Northeastern University Boston, 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 teflon Dielectric constant εr=10.8 Dielectric thickness: 635µm

Conductor: Copper Conductor thickness: 9 µm

Operation Conditions

900 MHz 0.1 - 760 torr 0.150 - 3 W

Ground Plane Dielectric

Discharge gap

Lin e

SMA connector

Discharge Gap

λ/4

~ 2 cm

~ 5

cm

λ/2

Matching network

Split ring resonator

I V

? 2

Principle of Operation

Discharge gap

g o h

E 2 E g

≈ Ground Plane

Dielectric

g

h Eo

Eg

Line

Ground plane

Line plane

Section AA’

Ground plane

Line plane

Section BB’

A’

A B’

B Magnitude of the electric field |E| Simulation using HFSS from Ansoft

Experiment Set-up

Glass tube

(chamber)

Manifold

Plasma SourceGas outlet

To pressure gauges

Coaxial Probe

Gas inlet

Needle valve

30dB

900.000 -7.3

MKS

0.53

0.53 - - -

Ignition Power & Gap engineering

Pressure (torr)

Ig ni

tio n

Po w

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

0.8 0.9

2

4

5

Pressure Range of Operation

Probe diagnostics: v Ion Density ~1011cm-3

v Floating Potential

Probe diagnostics: Ion density

100 mtorr 200 mtorr 300 mtorr 400 mtorr

Power (W) 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Io n

D en

si ty

n ii (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 resonator 400 mtorr

335Q ≈

40Q ≈

Argon

Probe diagnostics: Floating Potential

Pressure (torr)

0.01 0.1 1 10 100 1000 10000

Fl oa

tin g

Po te

nt ia

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

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

*l am

bd a/

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 W 1st Positive Band: 3 3 +g uB ? A→ ∑2nd Positive Band:

3 3 u gC ? B ?→

∆ν = ... 0 2 3 41 -3 -1-2- 4

∆ν = ...

N2 Ground state

ν=1

N2+

ν=2 ν=3

ν=1 ν=2 ν=3

3 + uA ∑

3 gB Π

3 uC Π

... ...

...

ν=1 ν=2 ν=3

N2+

Tvib = 0.70 eV (8124 K)

Tvib = 0.25 eV (2901 K)

N2:1 st positive band

N2:2 nd positive band

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

Wavelength (Å)

In te

ns ity

(a .u

.)

Ar* Ar+

Argon

Texc = 0.32 eV (3714 K)

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

* *

* ** **

* *

***** **

Boltzmann plot

4000 5000 6000 7000 8000 90000 0.2 0.4 0.6 0.8

1

Wavelength (Å)

In te

ns ity

-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=2 ν=3

ν=1 ν=2 ν=3

3 + uA ∑

3 gB Π

3 uC Π

... ...

...

ν=1 ν=2 ν=3

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

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

2- 4

1- 3

0- 2

Trot = 350 K

Trot = 400 K

Trot = 450 K

gas rotT T = 400 K≈

Conclusions NEW DEVICE BASED ON A SPLIT-RING RESONATOR v Low cost, robust and high-Q v Low-Power

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

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

SPECTRUM ANALISYS v Non-thermal plasma v 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