Northeastern UniversityBoston, MA

- USA -

LLOWOW--PPOWEROWER µµWAVEWAVE PPLASMALASMA

SSOURCEOURCE FFOROR MMICROSYSTEMSICROSYSTEMS

Felipe Iza and Jeffrey A. HopwoodFelipe Iza and Jeffrey A. Hopwood

ICOPS - Cheju, 2003

Outline

DEVICE DESCRIPTION

v Low-cost gap-excited microwave plasma source

v Low-power device

v Atmospheric pressure

PROBE DIAGNOSTICS

v High-density discharge

v Low sheath voltage

SPECTRUM ANALISYS

v Non-equilibrium, low-temperature discharge

CONCLUSIONS

Plasma Source Description

RT/Duroid 6010.8

Dielectric: Ceramic reinforced teflonDielectric constant εr=10.8Dielectric thickness: 635µm

Conductor: CopperConductor thickness: 9 µm

Operation Conditions

900 MHz0.1 - 760 torr0.150 - 3 W

Ground PlaneDielectric

Discharge gap

Line

SMA connector

Discharge Gap

λ/4

~ 2 cm

~ 5

cm

λ/2

Matching network

Split ringresonator

I V

?2

Principle of Operation

Discharge gap

g oh

E 2 Eg

≈Ground Plane

Dielectric

g

hEo

Eg

Line

Groundplane

Lineplane

Section AA’

Groundplane

Lineplane

Section BB’

A’

AB’

BMagnitude of the electric field |E|Simulation using HFSS from Ansoft

Experiment Set-up

Glass tube

(chamber)

Manifold

PlasmaSourceGas outlet

To pressure gauges

Coaxial Probe

Gas inlet

Needlevalve

30dB

900.000 -7.3

MKS

0.53

0.53- - -

Ignition Power & Gap engineering

Pressure (torr)

Igni

tion

Pow

er (W

)

0.1 1 10 100

1

6

760

3

0.5

500 µm gap - Argon

50 µm gap - Argon

500 µm gap - Air

0.6

0.7

0.80.9

2

4

5

Pressure Range of Operation

Probe diagnostics:v Ion Density ~1011cm-3

v Floating Potential <5V

Spectroscopy:v Trot = 400K v Tvib = 0.7eVv Texc = 0.32eV

Ar plasma @ 1W, 900 MHz

Glass tube

Microstrip

Glass tube

Microstrip

Glass tube

0.1 torr 10 torr 760 torr100 torr

Probe diagnostics: Ion density

100 mtorr 200 mtorr300 mtorr400 mtorr

Power (W)0.0 0.2 0.4 0.6 0.8 1.0 1.2

Ion

Den

sity

nii(c

m-3

)

0.0

2.0e+10

4.0e+10

6.0e+10

8.0e+10

1.0e+11

1.2e+11

1.4e+11

[1] Iza F. and Hopwood J., Plasma Sources Science and Technology, vol. 11, no. 3, pp. 229-235, August 2002

mICP @ 400 mtorr[1]

mICP 400 mtorr[1]

Ring resonator400 mtorr

335Q ≈

40Q ≈

Argon

Probe diagnostics: Floating Potential

Pressure (torr)

0.01 0.1 1 10 100 1000 10000

Floa

ting

Pote

ntia

l (V

)

-5

0

5

10

15

20

25

1250 mW

1000 mW

750 mW

250 mW

500 mW

150 mW

Probe: Thin gold wire (d=50µm)

Argon

Pressure Range of Operation

Probe diagnostics:v Ion Density ~1011cm-3

v Floating Potential <5V

Spectroscopy:v Trot = 400K v Tvib = 0.7eVv Texc = 0.32eV

Ar plasma @ 1W, 900 MHz

Glass tube

Microstrip

Glass tube

Microstrip

Glass tube

0.1 torr 10 torr 760 torr100 torr

Ar: 760 torr, 1.5 W

4000 5000 6000 7000 8000 9000 10000

4000 4500

Texcitation and Tvibrational @760 torr

Ar Ground state

E (eV)Ar+

Ar*

15

10

5

13

-14

-12

-10

-8

-6

-4

-2

0

2

ln(I

*lam

bda/

A)

7 8 9 10 11 12 14 15-16

Energy (eV)16

4000 5000 6000 7000 8000 9000

99.9% Ar + 0.1% N2 : 760 torr, 1.5 W1st Positive Band: 3 3 +

g uB ? A→ ∑2nd Positive Band: 3 3u gC ? B ?→

∆ν = ...0 2 3 41 -3 -1-2- 4

∆ν = ...

N2 Ground state

ν=1

N2+

ν=2ν=3

ν=1ν=2ν=3

3 +uA ∑

3gB Π

3uC Π

......

...

ν=1ν=2ν=3

N2+

Tvib = 0.70 eV(8124 K)

Tvib = 0.25 eV(2901 K)

N2:1st positive band

N2:2nd positive band

00.10.20.30.40.50.60.70.80.9

1

Wavelength (Å)

Inte

nsity

(a.u

.)

Ar* Ar+

Argon

Texc = 0.32 eV(3714 K)

********** ****

**

*****

**

*******

Boltzmann plot

4000 5000 6000 7000 8000 900000.20.40.60.8

1

Wavelength (Å)

Inte

nsity

-3 -1-2- 4

1st Positive Band: 3 3 +

g uB ? A→ ∑2nd Positive Band: 3 3

u gC ? B ?→

∆ν = ...0 2 3 41∆ν = ...

Rotational Temperature Trot @760 torr

N2 Ground state

ν=1

N2+

ν=2ν=3

ν=1ν=2ν=3

3 +uA ∑

3gB Π

3uC Π

......

...

ν=1ν=2ν=3

99.9% Ar + 0.1% N2 : P=760 torr, 1.5 W

3680 3700 3720 3740 3760 3780 3800 3820Wavelength (Å)

2-4

1-3

0-2

Trot = 350 K

Trot = 400 K

Trot = 450 K

gas rotT T = 400 K≈

ConclusionsNEW DEVICE BASED ON A SPLIT-RING RESONATOR

v Low cost, robust and high-Qv Low-Power

Ø 0.5W Argon @ 760torrv Wide pressure range operation Ø 0.1-760 torr

PROBE DIAGNOSTICS (LOW PRESSURE)v High-density dischargev Small sheath voltage at pressures > 3 torr

SPECTRUM ANALISYS

v Non-thermal plasmav 99.9% Ar +0.1%N2, 760 torr, 1.5W ØTexc= 0.32eV (3714 K)ØTvib= 0.7eV (8124 K)ØTrot= 0.03eV (400K)

PORTABLE DEVICE

EFFICIENT AND DURABLE

LOW-TEMP.APPLICATIONS

This research has been supported by Northeastern University, the Fulbright Program, and the National Science Foundation under Grant No. DMI-0078406.

Acknowledgment