

pr iνωω

ωεε

−−= ∞

e

ep m

ne

0

2

εω =

1=∞ε

)( egc TKn=ν


Ref. Michael A. Lieberman “Principles of plasma discharges and materials processing”.

Plasma dielectric constant

Electron plasma frequency


Impedance matching in CSTImpedance matching in CST--MWSMWS


Direct calculation: MWS stand-alone type

Indirect calculation: MWS-DS co-simulation type

0 20 40 60 80

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

S11

para

met

er

Driving frequency (MHz)

13.56 MHzImpedance matching point

Load impedance calculation from MWS simulation

Matching condition analysis

Load impedance

Lumped elements


Analysis of field simulation results Analysis of field simulation results

0 60 120 180 240 300 360

0

1000

2000

3000

4000

5000

Azimuthal angle [degree]

Azi

mut

hal E

elec

tric

fiel

d [V

/m]

Single turn 13.56 MHz Single turn 27.12 MHz Single turn 40.68 MHz C.D.R.A. 61.40 MHz

0 60 120 180 240 300 3601.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Single turn 13.56 MHz Single turn 27.12 MHz Single turn 40.68 MHz C.D.R.A. 61.40 MHz

Azimuthal angle [degree]

Azi

mut

hal M

agne

tic fi

eld

[A/m

]M

agne

tic fi

eld

ampl

itude

Ele

ctri

c fie

ld a

mpl

itude


According to the field simulation results, the C.D.R.A. gives a uniform distribution in the electric and magnetic fields.

Evaluate field onpredefined curve


Structure of Capacitor Distributed Resonance AntennaStructure of Capacitor Distributed Resonance AntennaC

.D.R

.A.

base

-PC

B

Plas

ma

disc

harg

e a

t 40

MH

z

Con

vect

ion

cool

ing

syst

em

Cooling fan

Diameter = 450 mm

Capacitor

Cap

acito

r co

nnec

tion

Power portAntenna ground

Capacitance uncertainty is

100 pF ± 1 pF for 12 capacitors

Top plateBase plate

Ref. H. S. Jun, H. Y. Chang, Appl. Phys. Lett. 92, 041501 (2008).

3. Experimental results 3. Experimental results


Plasma parameter measurements Plasma parameter measurements

3. Experimental results 3. Experimental results

0 5 10 15 20 25 300.0

2.0x1011

4.0x1011

6.0x1011

8.0x1011

1.0x1012

1.2x1012

1.4x1012

1.6x1012

δ=-9.21E8

δ=-4.35E9

δ=-7.12E9

Ele

ctro

n de

nsity

(cm

-3)

Position (cm)

rf power 1.6 KW 5 mTorr 10 mTorr 30 mTorr

0 5 10 15 20 25 300.0

2.0x1011

4.0x1011

6.0x1011

8.0x1011

1.0x1012

1.2x1012

1.4x1012

1.6x1012

δ=1.19E8

δ=6.02E8

δ=2.32E9

Ele

ctro

n de

nsity

(cm

-3)

Position (cm)

rf power 1.6 KW 5 mTorr 10 mTorr 30 mTorr

0 5 10 15 20 25 300

1x1011

2x1011

3x1011

4x1011

5x1011

6x1011

7x1011

8x101110 mTorr Ar plasma

Position (cm)

Ele

ctro

n de

nsity

(cm

-3)

0.8 KW δ=-2.12E9 1.0 KW δ=-2.93E9 1.2 KW δ=-3.66E9 1.4 KW δ=-4.13E9 1.6 KW δ=-5.14E9

0 5 10 15 20 25 300

1x1011

2x1011

3x1011

4x1011

5x1011

6x1011

7x1011

8x1011

Ele

ctro

n de

nsity

(cm

-3)

Position (cm)

10 mTorr Ar plasma 0.8 KW δ=4.29E8 1.0 KW δ=4.75E8 1.2 KW δ=3.88E8 1.4 KW δ=5.91E8 1.6 KW δ=6.02E8

The worst radial plasma uniformity exists at the powered

end of the antenna.

Power input

Probe scanning direction

Single turn antenna

Single turn antenna

C.D.R.A.

C.D.R.A.

Symmetric plasma density


““CSTCST--MWSMWS”” based plasma source developmentbased plasma source development

Plasma uniformity prediction through the E/H-field and power loss distribution.

Plasma source S-parameter analysis.

Impedance-matching-network design for different antenna types.

High-frequency & large-area plasma source analysis.

SummarySummary

See also…Wave-cutoff probe

H. S. Jun, B. K. Na, H. Y. Chang, and J. H. Kim, Phys. Plasmas 14, 093506 (2007).

Wave-cutoff probe simulation

Documents

CST korean user meeting-KAIST-plasma